WORLD METEOROLOGICAL ORGANIZATION
GLOBAL ATMOSPHERE WATCH
No. 140
WMO/CEOS REPORT on a STRATEGY for
INTEGRATING SATELLITE and
GROUND-BASED OBSERVATIONS of
OZONE
JANUARY 2001
WORLD METEOROLOGICAL ORGANIZATION
GLOBAL ATMOSPHERE WATCH
No. 140
WMO/CEOS REPORT on a STRATEGY for
INTEGRATING SATELLITE and
GROUND-BASED OBSERVATIONS of
OZONE
WMO TD No. 1046
List of Contents
Foreword ...................................................................................................................................... iii
Executive Summary...................................................................................................................... v
Milestones in the History of Ozone ............................................................................................ ix
1.
Introduction.......................................................................................................................... 1
1.1 The IGOS Strategy ................................................................................................. 1
1.2 The Ozone Project.................................................................................................. 2
1.3 Requirements and Data Sources .......................................................................... 5
1.4 The Objectives of the Report ................................................................................ 9
2.
User Requirements............................................................................................................ 11
2.1 Sources of Information and Definitions ............................................................. 11
2.2 Relationships between Applications and Requirements .................................. 13
2.3 The Requirements................................................................................................ 14
3.
Available and Planned Measurements ............................................................................. 21
3.1 Introduction .......................................................................................................... 21
3.2 Non-Satellite Measurements ............................................................................... 21
3.3 Satellite Measurements ....................................................................................... 35
4.
Harmonisation of Provisions and Requirements ............................................................ 47
4.1 Introduction .......................................................................................................... 47
4.2 Total Column Ozone ............................................................................................ 47
4.3 Ozone Vertical Profile .......................................................................................... 49
4.4 Meteorological Parameters ................................................................................. 51
4.5 Related Chemical Constituents .......................................................................... 54
5.
Calibration and Validation................................................................................................. 57
5.1 Introduction .......................................................................................................... 57
5.2 Calibration and Validation Approach.................................................................. 58
5.3 Algorithms and Radiative Transfer ..................................................................... 60
5.4 Ground-based Observations............................................................................... 60
5.5 Validation of Trace Gases ................................................................................... 64
5.6 Scientific Analyses............................................................................................... 65
5.7 Principles and Recommendations for Calibration and Validation ................... 66
5.8 Implementation Strategy ..................................................................................... 67
6.
Recommendations............................................................................................................. 69
6.1 Introduction .......................................................................................................... 69
6.2 Algorithms and Calibration ................................................................................. 71
6.3 Implementation .................................................................................................... 72
6.4 Recommendations for Additional Space-Borne Measurements....................... 74
6.5 Advisory Body for the Ozone Project ................................................................. 75
6.6 Concluding Remarks ........................................................................................... 76
i
Annex A: Lists of Scientists and Experts Consulted ............................................................. 77
Annex B: Tables of User Requirements .................................................................................. 81
Annex C: The Data Records of Regularly Reporting Ground-Based Ozone Stations........ 101
Annex D: Examples of Airborne Research Campaigns........................................................ 109
Annex E: Other Space-Based Instruments ........................................................................... 117
Annex F: Acronym/Abbreviation List .................................................................................... 125
ii
iv
EXECUTIVE SUMMARY
Introduction
CEOS and WMO recognize the need for better integration of the major satellite and
ground-based systems to provide highly accurate, global environmental observation of the
atmosphere, cryosphere, oceans and land in a cost effective fashion. To satisfy this objective, a
framework for compiling user requirements, coupled with an overarching strategy for making
global observations is the goal of the new IGOS (Integrated Global Observing Strategy), set up by
a number of international bodies including WMO and Space Agencies. This report is a
contribution to the international effort. It proposes the better integration of the various systems
used to monitor ozone, including related key atmospheric parameters, and will contribute to the
objectives of the IGOS within a general IGOS theme on atmospheric chemistry.
This will assure the most effective use of available resources for global observations,
although priorities must be established for upgrading existing and/or establishing new systems
and provide a framework for decisions to ensure:
•
•
the long term continuity and spatial comprehensiveness of key observations
the research needed to improve understanding of Earth processes so that observations
can be properly interpreted.
The project will build upon existing and planned international global observation
programmes (e.g. METOP, NPOESS, WMO-GAW and NDSC) and identify deficiencies in the
current and planned systems. This report and its recommendations were compiled by a collection
of clients, space agency representatives and a cross section of experts and specialist in
atmospheric research. The list of contributors to this report and their institutions appears in Annex
A
The Ozone Project aims to develop the foundations of an integrated ozone measurement
strategy. This strategy reflects the need to understand variations of ozone in the troposphere and
stratosphere because of the central role the gas plays in several major environmental problems:
•
•
•
•
total column ozone is a controlling factor in determining levels of biologically damaging
ultraviolet radiation reaching the Earth’s surface;
ozone is an oxidising pollutant that is harmful to humans, animals and vegetation and
degrades man-made materials;
ozone is an active component of tropospheric and stratospheric photo-chemistry;
ozone is a “greenhouse” gas that contributes to the Earth’s radiative balance.
The project covers primarily the observational requirements associated with the "Montreal"
Protocol of the Vienna Convention. One of its specific objectives is to document the requirements
for observations of ozone and associated parameters needed to properly interpret the ozone
observations. These are then reviewed in the light of provisions for data acquisition with the focus
on the observing community and the steps needed to meet user requirements. The project
recognises the need and existence of appropriate numerical chemical and transport models used
to interpret the observations.
Grateful acknowledgement must be made to the many scientists and institutions (listed in
Annex A) who have contributed to the production of this report both by participating in the
workshops and by written contributions. Without this support the production of this report would
not have been possible.
v
Requirements
The Ozone Project has compiled a list of user requirements from the scientific community
1
(WMO-GAW, SPARC, IGAC) and existing measurement programmes from space and the ground
have been documented. From an analysis of the provisions and requirements, a set of
recommendations for establishing an integrated global ozone observing system is proposed. This
strategy distinguishes measurements that are needed continuously from those that are only
needed occasionally. A well supported and on-going validation programme coupled with a data
quality control programme is essential. As data sets improve, planning for the reprocessing and
the distribution of data is a major objective.
In addition to ozone itself, an array of chemical species and other geophysical parameters must be
observed. These include long lived source gases, reservoir species, radicals and several closely
associated meteorological variables such as temperature and winds to at least the same spatial
and temporal resolution as the gases. Aerosols play an increasing role in the stratosphere and
troposphere for chemistry and climate research so their characteristics must also be measured. In
addition, the total and spectral solar irradiances must be observed in order to be able to interpret
climate and ozone changes.
Available and Planned Measurements
A broad range of operational and research observations are underway and are planned
from both space and the ground. Data from Nimbus, TOMS, SAGE, SBUV/2, UARS, ERS-2,
WMO-GAW and NDSC, as well as many aircraft and balloon missions, have led to an improved
understanding of relevant atmospheric processes and provided a baseline for assessing needs for
future data sets. Research missions such as ENVISAT, EOS-Terra and EOS-Aura, and
operational missions such as METOP and NPOESS, will provide platforms to ensure the
continuation of baseline measurements though they only partially satisfy the requirements. A
major concern is the provision of data in the longer term (after the ENVISAT/EOS-Aura era) when
only those from METOP and NPOESS will remain available.
TOMS type data sets are assured (though not TOMS itself) through EOS – Aura, but there
is a potential gap between EOS-Aura and NPOESS until the advent of NPOESS which will
continue these measurements. Follow-on SAGE missions are assured although the exact
platforms are at this time somewhat uncertain. UV-VIS-NIR backscatter measurements will
continue with GOME-2 on METOP. GCOM and follow-on ADEOS will also provide collaborative
data from space. The ODIN, ACE and SABRE research missions will compliment the larger
research and operational missions. To date chemistry measurements have been made from low
Earth orbit, but upcoming missions must take advantage of new strategic orbits such as the
geostationary and L1 orbits to observe short term diurnal variations.
Ground observations (surface, balloon, and aircraft) must continue and be expanded to
provide correlative and validation data for the satellite missions as well as conducting essential
research observations. The networks such as NDSC and GAW (e.g. ozone sondes,
Dobson/Brewer and in-situ source gas observing stations)need to continue to provide data as part
of a better integrated system. Aircraft missions should continue to conduct extensive campaigns
to study processes with high spatial resolution. The commercial airlines also have a role in
providing platforms for routine observations (e.g. MOZAIC).
Calibration and Validation
Another major concern is the continuation and consolidation of calibration and validation
activities as these are critical to assure the scientific value of observations. They are essential for
deriving climate quality data sets. The space faring nations have and must continue to allocate
resources for the calibration and validation of Earth science missions. Both Europe and the United
States are now planning operational satellite systems that will carry ozone sounders to extend the
vi
long term record already produced by national research and operational missions. Japan is also
committed to fly atmospheric chemistry missions.
However, despite the fact that the major space agencies have embarked on these
missions, no concurrent long term validation programme is being planned nor is there any
assurance that the existing ground-based infrastructure will be in place when it is needed. Satellite
systems can only meet the established requirements if they are supported by correlative data of
known quality and continually challenged by reliable ground-based observations and quantitative
science.
Based on the experience gained from past satellite missions, an end-to-end approach for
calibration/validation, supported by a fully integrated global observing system including both
ground and space-based elements, must be established. For satellites this approach includes the
internal calibration programmes, post-launch calibration employing on-board systems, external
validation programs using highly controlled correlative measurements, subsequent algorithm
refinements and scientific analyses of the data to ensure consistency with the best understanding
of atmospheric processes and conditions. This is of particular importance given the existence of
parallel streams of the national missions, e.g. the European METOP and the US NPOESS ozone
instruments.
Recommendations
As discussed above, many of the identified requirements will be met by the existing and
planned measurements from ground and space. However, there remains the problem of a lack of
formal co-ordination among the space faring nations to optimise the deployed systems and to
assure compatibility for international users. In addition, there must be formal recognition and
support for the international community who are providing critical data from ground-based systems
for the calibration and validation of the space-borne systems.
The recommendations contained in the report (Chapter 6) make specific proposals for
remedying the missing components of the upcoming systems. They also describe improvements
that are required in existing systems and current procedures. The following is a summary of these
recommendations:
•
•
•
•
•
•
•
•
•
Establish a co-ordinated validation activity that extends over the entire lifetime of
satellite sensors that encompasses all elements of the IGOS system and takes
maximum advantage of concurrent national validation activities.
Extend the coverage of ground-based (WMO-GAW and NDSC) systems particularly in
the tropics and the Southern Hemisphere and designate a carefully selected subset
thereof as permanent, long term ground "truthing" facilities.
The space agencies that require validation data must provide sustained support for the
ground networks to insure data availability and quality.
Improve and/or provide additional measurements resulting from a survey of existing
and planned measurements. There is a particular need for measurements in the lower
stratosphere and troposphere.
The validation process is iterative and resources for reprocessing data must be made
available to ensure that users have access to the highest quality data.
Standardise data formats and encourage the synergistic use of data supported by
accessible archives and proper provision for reprocessing.
Improve national radiometric standards and sensitise the user community to calibration
issues.
Encourage international co-operation in the development of algorithms employed by
similar instruments and pool knowledge of radiative transfer physics.
Establish a body of scientists, engineers and managers to provide technical support to
funding agencies to ensure compatibility and completeness of the systems.
vii
There is also a practical incentive for swift action. Several satellite missions with ozone
instruments on board are scheduled for launch during this decade. The recommendations in this
report attempt to co-ordinate these missions and to remedy those areas that remain deficient in
the present and planned observing systems. Data collected following this approach will have the
necessary quality to enable the state of the atmosphere to be reliably monitored and changes
understood, thereby providing a basis for formulating sound environmental policies.
viii
MILESTONES IN THE HISTORY OF OZONE
1839
Discovery of the ozone as a permanent atmospheric trace gas by C.F. Schonbein.
1860
Surface ozone started to be measured at hundreds of locations.
1880
Strong absorption band of solar radiation between 200 and 320 nm attributed to upperatmosphere ozone by Hartley.
1913
Proof from UV measurements that most ozone is located in the stratosphere.
1920
First quantitative measurements of the total ozone content.
1926
Six Dobson ozone spectrophotometers are distributed around the world for regular total
ozone column measurements.
1929
The Umkehr method for vertical ozone distribution is discovered and determines the
ozone maximum is lower than 25 km.
1930
Photochemical theory of stratospheric ozone formation and destruction based on
chemistry of pure oxygen.
1934
Ozone sonde on balloon confirms maximum concentration at about 20 km.
1955
Global network of ozone stations proposed for the International Geophysical Year (IGY).
1957
WMO establishes standard operating procedures for uniform ground-based ozone
observations and the Global Ozone Observing System (GOOS) established.
1964
First ever satellite for total ozone measurement launched by US Department of Defense.
1965
Photochemical theory of ozone with destruction by HOx radicals.
1966
First total ozone measurements from satellites.
1971
Ozone destruction by NOx mechanism proposed.
1974
First consideration of CIOx chemistry as an ozone-destroying mechanism.
1974
Human-produced CFCs recognized as source of stratospheric chlorine.
1975
WMO conducts first international assessment of the state of global ozone.
1977
Plan of Action on Ozone Layer established by UNEP in collaboration with WMO.
1978
NASA’s Nimbus-7 launched carrying ozone and other atmospheric instruments
1981-98
Scientific assessments of the state of the ozone layer issued in 1981, 1985, 1988, 1991,
1994, and 1998 by WMO in collaboration with UNEP and national research agencies.
1982
The US’s NOAA commits to operational stratospheric ozone monitoring on polar
orbiting satellites (POESS followed by NPOESS).
1984
NASA-SAGE I: Stratospheric ozone profile measurements through solar occultation.
1984
Unusually low (-200 m atm cm) total ozone at Syowa, Antarctica, in October 1982, first
reported at the Ozone Commission Symposium in Halkidiki, but its significance was
recognized only the next year.
1985
Vienna Convention for the Protection of the Ozone Layer concluded and data from
Halley station on the existence of an ozone hole during Antarctic springs since the early
1980s published by the British Antarctic Survey.
1985
NASA’s Nimbus-7 TOMS maps Antarctic ozone whole which covers 10-20 millon square
kilometers
1983
Analysis of Montsouris (Paris) surface ozone (1873-1910) indicates levels then were
less than half of the present.
ix
1984
Montreal Protocol on substances that deplete the ozone layer concluded under UNEP
auspices and basic assessment of the state of the ozone initiated by the International
Ozone Trends Panel.
1985
Decrease of ozone concentrations by –10 percent per decade in the lower stratosphere
documented; proof from NASA Antarctic Campaign that active chlorine and bromine
byproducts of human activities are the cause of the Antarctic-spring ozone hole.
1990
London amendment to strengthen the Montreal Protocol by phasing out all CFC
production and consumption by 2000.
1991
The WMO/UNEP Ozone Assessment – 1991 reveals ozone is declining not only in
winter-spring, but all year round and everywhere except over the tropics; very large
concentrations of CIO measured in the Arctic confirms concerns for potential stronger
ozone decline.
1991
NASA’s Upper Atmospheric Research Satellite launched
1991
Quantified global and seasonal column ozone trends from TOMS.
1992
Copenhagen amendment further strengthened Montreal Protocol by phasing out CFCs
by the end of 1995, adding controls on other compounds.
1992-94
Extremely2 low ozone values (-100 m atm cm) during Antarctic spring and largest area –
24 m km covered; also the lowest ever ozone values measured during the northern
winter-spring seasons indicates increasing destructive capability by increasing chlorine
and bromine concentrations in the stratosphere.
1998
WMO/SPARC/IOC/GAW assessment of trends in the vertical distribution of ozone using
SAGE, balloon, and umkehr data.
1998
Europe’s Eumetsat commits to operational ozone monitoring
1995
Nobel Prize for work on catalytic chemical destruction of ozone by Molina, Rowland,
and Crutzen
1995
European Space Agency launches first mapping hyperspectral instrument (GOME) on
ERS-2 to measure atmospheric composition
1995
Record low ozone values (exceeding 25 percent below long-term average) observed
January to March over Siberia and a large part of Europe.
1996
Complete ban on industrial production of CFCs
1996
Japan launches the ADEOS series and plans follow on GCOM missions to measure
ozone and atmospheric chemistry
1996
CEOS initiated IGOS “The Ozone Project” as one of six pilot projects
1997
First Limb-scatter measurements of ozone throughout the Stratosphere from Space
Shuttle.
1998
Upper Atmospheric Research Satellite measured chlorine amounts
stratosphere leveling off resulting from Montreal and follow on protocols
2000
WMO/CEOS Report on a Strategy for Integrating Satellite and Ground Based
Observations of Ozone
x
in
upper
1.
1.1
INTRODUCTION
The IGOS Strategy
The IGOS (Integrated Global Observing Strategy) is intended to combine data from major
satellite, airborne and ground-based systems to provide global environmental observations of the
atmosphere, the cryosphere, the oceans and the land in a cost effective fashion. A fundamental
issue for IGOS is the identification of what it can contribute that cannot be achieved through
existing national and international mechanisms. In short the added value of IGOS has to be
demonstrated.
To satisfy this objective IGOS must provide a framework for the formulation of a coherent
set of user requirements to which providers can respond. It must formulate an overarching
strategy for global observations, allowing those involved in their collection to improve their
contributions and to make better decisions on the allocation of resources to meet priorities, taking
advantage of better international collaboration and co-ordination.
To facilitate the most effective use of available resources for global observations, priorities
need to be established for upgrading existing and/or establishing new systems. IGOS must
therefore provide a framework for decisions intended to ensure:
•
•
the long term continuity and spatial comprehensiveness of key observations;
the scientific research needed to improve understanding of Earth processes so that
observations can be properly interpreted.
It must build upon the strategies of existing international global observation programmes
focusing additional efforts in areas where satisfactory international arrangements and structures
do not currently exist. It should aim to exploit international structures that successfully contribute to
current provision of global observations, rather than create a new centralised decision making
organisation. The unnecessary duplication of observations must be avoided.
IGOS is intended to help provide governments with improved understanding of the need for
global observations and the deficiencies of current systems. Allied with this, opportunities must be
identified for capacity building, assisting countries to obtain the maximum benefit from the total set
of available observations. Situations where existing international arrangements for the
management and distribution of key global observations and products could be improved must be
identified.
IGOS also seeks to stimulate the creation of improved high level products by facilitating the
integration of multiple data sets from different agencies and national and international
organisations. It assists the transition of systems from research to operational status through
improved international co-operation.
In striving to respond to these principles, contributions to IGOS should help ensure:
•
•
•
the long term continuity of measurements of key variables;
adequate archiving and access capability for all data sets;
consistency of data quality even when there are disturbances in the data record, e.g.
due to new technology;
• an active and co-operative validation programme extending over the entire life of the
satellite sensor or measurement system to ensure the integrity of the space-borne
data:
• sufficient ancillary data to enable users to judge the data quality and to properly
interpret the results.
Within this overall context the Committee for Earth Observation Satellites (CEOS) decided
to establish six Pilot Projects to assess the feasibility of achieving the objectives of IGOS. One of
1
these was the Ozone Project which is the subject of this report and which includes observational
requirements arising out of the Montreal Protocol of the Vienna Ozone Convention .
1.2
The Ozone Project
Knowledge of the amount and distribution of ozone (and changes in total levels) in the
Earth’s troposphere and stratosphere is important because of the central role ozone plays in
several important environmental problems:
•
First, ozone, through its absorption and emission of solar and terrestrial radiation,
contributes significantly to atmospheric temperature structure and the radiative forcing
of the troposphere-stratosphere system.
•
Secondly, the total column amount of ozone in the atmosphere is a major factor in
determining the amounts of biologically damaging ultraviolet radiation that reach the
Earth’s surface, as well as the photochemistry of the troposphere.
•
Thirdly, near the Earth’s surface ozone is an oxidising pollutant which is harmful to
humans, animals and vegetation as well as contributing to the degradation of manmade materials. As such it influences much of the photochemistry that occurs in the
troposphere.
Knowledge of the distribution of ozone is also important to the operational meteorological
community both through its role as a contributor to the Earth’s radiative balance and through its
use as a motion tracer. Advances in meteorological modelling are demonstrating that the inclusion
of ozone can lead to improved weather and climate forecasts and, as a result, ozone is beginning
to be assimilated in meteorological models. Operational agencies are also increasingly being
asked to predict levels of ultraviolet radiation reaching the surface; knowledge of ozone amounts is
essential for this purpose.
Changes in the distribution of ozone in response to human activity have been anticipated
for some time and over the past decades such changes have actually been observed. Figure 1
(from NASA's Goddard Space Flight Center) illustrates predicted and TOMS measured global
ozone trends. Predictions indicate a recovery in the near future, however these must be
confirmed with measurements with TOMS-like precision. The predicted changes in ozone
distributions are due to several factors. Emissions of industrially-produced chlorine (Cl) and
bromine (Br) containing molecules into the atmosphere lead to destruction of ozone in the
stratosphere due to the catalytic properties of chlorine and bromine. In addition, there are natural
sources of bromine in polar regions that may also contribute to the catalytic destruction of ozone.
Emissions of nitrogen oxides, hydrocarbons, and carbon monoxide change the photochemistry of
ozone in the troposphere and increased emissions of these species, associated with human
activity (burning of fossel fuels and biomass), have led to increases in tropospheric ozone
amounts. Evolutions in climate also have the potential to change both tropospheric and
stratospheric ozone in ways that are complex and not yet well understood.
In addition to the most spectacular such effect, namely the seasonal decrease in total
ozone which takes place over Antarctica every spring (with the near-total removal of ozone in
some altitudes), there has been a gradual decrease in total ozone amounts over much of the midlatitudes. Most recently, there have been some significant instances of late winter/spring-time
ozone depletion in the Arctic (most markedly in the winter of 1996-7). Satellites and balloons have
shown that while most of this decrease has taken place in the lower stratosphere, there have also
been some important decreases in ozone levels in the upper stratosphere. Figure 2 (from KNMI)
illustrates very low ozone amounts over high latitudes of the Northern Hemisphere during for
April1997, as observed by GOME. Normally ozone near the pole reaches a maximum value at this
time
2
Figure 1: Measured and Predicted Ozone Trends
(Courtesy, Goddard Space Flight Center)
Figure 2: Northern Hemisphere Assimilated Total Ozone (Courtesy, Royal
Dutch Meteorological Institute)
3
Most of these changes have been attributed to long term increases in the concentrations of
halogen-containing source gases whose breakdown products can destroy ozone through rapid
catalytic processes. The decrease in ozone amounts in the lower stratosphere coupled with
increases in greenhouse gases, have led to small but significant decreases in temperatures in the
lower stratosphere over much of the Earth. These are amongst the most significant temperature
changes that have been attributed to human activity. The ozone-temperature linkage in the
stratosphere is therefore a critical one and detailed understanding of the feedback between
changes in these two quantities is a priority.
At the same time that ozone levels have been decreasing in much of the stratosphere,
there has been an increase in ozone amounts in much of the troposphere stemming partly from an
increase in combustion activities at the surface of the Earth, including both fossil fuel combustion
and biomass burning. However, tropospheric ozone concentrations are much more variable in
composition than the stratosphere with some regions showing increases in ozone levels while
others do not. Increases in tropospheric ozone, especially in the radiatively important upper
troposphere, can have a significant impact on radiative forcing and must therefore be considered
in studies of climate forcing and atmospheric response. Figure 3 (from the Harvard University
GEOS-CHEM model) illustrates calculations of monthly mean afternoon surface ozone
concentrations (1 - 4 p.m.) in July. Particularly noteworthy is pollution over industrial areas in the
US, Europe and Asia, with enhancements in Asia due to burning. Satellite observations are
needed to provide a global perspective of regional to intercontinental transport of pollution
phenomena.
Figure 3: Modelled Global Distribution of Surface Ozone
(Courtesy, Harvard University)
4
A problem peculiar to the tropopause region is that of emissions from aviation. Aircraft
emit particles and gases affecting ozone, methane, and cloudiness. The emissions from aircraft
are released directly into the free troposphere and lower stratosphere. At present the impact of
NOx emissions on ozone formation near the tropopause and methane reduction and subsequent
climate effects can be quantified only with large uncertainties. In addition, the chemical and
radiative effects of contrails and cirrus clouds, and the role of water vapour emissions in the
stratosphere are far from being understood. The relative climate impact of these emissions
compared to that of CO2 has to be determined as prediction of the impact of aviation is currently
limited by the general understanding of air chemistry, cloud physics and related processes.
Changes in the ozone profiles (in both the stratosphere and troposphere) can also have
implications for global tropospheric chemistry because changes in levels of stratospheric ozone
can affect the ultraviolet radiation flux into the troposphere which, together with ozone itself, is
responsible for much of the photochemistry that takes place in this region of the atmosphere. In
part, this photochemistry produces hydroxyl, a free radical that initiates the decomposition of many
trace gases in the atmosphere as well as the formation of some types of aerosol particles.
In parallel to these changes in ozone amounts and distribution, there are evolutions in the
physical state of the atmosphere. The increases in carbon dioxide and other radiatively active
gases are altering the temperature structure of the atmosphere which, over the longer term, may
be associated with significant changes in the nature of the meteorological processes that occur in
the troposphere, as well as in the properties of the tropopause region and the dynamical coupling
between the troposphere and stratosphere. These can affect the transport of energy and
momentum within the entire global atmospheric system together with the transport of ozone, its
photochemical precursors and the agents of its catalytic destruction. Temperature changes will
also directly affect the rates of chemical reactions involved in ozone photochemistry.
Any long term changes in the structure and dynamics of the tropopause regions could have
large impacts on the distribution of ozone in the stratosphere by changing, for instance,
stratospheric water vapour amounts, formation conditions for PSCs (polar stratospheric clouds)
and/or aerosols and the forcing of large scale stratospheric waves from the troposphere. Changes
in the region of the tropopause will also affect levels of tropospheric ozone as the flux of ozone
across the tropopause (from the stratosphere to the troposphere) is a major source of ozone to
the troposphere.
The ability of the scientific community to understand the observed changes in ozone and
predict future evolutions, especially in the context of an atmosphere whose physical state is
changing due to climate change, is critically dependent on the availability of comprehensive
models capable of properly simulating both the chemical and physical evolution of the atmosphere
and the linkages between the two. The further development of these models draws on both
advances in modelling capability and their critical evaluation and validation. For this the provision
of the broad range of representative and reliable observational data, considered in this report, is
essential.
1.3
Requirements and Data Sources
1.3.1 General Requirements
It is clear that knowledge of ozone concentrations and its distribution is of fundamental
importance given the pivotal role ozone plays in the climate system. Human-induced changes in
ozone levels combine to make the accurate long term measurement of ozone a priority for policy
makers as well as for the scientific and environmental communities. This places strict demands on
measurement systems as they have to be capable of characterising long term trends in the
presence of the very large variability that exists on several temporal scales.
5
These include diurnal cycles, day-to-day meteorological, seasonal and inter-annual (quasibiennial oscillation, El Niño/Southern Oscillation, North Atlantic Oscillation) variability as well as the
11-year solar cycle and sporadic events such as volcanic eruptions and solar proton events. It
must also be possible to accurately differentiate between changes in ozone and those of other
atmospheric parameters (e.g., temperature, aerosol loading) that may affect its direct
measurement or retrieval via remote sensing techniques.
Furthermore, full global coverage is essential so the measurement system addressing
these needs must be able to observe from the tropics to the poles. Moreover, as changes in the
stratosphere and troposphere may be quite different (indeed of opposite signs), the accurate
characterisation of both regions as well as their combined effect, is essential.
To interpret observed changes in ozone it is not enough to measure ozone alone. In
addition to ozone itself, several atmospheric chemical species, meteorological (including aerosol)
and solar parameters must also be observed. Without such information it will be difficult to
understand why observed changes are taking place, making it impossible to forecast future
developments and hence to assess the effectiveness of proposed (or current) control measures.
For some applications, such as the prediction of the levels of ultraviolet radiation at the Earth's
surface, the use of ozone data will be inadequate unless accompanied by knowledge of other
quantities such as the distribution of aerosols, clouds and their respective optical properties.
This means that three general groups of parameters will have to be measured, namely
ozone itself, several closely associated meteorological variables and a number of chemical
parameters. These are summarised in Tables 1.1 and 1.2 which list the various geophysical
variables separated according to the above criteria. Table 1.1 also indicates whether they are
observed by current systems, classifying them into one of three subgroups, namely:
•
•
•
source gases - species having long lifetimes; typically produced by biological and/or
industrial processes at the Earth's surface;
reservoir species - species having intermediate lifetimes; typically formed in the
atmosphere as a result of the breakdown of source gases, although some are directly
emitted from the Earth's surface;
free radicals - species having unpaired electrons and short lifetimes; often formed
photochemically from source gases or reservoir species.
In addition, meteorological information (such as temperature and winds) is needed to set
the observations into a proper context and, in some cases, for inclusion in the algorithms used to
derive concentrations of trace constituents from observed radiances.
In compiling the lists of user requirements for observations of chemical species throughout
the atmosphere it is important to recognise the breakdown between the different classes as
summarised in these two tables. A distinction is made between parameters whose distributions
need to be measured regularly over long periods of time over a broad range of geophysical
conditions (Table 1.1), and those whose concentrations only need to be measured on either a
limited number of occasions (though over a similarly broad range of geophysical conditions) or
regularly but at a limited number of locations (Table 1.2). As far as this report is concerned the
former are classified as being of primary importance and are the only ones considered further in
this document. In this report, carbon dioxide and other greenhouse gases were considered only
with regard to their direct or indirect relevance to ozone so there is no detailed discussion of
measurement requirements arising as a consequence of the Kyoto Protocol.
6
Table 1.1: Parameters which must be observed regularly over long periods of time over a broad range of
geophysical conditions
PARAMETER
CLASS
SURFACE
TOTAL
COLUMN
LOWER
TROP.
UPPER
TROP.
LOWER
STRAT.
UPPER
STRAT.
&
MESO.
O3
O3
O3
O3
Mon./Trends
Oper. Met.
Air Quality
UV Forecasts
A
A
A
A
A
A
N
A
A
A
Temp.
Wind
Tropopause
Cloud Tops
Met. Variable
Met. Variable
Met. Variable
Met. Variable
A
H2O
N2O
CH4
CO
CO2
Source Gas
Source Gas
Source Gas
Source Gas
Source Gas
A
A
A
A
A
HCl
HNO3*
Reservoir
Reservoir
A
BrO
ClO
NO2
NO*
Free Radical
Free Radical
Free Radical
Free Radical
N
N
A
A
Aerosol Pres.
Aerosol Char.
PSCs
Met. Variable
Met. Variable
Met. Variable
A
A
UV
Met. Variable
A
A
A
N
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
N
A
N
A
A
A
A
A
A
N
N
N
N
A
A
N
A
N
A
A
A
A
A
N
A
A
A
A
P
P
P
P
P
P
P
P
GBP
P
BBIS
P
P
S
S
S
S
Note * - not all of these are required everywhere; in some situations only one or two of them may be needed
Key
A = available
N = needed
GBIS = ground-based in-situ
BBIS = balloon-based in-situ
P = primary role
S = supporting role
GBP = ground-based profile
GBC = ground-based column
S
S
S
S
P
S
SBC
P
P
SBP
P
P
P
S
P
P
P
S
P
S
P
P
S
S
S
P
P
S
P
S
S
P
S
P
S
A
A
A
A
7
GBC
P
P
P
N
A
GBIS
P
P
S
A
A
AVAILABLE MEASUREMENT PLATFORM
P
P
P
S
P
P
P
S
P
P
S
P
P
S
P
P
S
SBC = space-based column
SBP = space-based profil
P
P
P
S
P
S
S
P
S
P
P
P
P
P
P
Table 1.2: Atmospheric trace species that only need to observed on either a limited
number of occasions (though over a similarly broad range of geophysical
conditions) or regularly but at a limited number of locations.
CLASSIFICATION
TRACE SPECIES
Source Gases
CFC-11, CFC-12, CFC-22, CH3Cl, CH3Br, H1201,
H1311, CF4, SF6,
Reservoir
HBr, ClONO2, HOCl, OClO, H2O2
Free Radicals
OH, HO2, NO3
1.3.2 Data Sources
To characterise the distribution of ozone and the associated parameters that affect it
(listed in Table 1.1), as well as their short and long term variations, the capabilities of groundbased, in-situ, airborne and space-based systems all have to be exploited. Each type of platform
should make an unique and complementary contribution to the overall data requirements. Thus,
surface-based in-situ systems observe the concentrations of long-lived source gases, whose
concentrations help drive both the chemistry and the radiative forcing of the atmosphere. Surfacebased remote sensing instruments can provide (often to very high accuracy and long-term
stability) estimates of column amounts (and in some cases vertical profiles) of both industriallyproduced source gases and their breakdown products, as well as of ozone, aerosols and radiation.
Balloon-borne instruments, especially ozone sondes, can provide unique, high vertical
resolution, information on the distributions of variables from the surface up through to the middle
stratosphere. They can also provide data below clouds which cannot be penetrated by most
space-based instruments. This is especially important in the tropics where a high tropopause and
persistent cloudiness frequently makes significant regions of the troposphere inaccessible to most
space-based systems. Airborne systems have similar capabilities though geographic coverage is
limited.
Generally, space-based systems can provide global coverage, coupled with accurate longterm observations of global distributions of many important parameters, as well as measuring the
solar radiation entering and leaving the Earth's atmosphere. These data are especially important
over uninhabited regions of the Earth (or over developing countries) where only limited surfacebased data are available. 4-D data assimilation is increasingly being used to optimise or derive
global distribution fields for a number of species.
More localised, process-oriented observations exploiting comprehensively instrumented
balloon-, aircraft- and space-based systems or exploratory satellites are also needed to
quantitatively test understanding of the chemical, meteorological and transport processes affecting
the distribution of ozone and related parameters. Currently models generally do an adequate job in
predicting ozone levels except in the lower stratosphere in the Northern Hemisphere at mid
latitudes where ozone is decreasing faster than model predictions. The results of such
experiments are important in helping to clarify and reduce requirements for data by extending the
capabilities of the models used to forecast future evolutions in ozone levels and reducing their data
requirements. The needs of such process studies are not considered in this report as they fall
outside the context of the Ozone Project (see next section).
8
1.4
The Objectives of the Report
To meet the scientific and user requirements in as cost effective and efficient fashion as
possible, it is essential to adopt an integrated global observing strategy, as set out in Section 1.
This involves the strategic combination of data from all observing systems (i.e. ground-based,
space-based etc.; in-situ and remote). To help establish this philosophy the Committee decided to
initiate a set of Pilot Projects one of which is the specific concern of this Report, namely the
provision of long term observations of ozone.
The CEOS therefore mandated a small group of scientists to produce a report on The Long
Term Continuity of Ozone Measurements to lay the groundwork for the formulation of a strategy
for atmospheric ozone and related parameters. The list of contributors and their institutions can be
found in Annex A. It should be noted that two workshops have taken place; one in Tokyo in July
1997 and one in Geneva in May 1999. During these meetings experts were asked to clarify
requirements and review the capabilities of current observing systems with the aim of highlighting
deficiencies and indicating possible courses of remedial action. These are the origin of the various
recommendations contained in this report.
Noting the specific objectives of the Ozone Project and in line with the arguments
presented in the previous section, it was decided to limit the list of variables (in addition to ozone
itself) to those strictly required either a) to properly interpret the ozone observations or b) for use in
the geophysical algorithms used to retrieve ozone distributions from space-based instruments.
Therefore, this is a climatological, as opposed to a process study, oriented project. This limits the
list of variables to be considered and hence the scope of the recommendations contained in this
report. The need for category b) variables will vary with the measurement technique.
Underlying this is an implicit assumption that the contributions of several relevant
unmeasured parameters can be calculated from the measured distributions of a relatively small
sub-set of parameters. This assumes the existence of appropriate numerical chemical and
transport models which must be tested against comprehensive data sets obtained by research
oriented balloon, aircraft and/or space-borne missions.
A further point to note is that not all the requisite variables need to be observed frequently
or globally. Those listed in Table 1.1 generally have to be observed frequently and globally over
the long term and quite often information on their vertical distributions is required. They are the
focus of this report.
For the reservoir and radical species listed in Table 1.2, it could be argued that once the
relationship between their distributions and those of their chemical precursors and/or related family
members (listed in Table 1.1) is well established (on the basis of observations), regular long term
measurements may no longer be required. It is assumed that the requirements to observe the
source gases listed in Table 1.2 can basically be met by ground-based systems though satellite
observations are required to ensure representative global coverage.
It is important to note that a number of the existing programmes have already been
specifically designed to make long term observations of ozone and related parameters including:
•
The ground-based Dobson/Brewer/Umkehr network for total ozone and ozone profile
measurements, as well as the other surface-based measurements associated with the
Global Atmosphere Watch (GAW) network of the World Meteorological Organization
•
The ground-based remote-sensing network of instruments associated with the
internationally sponsored Network for Detection of Stratospheric Change (NDSC)
•
Surface-based in-situ sampling associated with several nationally-operated (but
globally distributed) programmes (under the umbrella of WMO-GAW) designed to
determine surface-level concentrations of long-lived trace gases
The balloon-based ozone sonde network of the WMO-GAW and NDSC programmes
•
9
•
Operational space-based measurement programmes involving mainly the
US (TOM, SAGE and NPOESS) and Europe (ERS-2 and METOP), which include both
long term measurement programmes and multiple instruments on different platforms
sequentially in time.
In many instances requirements are likely to be met by access to these existing continuous
observing systems. It is also necessary to consider research programmes that are of sufficient
duration to be able to contribute to the aims of the Ozone Project. Here a measure of selection is
necessary as short term measurements, even if of high quality, cannot be expected to contribute
to the long term monitoring of ozone. Those that currently satisfy this selection criteria include
ENVISAT and EOS-Aura.
In considering the development of a measurement strategy addressing the objectives of
the Ozone Project the report recognises that the first priority for the use of the data is for
climatological purposes, namely to assess and predict changes the Earth’s radiative balance and
the amounts of ultraviolet radiation reaching the Earth’s surface arising from changes in the
concentration and distribution of ozone. The primary concern is the role of ozone as an indicator of
the net effect of a complicated set of chemical and dynamical processes, the exact details of which
may be changing with time due to human activity.
These data also have major applications towards air quality research and monitoring and to
meteorological models, especially in the context of the assimilation of ozone in such models. It is
recognised that developing interest in these additional uses, especially in meteorological data
assimilation, is likely to require that more consideration be given to the implications of this
increase, particularly on data continuity and time between observations and availability of
processed data.
10
2.
USER REQUIREMENTS
In considering requirements for global observations of ozone and related species, it is
important to be specific as the requirements can vary significantly from one set of users to another
with regard to spatial coverage, accuracy, etc. User requirements (like the capabilities of any
measurement system) vary significantly with height, so it is necessary to link requirements to
altitude. In all cases the interest of the user is in end-to-end system performance set in the context
of an integrated global observing system.
2.1
Sources of Information and Definitions
The requirements presented in this report are derived from those included in the "User's
Requirements Data Base" prepared by the World Meteorological Organization and the report of
the ad-hoc Global Climate Observing System (GCOS) Atmospheric Chemistry Panel meeting
(Toronto, Canada, May 23, 1997). They were reviewed by participants at the initial meeting for the
CEOS Ozone Pilot Project held in July, 1997 in Tokyo, Japan and during the Ozone Project
Consultative Workshop held in May, 1999 in Geneva, Switzerland. The views of SPARC and IGAC
have also had a strong bearing on the compilation of the requirements.
Two levels of requirements have been derived for each parameter, namely:
•
•
The "target" set of requirements - defined as the set of requirements that satisfy the
needs of most (if not all) of the user community.
The "threshold" set of requirements – defined as the minimum set of requirements
which satisfy the needs of at least one set of users.
A system that did not meet the threshold requirements would be very difficult to justify but,
on the other hand, to attempt to fully satisfy the target requirements is often unrealistic. Thus, this
report (notably Chapter 4) mainly focuses on threshold requirements.
In generating the tables (see Table 2.1 and Annex B) which summarise the requirements
great reliance has been placed on "quantitative science", i.e. on measured concentrations, on
published trend assessments and on known concentration differences in the vertical and horizontal
distribution of the stated parameters. The target values are derived from user observation criteria
(as used in atmospheric chemistry, trend analyses, etc...) and substantiated by "local"
observations which exploit the best available technology. This means that, based on anticipated
performance and target and threshold values, the benefits associated with the deployment of
specific systems will be identifiable.
Since requirements vary with height, it is logical (albeit a little controversial) to link and
thereby generalise them to some broad pressure/altitude regimes, notably:
• Total Column
• Lower Troposphere
• Upper Troposphere
• Lower Stratosphere
• Upper Stratosphere and Mesosphere
0 to 5 km
5 km to Tropopause
Tropopause to 30 km
> 30 km
11
Table 2.1: Target and threshold requirements for ozone (O3 ) - greenhouse gas, ultraviolet shield and air pollutant. Target
requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy the needs of
at least one user group.
Thresh
Target
Thresh
Target
Thresh
Target
Thresh
Target
Thresh
Target
TREND
DETECTION
(WITH
CONTINUITY)
% per year
Lower
Troposphere
250
<10*
5
0.5
20%
or 4 ppb
3%
or 1 ppb
30%
or 6 ppb
5%
or 2 ppb
168
3
0.5
Upper
Troposphere
250
50
5
0.5
20%
or 4 ppb
3%
or 1 ppb
30%
or 6 ppb
5%
or 2 ppb
168
3
0.5
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
250
50
3
0.5
15%
or 100 ppb
3%
or 20 ppb
20%
or 150 ppb
5%
or 40 ppb
168
3
0.3
250
50
6
0.5
15%
or 75 ppb
3%
or 20 ppb
20%
or 100 ppb
5%
or 30 ppb
48
3
0.3
Total Column
100
10
-
-
5%
or 6 DU
1%
or 3 DU
5%
or 6 DU
1%
or 3 DU
24
6
0.1
Total Column
(Troposphere)
100
10
-
-
15%
or 6 DU
5%
or 3 DU
15%
or 6 DU
5%
or 3 DU
24
6
0.5
REGION
HORIZONTAL
RESOLUTION
(KM)
VERTICAL
RESOLUTION
(KM)
RMS ERROR
(BY VOLUME)
Note * - Lower range due to air quality user/process study requirement
12
BIAS ERROR
(BY VOLUME)
TEMPORAL RES.
(OBSERV
CYCLE; HRS)
2.2
Relationships between Applications and Requirements
To illustrate the way requirements vary with application and to set the scene for the listing
of requirements, some of the principal applications for the ozone data are discussed in this
section. The focus of this report is on ozone, reflecting its central role in atmospheric chemistry
and the atmosphere's radiative balance. However, requirements are also established for related
chemical and meteorological parameters which are either required to help interpret ozone
observations or else for use in the derivation of relevant geophysical variables (see Chapter 1).
Table 1.1 provides a list of all the variables considered in this report.
2.2.1 Climate and Radiation
The radiation balance (and hence climate variability) is very sensitive to variations in the
concentration of ozone with height so vertical resolution can be important, especially in the upper
troposphere/lower stratosphere where vertical gradients can be quite steep. This means that for
investigations into climate variability (and radiation balance) vertical profiles of ozone are also
required. For work on radiation balance this must be coupled with an horizontal resolution
compatible with that used in models (though this is not a critical issue for the study of ozone
trends).
In the stratosphere, above the peak of the ozone layer, the requirements placed on vertical
resolution are generally less severe as gradients tend to be smaller. However, the ability to make
measurements over fairly narrow latitude ranges is important as fairly strong horizontal gradients
can exist across some of the so-called atmospheric "transport barriers" (e.g. polar vortex/midlatitudes, mid-latitudes/tropics).
The same is true of water vapour (and some other variables) for which tropospheric and
stratospheric amounts are usually very different (though in the opposite sense to ozone for which
amounts are higher in the stratosphere and lower in the troposphere, while the converse is true for
water vapour). Therefore, the ability to observe rapid changes in mixing ratios with altitude is
essential. For many purposes (the same is true for ozone) long term measurement accuracy and
precision is important so if multiple instruments are used there must be good consistency between
them.
For its use in long term studies of surface ultraviolet radiation, the main requirement placed
on observations of ozone column amounts is the combination of quite high horizontal resolution
with good precision and long term stability, i.e. minimal instrumental drift. Where a network of
instruments is used this means that the absolute calibration of each instrument must be high
enough to ensure there are no unknown station-to-station biases.
Measurements must span a range of solar zenith angles and should be valid in the
presence of clouds (especially broken clouds) and aerosols. In many cases, for the data to be
quantitatively useful in calculating surface ultraviolet fluxes, information on these potential sources
of interference will be required. For this, daily coverage of the sunlit Earth is almost a prerequisite.
Although, the data must be of high quality, delivery times for trend and climatological
studies can generally be quite slow. However, the use of ozone column data in forecasting levels
of surface ultraviolet radiation and other meteorological applications presumes the existence of a
capability for rapid delivery and processing. This is in line with the need to ensure the rapid
turnaround of visual descriptions of the total ozone field, especially during times of significant
ozone depletion in the Antarctic and the Arctic.
2.2.2 Meteorological and Other Applications
Ozone data in the stratosphere and around the tropopause are finding increasing use in
operational meteorology. The assimilation of ozone observations into numerical meteorological
13
models helps to consolidate information on atmospheric motion and the characteristics of the
tropopause region. For this application the real-time or near real-time delivery of data is essential.
For the moment the main focus is on total column amounts but the need for information on vertical
profiles can also be anticipated.
Near the tropopause ozone amounts vary significantly with atmospheric structure. Valuable
insights into the evolution of meteorological situations can be obtained by examining ozone data.
These data can also be used in combination with information on the presence of clouds and
aerosols to forecast surface ultraviolet radiation and to help establish boundary conditions for
tropospheric air quality forecasts. Other data, which are typically obtained along with ozone data
(notably observations of aerosols, in particular those of volcanic origin), may serve as the basis for
advice on how to avoid hazards or to improve estimates of radiative balance (essential for long
term forecasting). For all these applications the rapid delivery of data is essential.
Ozone is also one of the key parameters when considering air quality in the lower
troposphere. For this both high precision and long term stability are essential if the significance of
both spatial and temporal variations in measurements is to be established. Air quality
programmes require knowledge of the distribution of ozone at the surface and as a function of
altitude in the lower and middle troposphere. Knowledge of the concentrations of key ozone
i
precursors (e.g. carbon monoxide, nitrogen oxides and hydrocarbons) and radiation levels [J(O D)
and J(NO2)] is essential.
Pollution events have strong daily variations therefore diurnal variations of ozone and its
precursors must be made available in near-real time. In regions for which there can be variable
contamination from human activity, higher measurement frequencies are required to help
characterise the relative contributions of polluted and unpolluted air masses. Where data are used
for trend and climatological studies, its rapid availability is not of critical importance, but if they are
to be used to check compliance with air quality standards or to forecast air quality, rapid availability
is again a priority. Profile information separating the boundary and the free troposphere is
essential.
2.3
The Requirements
In this section the detailed requirements are presented, largely in tabular form (see Annex
B). Table 2.1 for ozone and the tables in Annex B for other atmospheric parameters summarise
the requirements for data on surface level concentrations, total column amounts and vertical
profiles using the altitude regions (where applicable) defined in Section 2.1. In reviewing
measurement requirements for atmospheric trace constituents, it is helpful to follow the
classification introduced in Chapter 1 and to consider them as falling into one of three subgroups,
namely source gases, reservoir species or free radicals plus pertinent meteorological information
required to set the observations into a proper context or for use in retrieval algorithms.
Generally, requirements vary from parameter to parameter and from region to region. They
are less well established in the mesosphere than for other parts of the atmosphere. Thus,
requirements in these parts of the atmosphere should not be considered as drivers for determining
observation requirements. This is reflected in later chapters of this report where needs are
assessed against provisions.
For ozone, the primary quantity of interest in this document, detailed requirements are
provided in Table B.1 in Annex B. Tables B.2 detail the requirements for the "source gases" listed
in Table 1.1 (i.e. water vapour (H2O), nitrous oxide (N2O), methane (CH4), carbon monoxide (CO)
and carbon dioxide (CO2)); Tables B.3 the requirements for the "reservoir species" listed in Table
1.1 (i.e. hydrogen chloride (HCl); nitric acid (HNO3); Tables B.4 the requirements for the "free
radicals" listed in Table 1.1 (i.e. bromine oxide (BrO), chlorine monoxide (ClO), nitrogen dioxide
(NO2) and nitric oxide (NO)). Specific requirements for information on temperature and wind are
summarised in Tables B.5 and those for aerosols and polar stratospheric clouds in Table B.6.
14
2.3.1 Ozone (Table 2.1 and B.1)
Ozone plays a key role in atmospheric chemistry and the radiative balance of the
atmosphere. In the stratosphere it is the main absorber of ultraviolet radiation. This absorption is
responsible for the increasing temperature above the tropopause. In the lower stratosphere and
upper troposphere it becomes a powerful greenhouse gas and forcing function for climate change.
In the lower troposphere it is a pollutant and is created through complex chemical reactions with
anthropogenic gases and sunlight. This means that the observational requirements vary
considerably. Table B.1 attempts to satisfy most user requirements and to some degree it is a
compromise. Because of the key role ozone plays in this report a more detailed justification for the
table of requirements is provided below.
o
o
General circulation models currently use a grid size of 1 x 1 , i.e. a horizontal resolution of
about 250 km. This was set as the horizontal threshold. The horizontal target value for the lower
troposphere was set to 10 km based on the requirement of the air quality user community to
resolve the horizontal ozone gradient within and downwind of major population centres. Above the
planetary boundary layer the horizontal ozone concentration gradient is less pronounced allowing
a relaxation of the target value to 50 km. For the total column density, the threshold requirement of
100 km is based on the Dobson/Brewer user community constraining the representivity of their
vertical "point" measurement to about this value. However, a much higher horizontal resolution will
be required to fully meet user requirements; thus the target value of 10 km.
The target value of 0.5 km for vertical resolution meets the modelling community
requirement. Current regional climate and chemistry models which operate with vertical resolutions
of this order of magnitude and observations confirm that the vertical ozone gradient does change
significantly with altitude on this scale. Of particular importance to climate modellers are the ozone
changes in the 8-12 km range (where an increase in ozone is postulated) and in the 15-20 km
range (where a decrease in ozone concentration occurred). The values for vertical threshold
reflect the requirements of other user groups (air quality, climate and chemistry modellers, trend
analysts) who also need ozone profile information.
The target values for bias and RMS errors reflect the ozone concentrations observed within
the stated vertical regions of the atmosphere and the issues that the different user groups need to
resolve. For the troposphere, and particularly for the planetary boundary layer, the air quality
community routinely demands an accuracy of 5% or 2 ppb and a precision of 3% or 1 ppb (always
the larger of the two numbers).
For the lower stratosphere, several issues are important which have to be considered in
setting the target value, notably ozone increase due to air traffic (8-12 km), ozone destruction at
higher levels due to heterogeneous reactions (< 20 km), global ozone decrease due to CFCs and
ozone depletion in the Antarctic and Arctic regions. Since the ozone concentration above the
tropopause increases significantly (by an order of magnitude) to attain a peak value at about 20-25
km and decreases thereafter, different target and threshold requirements have been forwarded for
these altitude regimes by the user communities, reflecting their interest in specific scientific or
policy issues.
With about 90% of the total ozone residing in the stratosphere, the total trend in column
ozone is governed by changes in this region (mainly in the lower stratosphere). Between January
o
o
1979 and May 1994 total ozone (60 N to 60 S) showed a decline of 2.9% per decade.
Consequently the target value for total ozone (column) trend detection was set to 0.1 % per year
and for the lower/upper stratosphere to 0.3 % per year.
Ozone trends in the troposphere have been studied by many workers, but remain uncertain
in large regions of the globe due to the lack of reliable long term data sets. The atmospheric
chemistry user group required a target value of 0.5% for both planetary boundary layer and free
troposphere.
15
2.3.2 Other Chemical Species
a)
Source Gases (Tables B.2)
The presence of source gases (produced both naturally and by human activity) can have
significant impacts on the global atmosphere because of the radiative and chemical effects
associated with their presence, in particular their role in influencing the distribution of ozone. Their
long chemical lifetimes means that long term global measurements of a small number of them as
a function of altitude, are sufficient to provide insights into atmospheric transport as well as
providing a dynamical context for the measurements of ozone and other parameters. This means
that the accurate long term observation of some of these species is a critical requirement - the
most important of which is water vapour.
Surface level measurements will be the most critical for establishing long term variations in
the concentrations of many of these constituents which can evolve significantly with time but which
cannot be predicted with any certainty. Classes of compounds for which such measurements are
needed include halides and halocarbons from both natural and anthropogenic sources. Some of
these are included in Table 1.2.
The observation of the more chemically-active source gases are specified in this report and
are listed in Table 1.1. The justification for these observations are discussed below.
Nitrous Oxide (N2O) and/or Methane (CH4) - it is useful to monitor one or more of the long
life tracers to help clarify the dynamical context of the tropospheric air masses associated
with observations of trace species. Two of the most commonly used tracers are N2O and
CH4. This reflects their differing lifetimes (which facilitates their use in transport studies), as
well as the fact that they are among the more easily observed source gases. Ideally both
should be observed as their lifetimes in the atmosphere are sufficiently different to provide
complementary information. Both gases also play important roles in the stratosphere in the
catalytic cycle of ozone and, furthermore, of water vapour through the oxidation of
methane. N2O and CH4 are also greenhouse gases.
Carbon Monoxide (CO) - this is an important gas in the budget of tropospheric ozone as
the oxidation of CO in the presence of NOx leads to the production of ozone. In NOx -poor
regions CO oxidation results in the loss of ozone. CO also serves as a tracer for
tropospheric air transferred into the stratosphere, notably associated with deep convective
activity which, above continental regions, often penetrates into the stratosphere.
Carbon Dioxide (CO2) - this is one of the most well-known end product of the burning
(oxidation) of fossil fuels and biomass. Associated with increasing industrial activity, levels
increased dramatically during the last century and are expected to continue to increase well
into the future. CO2 is an important greenhouse gas, having little interaction with solar
radiation but absorbing infrared radiation from the Earth's surface. Increasing CO2 levels
are expected to lead to tropospheric warming, with model predictions of increases over the
next century in the global average surface temperature ranging between one and a few
degrees. The large-scale long term monitoring of CO2 is of critical importance.1
The concentrations of source gases can vary significantly with height in regions where they
photolyse. This means that for observations of these species to be useful they must have a
vertical resolution that is no worse than the scale height (6-8 km). However, in general, a vertical
resolution of at least 2-3 km will be required and an even higher resolution (~1 km) would be very
1
In Table B.2e target values in the troposphere are set to meet the most stringent requirements for trend detection
(currently 0.36 ppm/year and only detectable through surface-based observations). Target values for horizontal
resolution (10 km) are set to allow detection of "hot spots" of CO2 emissions from satellites (total column). Lower
stratospheric CO2 measurements are important for obtaining the seasonal cycle of CO2 which has an amplitude of about
4 ppm in the tropics (transport process studies). Upper stratospheric CO2 measurements reflect only the annual
increase. In addition, height resolved stratospheric CO2 measurements are used for deriving temperature.
16
useful. As spatial and temporal variations are important, high horizontal resolution, coupled with
high precision will be essential.
b)
Reservoir Species (Tables B.3)
The concentrations of reservoir species in the stratosphere will tend to reflect the total
burden of a given class of constituents. Thus, for example, hydrogen chloride (HCl) is a good
indicator of the total chlorine burden in the atmosphere. This means that a high priority for the
measurement of reservoir species lies in absolute accuracy (so that burdens can be compared
with those suggested by summing concentrations of source gases) and long term stability. This is
especially true for measurements of total column amounts and vertical profiles made in regions of
small vertical and horizontal gradients (e.g. hydrogen chloride in the stratopause region).
The highest priority reservoir species for long term measurement are the hydrogen halides
and nitric acid. The former provide the best indication of the total halogen burden in the
stratosphere, which is expected to change with time (and recently indicated in satellite data) as the
surface concentrations of CFCs and related molecules decrease in response to The Montreal
Protocol on Substances that Deplete the Ozone Layer. Nitric acid is the dominant reservoir for
inorganic nitrogen in the stratosphere and is subject to loss from the gas phase through
incorporation into polar stratospheric clouds or aerosols:
Hydrogen Chloride (HCl) - this reservoir species is the “ultimate fate” of chlorine species in
the stratosphere and near the stratopause; essentially all the chlorine is in the form of HCl.
It is important therefore to ensure the long term provision of measurements of the vertical
profile of HCl in the stratosphere to complement the ground-based total column
measurements provided by the NDSC. This is especially true for the stratopause region.
Nitric Acid (HNO3) - this is an important atmospheric trace gas which serves as a reservoir
for reactive nitrogen in both the troposphere and stratosphere. It is highly soluble and can
be absorbed on ice as well as by water, so that its distribution tends to follow a downward
motion in the atmosphere whether associated with precipitation (rapid) or the sedimentation
of hydrometeors (slow). Particularly in the polar stratosphere, this leads to denitrification
which has the consequence of reducing the uptake of reactive chlorine into the chlorine
nitrate reservoir, ultimately enhancing the ability of chlorine to catalyse ozone destruction.
Also in the polar stratosphere, HNO3 is a constituent of Type I polar stratospheric clouds.
c)
Free Radicals (Table B.4)
The concentrations of free radicals vary significantly with tropospheric and stratospheric
conditions as well as with time of day. A key requirement, therefore, is for measurement
techniques to be able to handle very large variations in observed concentrations. Long term
precision is probably of less interest than short term accuracy, as the need is to be able to test
consistency between the observed distributions of radicals and their precursors using atmospheric
models.
The most important free radicals to observe in the stratosphere are chlorine monoxide
(ClO), bromine monoxide (BrO) and at least one (preferably both) of the simple nitrogen oxides
(i.e. nitric oxide – NO; nitrogen dioxide - NO2). The measurement of BrO is especially challenging
given its low concentrations. The need for observations of the hydroxyl radical (OH) depends on
the validation of current hypotheses. If these are confirmed this variable will not need to be
observed directly as it will be possible to derive it from other observations:
Chlorine Monoxide (ClO) - this is one of the free radicals most closely associated with the
destruction of odd oxygen. Its presence indicates on-going ozone destruction via the
reaction Cl+O3→ClO+O2. ClO reacts rapidly and releases Cl, firstly via a reaction with
atomic oxygen forming Cl plus O2, and secondly via a reaction with NO, forming Cl plus
NO2, (this also constitutes an important coupling with the nitrogen cycles).
17
A third rapid process retrieving Cl from ClO is photodissociation. The catalytic cycles
involving Cl and ClO which destroy ozone can be stopped by the (slower) reactions of Cl
with hydrogen compounds, most importantly methane, forming the reservoir species HCl.
Another important channel for removing active chlorine is the reaction of ClO with NO2,
forming the reservoir species ClONO2 (which again can dissociate in the ultraviolet). ClO is
therefore a key species in active stratospheric chlorine chemistry.
Bromine Oxide (BrO) - despite its much smaller abundance in the stratosphere compared
to that of ClO, the presence of BrO, is highly significant for ozone destruction because of
the "per-atom" effectiveness of bromine in destroying ozone. Recent evidence also seems
to suggest that, in addition to its role in the polar stratosphere, the presence of BrO in the
troposphere during the polar spring is important and is highly synergistic with ClO.
The catalytic cycle involves the ozone depleting reaction Br+O3→BrO+O2 and the
‘recycling’ of Br from BrO. This can be effected (similar to the ClO cycle) by reactions with
atomic oxygen or NO, as well as with another BrO molecule. A strong synergy is achieved
if ClO and BrO appear together as they accelerate Br and Cl retrieval through the reaction
BrO+ClO→Br+OClO→Br+Cl+O2.
Nitrogen Dioxide (NO2) and Nitric Oxide (NO) - NO2 (along with its sister species NO) plays
an important role in atmospheric chemistry. In the stratosphere it participates in the
catalytic destruction of ozone, while in the troposphere its presence largely determines the
rate of in-situ photochemical ozone production.
Conversely, the sedimentation of polar stratospheric cloud particles containing nitric
acid may enhance the future loss of ozone by reducing the conversion of ClO to ClONO2.
Further uncertainties are associated with factors such as the production of NOx by
lightning, aircraft emissions and the convective transport of surface level pollutants. This
means that the global budget of reactive nitrogen is both uncertain and variable in time,
especially in the vicinity of the upper troposphere/lower stratosphere. Observations of NO2
and its sister NO are essential to contain this uncertainty.
2.3.3 Meteorological Parameters (Table B.2a and Tables B.5)
To obtain a full understanding of the distribution and concentration of ozone and
associated trace species in both the troposphere and the stratosphere, knowledge of certain
meteorological parameters is essential. Some of these are also required to drive the algorithms
used to retrieve ozone and other variables. The list of relevant meteorological parameters includes
vertical profiles of temperature and water vapour, the height of the tropopause, cloud information
and wind profiles. Wind profiles are needed to take proper account of atmospheric dynamics and
transport mechanisms, especially in the upper troposphere and in the stratosphere, when
interpreting ozone observations.
Most of the requirements for knowledge of meteorological parameters, as defined by the
Upper Air Project in support of IGOS, also encompass the needs of the Ozone Project (in fact
many actually exceed them). Thus, assuming that these requirements are met, here in this report
the focus is on the two notable exceptions, namely tropopause height and levels of water vapour in
the region of the upper troposphere/lower stratosphere. In both instances the requirements of the
Ozone Project are more stringent. The actual requirements for tropopause height are for
knowledge to 0.1 km (target) and 0.2 km (threshold) assuming the WMO definition of tropopause
(based on thermal stability). The detailed requirements for water vapour are listed in Table B.2a
and those for temperature and wind in Tables B.5.
The more exacting requirements associated with tropopause height arise primarily from its
use as an indicator of changes in ozone column amounts. The need to accurately characterise
water vapour levels in the upper troposphere and lower stratosphere (which can be very sensitive
to the temperature of the tropopause) stems from the important role that water plays in controlling
the chemistry, radiative balance and particle formation in this part of the atmosphere. Here
18
concentrations are very small from a meteorological point of view and the requirements defined by
the Upper Air Project do not sufficiently constrain the distribution of water vapour for the use of
these data in chemistry studies.
2.3.4 Aerosol (Tables B.6)
The dominant source of stratospheric aerosol are the major volcanic eruptions that deposit
volcanic ash and aerosol precursor gases (i.e. sulphur dioxide that is rapidly oxidised to sulphuric
acid and nucleated into fine particles) into the stratosphere where it can reside for up to 3 years,
depending on its location above the tropopause. This means that the stratospheric aerosol burden
is essentially determined by volcanic activity.
The properties of stratospheric aerosol, which are relevant to the stratospheric ozone
budget and essential for retrieving ozone concentrations, are the extinction coefficient (Table B.6
b) and (derived from this information) the size distribution and surface area/volume (Table B.6 c)
and aerosol backscatter (Table B.6 d). These properties are measured or inferred from a few
ground-based stations (aerosol lidars) or (occasionally) from aircraft or balloon platforms. The
accuracy and precision levels listed in these tables as "target" are indeed achievable with these
systems and comfortably meet the target requirements stated by the user, in particular for
addressing the issue of ozone destruction on aerosol surfaces and for incorporating the required
aerosol parameters in the ozone retrieval algorithms. Some ozone sensors (limb viewing) cease
operation when optically dense aerosol is present
Since aerosols exhibit very strong vertical (and horizontal) gradients, the vertical resolution
has been set rather tightly allowing, for example, the assessment of the impact of the presence of
aerosols on ozone concentration. In addition, consideration was given to the climate forcing of
stratospheric aerosol which requires not only extinction/backscatter measurements approaching
the stated target values, but also the ability to detect long term trends (~1% per year) in both the
stratospheric aerosol burden and in the total aerosol column. The threshold requirements (of about
20 % per year) are essentially determined by the need to detect the presence of large quantities of
volcanic aerosol after major eruptions.
The requirements to be able to detect the presence of polar stratospheric clouds (PSCs)
responsible for the processes that lead to ozone destruction and ultimately to the annually
recurring ozone hole phenomena, are summarised in Table B.6 a. Because of the relatively high
optical density of PSCs, their detection from space and ground seems to be feasible if the
measurements lie within the limits stated in Table B.6 d.
The importance of tropospheric aerosol is related to a lesser degree to ozone itself, but
more to the measurement of UV-B fluxes at the surface, to aerosol forcing (Earth radiation budget)
and most importantly to air quality issues. Regional haze originating from fossil fuel combustion or
biomass burning and dust storms are but a few of the issues that challenge the science
community. To satisfy their respective needs requires that the target values listed in Tables B.6 bd are closely met, not only with regard to RMS and bias error but also for vertical resolution. At a
minimum, measurements must differentiate between the aerosol residing in the planetary
boundary layer versus that in the free troposphere. Unlike stratospheric aerosol, tropospheric
aerosol is highly inhomogeneous, both in space and time, and, to complicate the situation further,
in chemical composition and physical characteristics.
2.3.5 Spectrally Resolved Solar Ultraviolet Irradiance
Accurate knowledge of levels of solar ultraviolet radiation, which drives atmospheric
photochemistry and provides the photons that ultimately reach the Earth's surface, is essential if
quantitative knowledge of the relationship between atmospheric ozone levels and surface
ultraviolet radiative fluxes is to be obtained. Some information can be obtained based on the use
of proxy quantities for solar variability and observed relationships between spectrally resolved
solar ultraviolet radiation and these proxies. However, the possible variation in the wavelength
19
dependence of solar output over multiple solar cycles indicates that the direct measurement of
solar ultraviolet spectral irradiance must be carried out on a regular basis.
a)
Top of the Atmosphere
For top of the atmosphere (TOA) solar irradiance measurements the key requirement is a
daily measurement of about 30 minutes per day (total and spectral). The wavelength range
coverage needed to link atmospheric photochemistry and surface ultraviolet radiation extends from
approximately 200 to 400 nm (wavelengths shorter than 200 nm are mainly important in controlling
the extent and temperature of the mesosphere and the thermosphere). Wavelengths in the near
infrared up to about 2000 nm are needed for the study of water vapour absorption and cloud
processes. A wavelength resolution of the order of 0.5 nm is required, especially in the UV-B
region, where the absorption cross section of ozone exhibits significant wavelength dependence
which will have a major impact on the surface flux of ultraviolet radiation.
The specific requirements for solar spectral irradiance observations are based on known
cyclical variations and their expected effects on atmospheric chemistry and radiation. For the
wavelength range 200 to 2000 nm, absolute accuracy should be 0.03% with a relative accuracy of
0.01% per year. For shorter wavelengths, absolute accuracy and relative accuracy should be
better than 5% and 1% per year, respectively. Wavelength resolution at shorter wavelengths (but
greater than 200 nm) should be higher (approximately 0.2 nm) but can then be reduced to 30 nm
above 1000 nm.
b)
Surface Measurements
For surface measurements of ultraviolet radiation the requirements are for observations
longer than 290 nm because radiation of shorter wavelengths are filtered out by ozone. For the
rest of the spectrum spectral resolution requirements are similar to those noted above. However,
the required frequency of observation is much greater as there are many short term variations in
surface ultraviolet flux associated with variations in cloud amounts, as well as in aerosol amounts
and the overlying ozone column. There is also a change in solar zenith angle over the course of
the day that affects surface ultraviolet fluxes.
As there can be rapid changes in radiance due to the overhead passage of clouds, it is
important that ultraviolet spectral measurements are made continuously during these periods to
ensure that temporal and wavelength variation are discernable. They must also provide good
spectral discrimination as there is an enormous variation in the surface ultraviolet flux with
wavelength due to the existence of a sharp “cut-off” in ozone absorption in the atmosphere. For
studies of surface ultraviolet radiation under cloudless conditions, ozone profiles (in stratosphere
and troposphere) are needed. Aerosol optical depth are also controlling factors and should be
measured.
20
3.
3.1
AVAILABLE AND PLANNED MEASUREMENTS
Introduction
In this chapter, the sources of observations of ozone, associated meteorological
parameters, other trace constituents and related parameters (discussed in Chapter 2) are
considered within the context of the concerns of the Ozone Project. The emphasis is on ground-,
balloon-, airborne and space-based measurement systems capable of the routine operational
provision of these data. Little attention is given to process-oriented measurements such as those
involving research aircraft or balloons, which typically do not provide data sets relevant to the
study and interpretation of long term global trends which are the concern of this report.
Requirements for some parameters traditionally measured by the operational
meteorological agencies have been identified in this report. The provision of these data is
considered in Chapter 4, The Harmonisation of Provisions and Requirements. The focus is on
instances where the data normally provided operationally by meteorological agencies are not likely
to meet the requirements for long term ozone monitoring (see also Chapter 2).
In addition, it is important to note that some measurements of clear relevance to the long
term monitoring of ozone, most notably surface level ozone measurements, are made through
networks operated by air quality-oriented agencies. The Global Atmosphere Watch (GAW) and its
surface ozone data base can play a critical role in assuring the availability, representativeness and
uniform data quality of such observations. It is important that such measurement networks will
continue to exist and be well maintained.
The information presented in this chapter was obtained from the institutions, agencies, and
programmes responsible for the observing systems described. Much of the material on spacebased measurements was taken from an article “Summary of Space-Based Observations of
Atmospheric Chemistry” which appeared in a newsletter of the Stratospheric Processes and their
Role in Climate (SPARC) subgroup of the World Climate Research Programme (WCRP).
3.2
Non-Satellite Measurements
A wide variety of non-satellite instruments and platforms are available and in operation for
making routine total column and profile ozone measurements. As many of these also make
measurements of other trace constituents, instruments that measure ozone and related
parameters are treated together. Some of these activities are incorporated into national and
international networks such as the NDSC and the WMO GAW, while others make measurements
primarily on a campaign basis. Both types of measurement can make valuable contributions to the
provision of the data required to quantify and interpret changes in the global ozone distribution, as
well as helping to validate the accuracy and precision and hence the stability of satellite
observations.
3.2.1 Ground-based in-situ Measurements
The ground-based in-situ measurements most relevant to the interpretation of ozone
observations concern surface-emitted, long-lived source gases that give rise to chemically active
species (including those containing chlorine and bromine) in the atmosphere, or are radiatively
active in climate forcing. Several well-established, geographically distributed networks exist for
monitoring the long term evolution of the concentration of these species, notably the Advanced
Global Atmospheric Gases Experiment (AGAGE) network of the US National Aeronautics and
Space Administration and the flask sampling network of the US National Oceanic and Atmospheric
Administration. A map of ground-based in-situ sampling stations which have long term data
records of trace constituent composition is shown in Figure 3.1.
21
These networks place substantial emphasis on the high quality, consistent calibration of
instruments' accuracy and precision over the long term. They routinely observe the full range of
chlorofluorocarbons (CFCs) and related halocarbons (methyl chloroform and carbon tetrachloride),
bromine-containing halons and methyl bromide, hydrogenated chlorofluorocarbons (HCFCs) and
other CFC replacement compounds, as well as methane and nitrous oxide. In so doing, they cover
all the source gases listed in Table 1.1 (and Table 1.2) for which the primary requirement is for
regular observations at ground level. It is worth noting that the list of species whose concentrations
are being monitored is slowly expanding to include shorter-lived species such as methyl bromide,
as well as the long-lived species that were the original focus of these networks.
The stations cover a range of geographic locations, including relatively unpolluted areas, so
that the atmospheric “background” is well characterised and contamination from polluted urban air
is minimised. Individual stations operated by scientists in other nations also exist, and the
calibration of the measurement systems used in these has, in many cases, been compared with
that of the AGAGE and NOAA networks. Table 3.1 lists all the trace species/parameters observed
(though not all be every station). It will be noted that some also measure ozone profiles and
column amounts.
3.2.2 Ground-Based Remote Sensing Measurements
Ground-based remote-sensing instruments for atmospheric chemistry measurements can
be viewed as falling into overlapping groups:
•
those that have been designed primarily to make ozone measurements versus those
that have been developed to provide a more comprehensive set of atmospheric
observations
•
those designed primarily for the measurement of total column amounts versus those
designed primarily for the measurement of vertical distributions (this breakdown is not
completely clean - for example the ultraviolet-visible and the Fourier transform infrared
instruments (see below), which have been designed primarily to measure column
amounts, also provide some information on the vertical distributions of a few
constituents, notably NO2 and CO, respectively).
As indicated above, Table 3.1 lists the species (plus aerosols and UV flux) measured by
the different ground-based remote sensing systems, including those for which profile and column
amount information are available (and the source of these data). Table 3.2 summarises the
instrumentation available in the NDSC, including both the primary (that contain the full range of
NDSC instrumentation) and complimentary sites. A map showing sites currently affiliated to the
NDSC is reproduced in Figure 3.2. Particular issues related to calibration, validation, and data
management for these systems are discussed in Chapter 5.
22
23
Table 3.1: The list of species observed by ground-based observing stations
and (where appropriate) the technique used to observe vertical profiles or column
amounts
INSTRUMENT TYPE
SPECIES
LIDAR
FTIR
UV/VIS
µWAVE
Sondes
O3
p
p
c
p
p
N2O
c
NO
c
NO2
c
NO3
Dobson
/Brewer
p
UV
Spectrometer
p
p
p
c
HNO3
p
p
HNO4
N2O5
CFCl3
c
CF2Cl2
c
CF3CCl3
CCl4
c
CH3CCl3
CH3Cl
c
HCl
p
ClO
p
OclO
p
ClONO2
c
HF
c
CF2O
c
CF3Br
CF2ClBr
CH3Br
BrO
p
H2O
p
p
H2O2
p
p
OH
c
HO2
p
CH4
p
CO
p
SF6
c
CF4
c
OCS
c
p
SO2
HCN
c
T
p
p
Aerosols
p
p
UV Flux
p
Note: "p" - profiles and column amounts
"c" - column amounts only
24
Table 3.2 (a): Instrumentation at NDSC primary sites - at some stations instruments may only be operational during campaigns.
(Notes - "O3 (A)" indicates ozone lidar with aerosol channel; "O3(T)" indicates ozone lidar for troposphere (below 15 km) only;
"A" indicates aerosol)
STATION NAME
COUNTRY
LAT.
LONG.
ELEV.
(M.)
LIDAR
FTIR
UV/VIS
µWAVE
SONDES
DOBSON/B
REWER
O3
B
O3
D
SPEC. UV
Arctic
Eureka
Canada
80.05
-86.42
610
O3 , A
X
Ny Alesund
Norway
78.92
11.93
15
O3, A
X
X
Thule
Greenland
76.53
-68.74
30 to 220
A
X
X
Sondre Stomfjord
Greenland
67.02
-50.72
180 to 300
Garmisch
Germany
47.48
11.06
734
Zugspitze
Germany
47.42
10.98
2964
Bern
Switzerland
46.95
7.45
550
Jungfraujoch
Switzerland
46.5
8
3580
Observ. de Bordeaux
France
44.83
-0.52
73
Plateau de Bure
France
44.63
5.9
2550
Obs. Haute Provence
France
43.94
5.71
650
Mauna Kea
USA
19.83
-155.48
4204
Hilo
USA
19.72
-155.58
11
Mauna Loa
USA
19.54
-155.58
3397
O3, A, O3(T)
X
X
O3, H2O
O3
D
X
Lauder
New Zealand
-45.05
169.68
370
O3 , A
X
X
O3, H2O
O3, A
D
X
Dumont d'Urville
Antarctica
-66.67
140.01
20
O3 , A
Arrival Heights
Antarctica
-77.82
166.68
O3, ClO,
H2O
O3
Term 96
B
Alpine
A, O3(T)
X
X
X
O3
X
X
ClO
O3, H2O
ClO
X
O3, H2O, A,
O3(A)
O3
D
Hawaii
ClO
O3
Antarctic
McMurdo
Antarctica
-77.80
166.68
Scott Base
Antarctica
-77.85
166.78
South Pole Station
Antarctica
-90
N/A
X
X
10
A
O3
X
Term 94
O3, A
ClO
O3
25
D
Table 3.2 (b): Instrumentation at NDSC Complimentary Sites - at some stations instruments may only be operational during
campaigns. (Notes - "O3(A)" indicates ozone lidar with aerosol channel; "O3(T)" indicates ozone lidar for troposphere
(below 15 km) only; "A" indicates aerosol)
STATION NAME
COUNTRY
LAT.
LONG.
ELEV.
(M.)
LIDAR
FTIR
A, O3
X
UV/VIS
Scoresbysund
Greenland
70.48
-21.97
Andoya
Norway
69.3
16
Kiruna
Sweden
67.83
20.42
X
Sodankyla
Finland
67.37
26.63
X
Zhigansk
Russia
67.2
123.4
X
Norway
60.2
10.8
Zvenigorod
Russia
55.4
36.5
A, O3
Aberystwyth
UK
52
4
A, O3
Japan
44.4
142.3
Toronto
Canada
43.8
-79.5
SONDES
X
Harestua
Moshiri
µWAVE
560
X
O3
X
X
X
X
X
X
X
X
O3
A,O3
Rikubetsu
Japan
43.5
143.8
Greenbelt
USA
38.9
-76.7
370
Wallops Island
USA
37.93
-75.48
Mt. Barcroft
USA
37.6
-118.2
Billings (OK)
USA
36.61
-97.48
Tsukuba
Japan
36.05
140.13
Kiso
Japan
35.8
137.6
Table Mountain (CA)
USA
34.4
-117.7
2300
Kitt Peak
USA
32
-111.5
2120
Tarawa
Kiribati Rep.
1.4
172.9
X
Bandung
Indonesia
-6.4
107.4
X
A
O3
X
315
X
O3
X
O3, O3(T), A
H2O
X
26
DOBSON
SPEC. UV
Table 3.2 (c): Instrumentation at NDSC Complimentary Sites (continued) - at some stations instruments may only be
operational during campaigns. (Notes - "O3(A)" indicates ozone lidar with aerosol channel; "O3(T)" indicates ozone lidar for
troposphere (below 15 km) only; "A" indicates aerosol)
STATION NAME
COUNTRY
Reunion Island
LAT.
LONG.
-21.8
55.5
ELEV.
LIDAR
A
FTIR
UV/VIS
X
Durban
South Africa
-34.4
???
Wollongong
Australia
-34.4
150.9
Campbell Island
New Zealand
-53.4
169
Term 95
-54.5
158.95
X
Term 95
Macquarie Island
X
Faraday
Antarctica
-65.25
-64.27
Rothera
Antarctica
-67.57
-68.12
X
Syowa Base
Antarctica
-69.01
38.59
X
SA Antarctic Station
Antarctica
-70
-2
X
Halley Bay
Antarctica
-75.58
-26.77
X
27
µWAVE
SONDES
O3
DOBSON
SPEC. UV
Figure 3.2: Map of primary and complementary sites affiliated to the NDSC
28
a)
Column Measurements
The Dobson Spectrophotometer has a history of high quality total ozone observations
stretching back nearly 70 years and regular measurements have been made with it for
about 40 years. The current WMO-GAW network includes approximately 70 stations with
many of these concentrated at mid-latitudes in the northern hemisphere (e.g.33 in Europe).
Almost all of these instruments have their calibration tied to a single standard Dobson
instrument (#83) through regional and national standard Dobson instruments. Although the
continuation of this network has often been clouded by uncertainty, the on-going efforts of
the WMO-GAW programme and the importance of the long term data set based on this
network, have allowed it to survive basically intact. A map showing the regularly reporting
Dobson and Brewer Spectrometer stations, as well as those using other well-established
techniques (such as filter instruments) to measure total column ozone is shown in Figure
3.3. Annex C provides further information on the data records available from regularly
reporting ground-based ozone measuring stations.
The Brewer Spectrometer is a high quality instrument which measures ozone, as well as
several other constituents, by making spectral measurements in the UV-B part of the solar
spectrum. Its high performance coupled with the feasibility of automating its operation, has
led to the deployment of about 70 of these instruments in the network. As with the Dobson
instrument, many are concentrated at mid-latitudes in the northern hemisphere (e.g. 20 in
the U.S.). A reference triad of Brewer instruments is maintained at MSC Canada as a
standard and, at least initially, the station instruments are linked to this standard. The
Brewer is also a component of the GAW network and about 15 of them are included within
the NDSC. There are also travelling standards.
The Ultraviolet-Visible Spectrometer, of which the SAOZ is the most widely used
example, is able to obtain total ozone amounts at low sun elevation angles when
instruments such as the Brewer and Dobson are not capable of making measurements.
This has led to them being mainly sited at the poles for use in polar winter conditions
though they are also used in other latitudes. The calibration of these instruments is not as
well established as is the case for the other two instruments but work within the NDSC
should help remedy this situation. These instruments can also be used to measure other
trace constituents with strong absorption in the visible and ultraviolet wavelength regions
such as NO2, NO3, BrO and OClO.
Fourier Transform Infrared Spectrometers (FTIR) can be used to make measurements
of a whole host of atmospheric constituents in addition to ozone, including a number of
long life gases (methane, nitrous oxide, water vapour, carbon monoxide and selected
CFCs) and important reservoir molecules like hydrogen chloride, hydrogen fluoride, nitric
acid and chlorine nitrate. Column amounts of such species measured over many years
using FTIRs have been critical in documenting the increasing concentrations of
halogenated species in the atmosphere. The nearly two dozen FTIR instruments affiliated
with the NDSC are operating according to protocol rules established and up-dated by an
ad-hoc NDSC working group. A mobile FTIR serves as a "reference" to ensure internal
consistency for this type of instrumentation throughout the network. Furthermore, a strong
effort is underway within the NDSC and WMO-GAW stations to ensure the provision of
high quality measurements and, even now, FTIR ozone amounts are routinely compared
with Dobson and Brewer observations.
29
30
Filter Instruments have had a complex history due to problems with filter stability which limits
the ability of such instruments to make accurate long term measurements. A network of 40 filter
instruments, mostly in the Russian Federation, report data. Recent advances in the ability to make more
stable filters leaves open the possibility that such instruments may, ultimately, be able to make important
contributions to long term records of ozone column amounts (also aerosols). A notable example of such
efforts is the Atmospheric Radiation Measurement (ARM) programme under the auspices of the US
Department of Energy. Other filter instruments are also used extensively for the measurement of
surface fluxes of ultraviolet radiation. Their long term stability remains to be proven, although preliminary
indications suggest that it is much improved over that of its predecessors. Unless these filters have a
fairly narrow spectral band pass (e.g.1-2 nm) there are additional complications associated with their
use for ultraviolet trend measurements.
b)
Profile Measurements
Dobson and Brewer instruments are both capable of exploiting the Umkehr technique to
produce vertical profiles of ozone in the stratosphere. These profiles have an altitude resolution
of 5 km or greater but suffer from the same geographical distribution constraints as the total
ozone observations made with these instruments. Only a limited number of the Dobson locations
(15) make profile observations and most of these are where the Dobson instrument has been
automated. The Brewer is, by its very nature, an automated instrument so that its potential for
profile observations is much greater than is the case with the Dobson, but at present only a
limited number of profiles are being reported.
Lidars are used to obtain profiles of atmospheric variables in both the stratosphere and
troposphere with one to two kilometer resolution. In the stratosphere they are used to measure
profiles of ozone and temperature at over 15 locations world wide. Most of these instruments are
affiliated with the NDSC as primary or complementary sites. The NDSC has carried out several
validation campaigns and concluded that these instruments produce valid data in the range of
15-50 km for ozone and up to 80 km for temperature. In addition, a few tropospheric versions of
these instruments are currently operating, mostly in a campaign mode, though nine are
committed to long term operation as part of existing international networks including the NDSC.
They are used primarily to measure tropospheric ozone profiles and, at some stations, water
vapour profiles in the upper troposphere. Lidars also make important contributions to the long
term observation of stratospheric aerosols. An international lidar network has been developed
which provides very extensive spatial coverage, although as with all ground-based instruments,
measurements are restricted to land-covered areas. Observations from developing countries and
remote territories are much fewer than from more populated, developed areas.
Microwave Radiometers are used to observe ozone profiles from the stratosphere up to the
mesosphere and are able to make measurements under most weather conditions. They are
currently being operated at several NDSC sites. The validity of their ozone profiles has been
established through validation campaigns and by intercomparison with other profile
measurements. As they observe in emission, these instruments can make measurements during
both day and night (including the polar night). Microwave observations of diurnal variations and at
the South Pole have been particularly important as such instruments can also be used to make
measurements of a range of trace constituents, the most important of which are H2O and ClO, as
well as long-lived molecules like N2O. The vertical resolution of these instruments is typically fairly
broad (5-10 kilometers) which places constraints on the usefulness of their data in regions of
strong vertical gradients.
FTIR and UV/Visible Instruments can provide profile information on some gases although their
primary use has been for determination of total column amounts. FTIR instruments make use of
the pressure variation of the line width (and the temperature dependence of thermal emission)
and have been shown to provide low vertical resolution information on species such as CO, CH4,
HCl, HNO3, O3 and H2O,. UV/Visible instruments can make profile measurements at twilight
when the Earth’s shadow line is scanning upwards in altitude. Such measurements have been
made for NO2, OClO, and BrO.
31
c)
Balloon-Based Measurements
For many years now balloon-borne instruments have been used to make the long term global
observations of ozone required to monitor ozone trends (with the main focus in the past on the
stratosphere). For this ozone sondes have been utilised and, at present, these sondes provide the bulk
of the data on vertical profiles of ozone from near the surface to approximately 30 km. The observations
derived from ozone sondes are of a very high vertical resolution which is unattainable by any of the
existing (or near-term projected) satellite techniques.
Regular soundings are currently made at about 40 sites. Although these tend to be concentrated
at middle and high latitudes in the northern hemisphere, several of the more recently established sites
are in the under-sampled tropical and subtropical regions. About half of the sites have records that
extend 10 years or longer and most stations are affiliated with the WMO/GAW network; some to the
NDSC. A map of regularly reporting ozone sonde stations is shown in Figure 3.4. Information on the
available data from the different sonde stations (e.g. length of record, frequency of flights) is included in
Table 3.3. An effort has recently been made to increase the frequency of ozone sonde launches in the
tropics and southern hemisphere subtropics through the Southern Hemisphere Additional Ozone sonde
(NASA/SHADOZ) programme.
Long term information on stratospheric composition may be obtained through the judicious use of
the results of long series of process-oriented balloon profiles (correcting for seasonal and geographic
differences between flights). This has been achieved by relating concentrations of the more rapidly
changing species (like the CFCs) to those of more slowly changing ones (like nitrous oxide) which can
help establish a reference co-ordinate system for the measurements. Measurement validation has been
through field intercomparison campaigns and most recently through the use of the simulation facility at
the Research Centre in Jülich, Germany (WMO-GAW world calibration facility for ozone sondes).
In addition, there are several programmes where ozone and other trace constituents are
measured as part of a larger process-oriented balloon payload. These measurements are particularly
useful as they are made with instruments capable of observing a complement of photochemical and
tracer species in addition to ozone. Campaigns take place on a regular basis within the US and
European (notably the French and German but see Table 3.4) balloon programmes. They include large
payloads such as the Observations of the Middle Stratosphere (OMS) programme, as well as flights of
payloads like the SAOZ, AMON and MIPAS instruments. The long duration Montgolfier balloon could be
very promising and is planned to be flown in the next few years. Balloon flights also provide an important
element of satellite calibration and validation programmes (e.g., UARS, ADEOS, and for the SAGE III
and ENVISAT campaigns).
d)
Airborne Measurement Programmes
The only currently operational programmes in which atmospheric trace constituents are routinely
measured on board aircraft are the European MOZAIC and CARIBIC programmes, in which in-situ
ozone photometers, water vapour and NOy measuring instruments have been placed on French and
German airliners. These fly international routes between Europe and Asia, North and South America,
and Africa, with the heaviest concentration of flights over the North Atlantic. The sampling is primarily in
the upper troposphere but does include some stratospheric data. Profile information can be obtained
during take off and landing. The MOZAIC programme dates back to 1993 and was preceded by the
NASA/GASP in the seventies which may be viewed as the precursor to MOZAIC. In addition, an
instrument suite is currently under development in the US for the routine measurement of ozone, water
vapour, carbon dioxide and tetrachloroethylene. The long term goal of this activity is operational use on
commercial aircraft, supplementing the MOZAIC and CARIBIC programmes.
32
33
Table 3.3: The WMO-GAW data records of regularly reporting ozone sonde stations
(note that some of these have operated only over limited time intervals and so their
data are not suitable for trend calculations)
STATION LOCATION
COUNTRY
LAT.
LONG.
START
Alert
Eureka
Ny Alesund
Resolute
Canada
Canada
Norway
Canada
82.5
80.05
78.89
74.72
-62.3
-86.42
11.88
-94.98
Sodankyla
Yakutsk
Churchill
Finland
Russia
Canada
67.4
62.08
58.75
26.6
129.75
-94.97
Edmonton
Canada
53.55
-114.1
Legionowo
Lindenberg
Poland
Germany
52.4
52.21
20.87
14.12
de Bilt
Uccle
Netherlands
Belgium
52.06
50.8
5.00
4.35
Prague
Czech Rep.
50.02
14.45
Hohenpeissenberg
Payerne
Haute Provence
Sapporo
Boulder
Wallops Island
Tsukuba/Tateno
Kagoshima
New Delhi
Izana (Tenerife)
Naha
Taipei
Hong Kong
Hilo
Petaling Jaya
Kodaikanal
Nairobi
Natal
Watukosek
Ascension Island
Samoa
Reunion Island
Pretoria/Irene
Easter Island
Melbourne/Aspendale
Lauder
Marambio
Syowa
McMurdo\Aug-Oct
Neumeyer
Amundsen-Scott
Germany
Switzerland
France
Japan
USA
USA
Japan
Japan
India
Spain
Japan
Rep. of China
China
USA
Malaysia
India
Kenya
Brazil
Indonesia
UK
USA
France
South Africa
Chile
Australia
New Zealand
Antarctica
Antarctica
Antarctica
Antarctica
Antarctica
47.8
46.82
43.93
43.05
40.03
37.93
36.05
31.55
28.65
28.29
26.2
25.03
22.2
19.72
3.1
10.23
-1.27
-5.84
-7.5
-7.58
-14.25
-21
-25.73
-27.1
-37.8
-45.03
-64.63
-69
-77.83
-79.65
-90
11.02
6.95
5.7
141.33
-105.25
-75.48
140.1
130.55
77.22
-16.49
130.55
121.53
114.3
-155.07
101.65
77.47
36.8
-35.21
112.6
-14.24
-170.56
55
28.18
-109.3
144.97
169.68
-56.72
39.58
166.67
-8.25
N/A
5-Jan-87
1-Nov-82
31-Oct-90
1-May-78
5-Jan-66
1-Jan-89
1-Jan-94
24-May-78
19-Oct-73
17-May-78
1-Oct-70
17-Jan-79
1-Mar-92
14-Sep-74
1-Jan-93
1-Jan-97
9-Nov-66
3-Jan-92
30-Jan-79
8-Mar-65
1-Nov-66
2-Sep-90
5-Dec-68
12-Mar-79
1-Jul-67
6-Mar-68
12-May-68
1-Nov-83
1-Nov-68
12-May-68
1-Jan-92
4-Mar-93
25-Sep-82
1-Jan-92
19-Jul-71
1-Jan-96
10-Aug-79
1-May-93
28-Jul-90
1-Aug-86
1-Sep-92
1-Jul-90
1-Jan-94
1-Jun-65
1-Aug-86
24-Mar-66
17-Mar-66
1-Jan-88
22-Mar-92
1-Jan-86
34
END
30-Nov-79
10-Sep-79
21-Aug-79
29-Feb-92
31-Dec-97
29-Mar-91
SONDE TYPE
ECC
ECC
ECC
ECC
BM
ECC
ECC
ECC
BM
ECC
BM
BM
ECC
OSE
ECC
ECC
BM
ECC
OSE
BM
BM
ECC
Japan
ECC
ECC
Japan
Japan
India
ECC
Japan
ECC
ECC
ECC
ECC
India
ECC
ECC
Japan
ECC
ECC
ECC
ECC
ECC
BM
ECC
ECC
Japan
ECC
ECC
ECC
Table 3.4: Some European balloon-borne experiments
INSTRUMENT
COUNTRY
TECHNIQUE
OTHER SPECIES
AMON
BOCCAD
DOAS
France
France
Germany
stellar occult., UV-VIS spectrometer
solar occult. and scattering, 4-l radiometer
limb viewing, UV-VIS spectrometer
NO2, NO3, OClO, OBrO, aerosol extinction
aerosols
NOx, NOy, BrO, OclO
LPMA
MIPAS
France
Germany
solar occult., FTIR spectrometer
emission, FTIR spectrometer
N2O, NO, NO2, HNO3, ClONO2, HCl, HF, H2O, CH4
N2O, NO, NO2, HNO3, N2O5, ClONO2, H2O, CH4
O3 Semi Conductor
UK
in-situ, solid state sensor
SALOMON
France
moon occult., UV-VIS spectrometer
NO2, NO3, OClO, OBrO, aerosol extinction
SAOZ
France
sun occult., UV-VIS spectrometer
NO2, aerosol extinction
SPIRALE
France
in-situ, IR laser diode absorption spectrometer
NO, NO2, CO, CH4
ASTRID
Germany
in-situ, grab sampler
N2O, CFC-11, CH4
BALLAD
France
limb viewing, VIS-NIR 3-l radiometer
aerosols
BROCOLI
Germany
resonance fluorescence
ClO, BrO
DESCARTES
UK
in-situ, cryogenic air sampler
CFC-11, CFC-113
ELHYSA
France
in-situ,
H2O
FISH
Germany
in-situ, Lyman-alpha hygrometer
H2O
Filter Radiometer
Germany
in-situ, narrow-band UV radiometer
photolysis rate of O3, NO2
Grab sampling
Germany
in-situ, air collection
N2O, CFC-11, CFC-12, CFC-113
LMD-Aerosol
France
in-situ, particle counter
aerosol number
Mass Spec
Germany
in-situ, mass spectrometer
HNO3, H2SO4, HCl, HF
MACSIMS
France
in-situ, mass spectrometer
HNO3, N2O5
RADIBAL,
µRADIBAL
SDLA-LAMA
France
solar scattering, NIR 2-l photopolarimeter
aerosol model and extinction
France
in-situ, NIR laser diode absorption spectrometer
H2O, CH4
Ozone sensors
Other sensors
Research aircraft can carry comprehensive payloads for the study of the chemistry of the
troposphere and stratosphere. Several aircraft/payload combinations exist and have been used
extensively to investigate the stratosphere and upper troposphere. These aircraft programmes
have made enormous contributions to the validation of satellite sensors and to our understanding
of the chemistry of the stratosphere and upper troposphere, as well as of the relationship between
chemical and transport processes. In some cases, the duration and spatial coverage of the
sequence of missions is long enough to be relevant to studies of long term trend issues that are
the focus of this report. Some examples of airborne research campaigns are provided in Annex D.
3.3
Satellite Measurements
In this section, space-based systems capable of providing routine operational observations
of the required parameters (see Chapter 2) are discussed and a summary of their capabilities
presented. The space-based measurement systems are organised into two groups, namely those
that are designed primarily for long term continuous operations and those that are planned as
“one-time” experimental missions. Generally, the lifetimes of the latter are too short for their data
to be relevant to the long term data requirements considered in this report. However, these groups
are to a certain extent complementary and not necessarily exclusive, as some research-oriented
satellites may operate for a sufficiently long time (e.g. UARS now has more than eight years of
operation) that relatively long term studies can be carried out with their data.
35
Within the class of measurements designed for long term operation, presently-operating
and future measuring systems are treated separately. Time lines for space-based measurement
programmes contributing to the study of ozone are shown in Figure 3.5, while Table 3.5 shows the
measurement objectives of the different space-based measurement programmes. In addition to the
instruments and missions listed below, there are many others that provide information of relevance
(e.g. insights into relevant processes) to the Ozone Project. These are listed in Annex E.
3.3.1 Currently Operating Operational Systems
In this section five currently operating measurement systems, designed for the long term
measurement of stratospheric ozone and related parameters, are considered. Additional long term
measurement systems not yet in operation but planned are treated in Section 3.3.2, while relevant
research satellite systems (both present and future) are considered in Section 3.3.3.
a) The Stratosphere Aerosol and Gas Experiment (SAGE II) series of instruments
observe the absorption of visible and near-infrared radiation during solar occultation to
determine the concentrations of ozone, water vapour, nitrogen dioxide, and aerosol
extinction in the stratosphere and, for some parameters, in the upper (cloud free)
troposphere. This technique is self-calibrating and can provide excellent accuracy/precision
and vertical resolution (~1 km), although it has the usual spatial limitations associated with
the solar occultation technique (i.e. two latitudes of observation per orbit corresponding to
local sunrise and local sunset).
The currently operating SAGE II instrument was launched in October 1984 onboard
the Earth Radiation Budget Satellite (ERBS). The previous SAGE instrument (which could
not be used to observe water vapour) operated from 1979-1981. In both instances the
satellites flew in inclined (~57 degree) orbits so their observations cover much of the
Earth’s surface (subject to the usual spatial sampling problems).
A related instrument, the Stratospheric Aerosol Monitor (SAM II) made observations
of PSCs from the Nimbus 7 satellite (1979-1994) using a single near-infrared wavelength.
This satellite flew in a polar-orbiting, sun-synchronous orbit so all the occultations were at
high latitudes, which facilitated its for PSC studies.
b) The Total Ozone Mapping Spectrometer (TOMS) series of instruments makes
measurements of the total column amount of ozone using six ultraviolet wavelengths and
the backscatter ultraviolet (BUV) technique. By exploiting cross-track scanning, the TOMS
instruments typically obtain full daily coverage of the sunlit Earth. The horizontal resolution
2
is typically 50x50 km at nadir. Four TOMS instruments have flown - Nimbus 7 TOMS
(1979-1993), Meteor-3 TOMS (1991-1994), Earth Probe TOMS (1996 - present) and
ADEOS TOMS (1996-1997). An additional TOMS instrument is planned for 2000 on board
the QuikTOMS spacecraft.
With the exception of Meteor-3 TOMS, all the TOMS instruments have flown on
board polar-orbiting, sun-synchronous satellites. Provided the equator crossing times are
close to noon, solar zenith angles will be low and the orbit will be well tuned to the
requirements of TOMS as atmospheric path lengths will be short. In addition to its
measurements of total ozone, it has been shown that TOMS can provide information about
tropospheric aerosols, stratospheric sulphur dioxide (when levels are high due to large
volcanic eruptions), the surface flux of ultraviolet radiation, the ultraviolet reflectivity of the
atmosphere (including the ground and clouds), and (this requires other data and depends
on various assumptions) tropospheric ozone, especially at low latitudes.
36
Table 3.5 (a): Measurement objectives of the different space-based system (note that limb and occultation
instruments measure predominantly stratospheric column not TOTAL column)
Instrument
Platform
Ozone
Column
Ozone
Profile
Aerosol
Column
TOMS
OMI
Aerosol
Profile
Earth Probe
EOS-Aura
X
X
X
X
X
OMPS
NPOESS
X
X
X
SBUV
Nimbus 7
X
X
SBUV/2
X
X
SSBUV
NOAA-11,
14, (POES)
Shuttle
X
X
GOME
ERS-2
X
X
X
SCIAMACHY
ENVISAT
X
X
X
GOME-2
METOP
X
X
X
SAGE I
SAGE II
SAGE III
X
X
X
X
X
X
X
X
X
X
X
X
UVISI
ACE
AEM-2
ERBS
METEOR,
1
ISS & TBD
MSX
SCISAT-1
X
X
X
X
X
X
SMILES
ISS
X
X
IMG
ADEOS
X
X
Constit.
Column
Constit.
Profile
SO2
SO2, BrO, NO2,
CH2O
SO2, BrO, CH2O,
OclO
SO2,
NO (p< 1 mb)
SO2,
NO (p< 1 mb)
SO2,
NO (p< 1 mb)
SO2, BrO, NO2,
CH2O, OClO,
H2O
SO2, BrO, NO2,
CH2O, CO, CH4,
OclO, H2O, N2O
SO2, BrO, NO2,
CH2O, OClO,
H2O
NO2
NO2
NO2, H2O
NO2, H2O
NO2, H2O, NO3, NO2, H2O, NO3,
OclO
OclO
O3, NO2
O3, NO2
About 30
About 30
species
species
ClO, H2O, H2O2, ClO, H2O, H2O2,
HCl, HNO3, BrO, HCl, HNO3, BrO,
H2O, CH4, CO
H2O, CH4, CO
1)
(Note : TBD - to be determined)
37
Temp.
Profile
Winds
Irrad.
Surface
UV
UV/Vis
X
UV/Vis
/NIR
UV
X
UV
UV
UV/Vis
X
UV/Vis
/NIR
X
UV/Vis
X
X
X
X
X
X
Table 3.5 (b): Measurement objectives of the different space-based systems (note that limb and occultation instruments
measure predominantly stratospheric column not TOTAL column)
Instrument
Platform
Ozone
Column
Ozone
Profile
Aerosol
Column
Aerosol
Profile
ODUS
GCOM-A1
X
SOFIS
GCOM-1
X
X
X
X
POAM II
POAM III
SPOT-3
SPOT-4
X
X
X
X
X
X
X
X
LIMS
SAMS
Nimbus 7
Nimbus 7
X
X
SOLSE/LORE
ATMOS
MAS
CRISTA
MAHRSI
Shuttle
Shuttle
Shuttle
Shuttle/SPAS
Shuttle/SPAS
X
X
X
X
X
X
X
CLAES
ISAMS
UARS
UARS
X
X
X
X
X
X
X
X
HALOE
UARS
X
X
X
X
MLS
HRDI
SOLSTICE
SUSIM
UARS
UARS
UARS
UARS
X
X
X
Constit.
Column
Constit.
Profile
Temp. Winds
Profile
SO2, BrO, NO2, CH2O,
OClO
NO2, CH4, CFCl3,
NO2, CH4, CFCl3,
CF2Cl2, HNO3, ClONO2, CF2Cl2, HNO3, ClONO2,
CO2
CO2
NO2
NO2, H2O
NO2
NO2, H2O
NO2, H2O, HNO3
CH4, N2O
NO2, H2O, HNO3
CH4, N2O
Irrad.
Surface
UV
UV/Vis
X
X
X
X
Close to 30 species
ClO, H2O
More than 20 species
OH, NO
Close to 30 species
ClO, H2O
More than 20 species
OH, NO
x
X
x
More than 10 species
H2O, CH4, NO, NO2,
N2O, N2O5,HNO3, CO
H2O, CH4, NO, NO2,
HCl, HF
ClO, H2O, HNO3
More than 10 species
H2O, CH4, NO, NO2,
N2O, N2O5,HNO3, CO
H2O, CH4, NO, NO2,
HCl, HF
ClO, H2O, HNO3
X
X
X
X
X
UV
UV
38
Table 3.5 (c): Measurement objectives of the different space-based systems (note that limb and occultation instruments
measure predominantly stratospheric column not TOTAL column)
Instrument
Platform
Ozone
Column
Ozone
Profile
Aerosol
Column
Aerosol
Profile
Constit.
Column
Constit.
Profile
Temp.
Profile
ILAS
ADEOS
X
X
X
X
NO2, CH4, CFCl3,
CF2Cl2, HNO3
NO2, CH4, CFCl3,
CF2Cl2, HNO3
X
RIS
ADEOS
Osiris
Odin
X
X
X
X
SMR
Odin
X
X
NO2 SO2, CH2O,
NO2 SO2, CH2O,
BrO, OclO, H2O, NO BrO, OClO, H2O, NO
More than 10 species More than 10 species
GOMOS
MIPAS
ENVISAT
ENVISAT
X
X
X
X
x
X
x
X
NO2, NO3, H2O
NO2, NO3, H2O
More than 20 species More than 20 species
ILAS-2
ADEOS-2
X
X
X
X
HIRDLS
EOS-Aura
X
X
MLS
EOS-Aura
X
X
TES
EOS-Aura
X
X
ACE
SMILES
SCISAT-1
ISS
X
X
X
X
X
X
NO2, CH4, CFCl3,
CF2Cl2, HNO3,
ClONO2
NO2, CH4, CFCl3,
CF2Cl2, HNO3,
ClONO2
CFC11, CFC12,
ClONO2, H2O, N2O,
NO2, N2O5, HNO3,
CH4
ClO, H2O, N2O, CO,
SO2
About 30 species
CFC11, CFC12,
ClONO2, H2O, N2O,
NO2, N2O5, HNO3,
CH4
ClO, H2O, N2O, CO,
SO2
About 30 species
About 30 species
About 30 species
ClO, H2O, H2O2, HCl, ClO, H2O, H2O2, HCl,
HNO3, BrO,
HNO3, BrO,
39
X
X
X
X
X
X
X
Winds
Irrad.
Surface
UV
40
c) The Solar Backscatter Ultraviolet (SBUV) series of instruments measures both total
ozone amounts and the vertical distributions of ozone using the backscatter ultraviolet
(BUV) technique. The SBUV instrument also measures spectrally-resolved solar irradiance
from 180 to 405 nm with 1 nm resolution. Instruments in this series have included the
original SBUV instrument which flew on-board the Nimbus 7 satellite and the SBUV/2
instruments which have flown aboard several meteorological satellites (afternoon equatorial
crossing time) operated by the US National Oceanic and Atmospheric Administration
(NOAA), including NOAA-9, NOAA-11, and NOAA-14.
Unlike TOMS, the SBUV instruments are not capable of cross-track scanning, as
they only view in nadir. Vertical profiling is 7 km in the middle and upper stratosphere, with
little sensitivity in the lower stratosphere. The equatorial crossing time of the NOAA POES
spacecraft have drifted which may limit the usefulness of some of these data for high
accuracy trend studies (though this has been taken into account in characterising the data
and the algorithm; future POES platforms will have stable orbits beginning in 2000). Like
TOMS, SBUV can provide some information on sulphur dioxide levels when these are
elevated following volcanic eruption. When operated in a spectral scanning mode it can
also provide information on the column amounts of nitric oxide in the mesosphere and
thermosphere.
Help in calibrating the SBUV instruments during the 1989-1996 period was provided
by observations made by a Shuttle-borne version of the instrument (SSBUV), which made
eight flights over this time period. The SSBUV flights provided a first order correction to the
long term observations of the SBUV/2 series. The SSBUV observations were particularly
important for calibrating the SBUV/2 solar irradiance measurements which correlated well
with the UARS solar irradiance instruments.
d) The Global Ozone Monitoring Experiment (GOME) instrument was launched on
board the European Space Agency’s Earth Remote Sensing satellite (ERS-2) in 1995.
GOME uses a nadir-viewing geometry to measure total column amounts and vertical
profiles of ozone and total column amounts of a wide range of trace constituents, including
BrO, NO2, H2O, SO2, CH2O, and OClO (in the polar vortex), as well as providing
information on clouds, aerosols and surface spectral reflectance (see Table 3.5). The ERS2 spacecraft flies in a polar sun-synchronous orbit which is well suited for such
measurements.
The instrument has a broad spectral coverage (240 - 790 nm) which is coupled with
an excellent spectral resolution (0.2-0.4 nm). This enables it to exploit a combination of
spectroscopic fitting and the backscatter ultraviolet (BUV) technique. Its horizontal
2
2
resolution can vary between 40x80 km and 40x320 km ; on most days it operates at the
latter spatial resolution.
The resolution of GOME ozone vertical profiles is 7-10 km and, because of its multispectral capability, profile information can be derived in both the lower stratosphere and the
upper troposphere unlike BUV measurements. Like SBUV it has been calibrated against
the SSBUV as well as against other instruments (see Chapter 5, Calibration and
Validation). The GOME has a multi-faceted calibration programme including views of the
Sun and the Moon as well as an internal lamp.
e) The Tiros-N Operational Vertical Sounder (TOVS) series of instruments flying aboard
NOAA’s operational meteorological satellites were designed primarily as a source of
meteorological data (notably temperature and moisture). However, in addition, they do
provide information on total column ozone amounts (see also SEVIRI). This measurement
is made using the 9.6 µm channel of the High Resolution Infrared Sounder (HIRS) which
forms part of the TOVS and which was originally included to remove ozone effects from the
temperature sounding channels.
41
There is some uncertainty as to what the 9.6 µm channel actually senses in the upper
troposphere and lower stratosphere though it is probably best characterised as an observation of
lower stratospheric ozone. TOVS is quite insensitive to middle- and upper-stratospheric ozone.
However, it does provide data during the polar night which is not possible with either TOMS or
GOME because they require the presence of solar radiation to make measurements; TOVS
exploits emission and can therefore work in darkness.
3.3.2 Currently Planned Operational Satellite Systems
This section considers satellite programmes planned for the near future which are intended
to help satisfy requirements for the operational provision of these data on a long term basis. It also
outlines some variants of current experimental instruments which may find operational application.
Additional SBUV instruments are planned for future NOAA polar orbiting meteorological
satellites with afternoon equatorial crossing times; currently scheduled launch dates are shown in
Figure 3.5. Utimately, these instruments will be replaced by GOME-2, OMI, and OMPS which have
superior performance.
Table 3.5 provides details of the species observed by each of the operational systems
described below together with an indication of their performances. Again, in referring to this table,
it is important to remember that system performance is very dependent on orbit characteristics.
a) The Stratosphere Aerosol and Gas Experiment (SAGE III) is an improved version of
the SAGE instrument, with higher spectral resolution and greater spectral wavelength
coverage. It will also have a lunar occultation capability which will allow observations to be
made over a broader range of latitudes than are available from solar occultation alone
(especially in sun-synchronous orbits where solar occultations are confined to high
latitudes). Its lunar occultation capability should enable it to make measurements of NO3
and OClO which are present almost exclusively at night because of their rapid daytime
photolysis (temperatures will not be available in this mode of operation).
As compared with previous SAGE instruments, this version has an ultraviolet
channel (290 nm), which can be used for the improved detection of ozone in the upper
atmosphere, and an additional near-infrared channel (1.5 µm) that can provide information
on the distribution of aerosol in the cloud-free troposphere. Temperature information is also
included through the observation of the molecular oxygen A band (near 762 nm); these
measurements will facilitate the conversion of measurements to the desired mixing ratio
versus pressure co-ordinate system (rather than the observed number density versus
altitude one).
In order to provide a better geographic coverage (given the inherent coverage
limitation of solar occultation), the goal is to have one SAGE instrument flying in an inclined
orbit and another in a sun-synchronous polar orbit. Currently planned flights are aboard a
Russian Meteor-3M (polar sun-synchronous orbit) in mid-2000 and the International Space
Station (51.5 degree inclination orbit) in early 2001. A third SAGE III instrument is currently
under construction for use aboard a platform still to be decided.
b) The Global Ozone Monitoring Experiment (GOME-2) is similar to GOME with slightly
better accuracy and better spatial resolution, but the same vertical resolution. The
improvements mainly relate to improvement in performance (i.e. accuracy) rather than the
number of atmospheric variables observed. Like GOME, the GOME-2 instruments will be
ultraviolet/visible, nadir-viewing instruments exploiting a combination of the SBUV and
spectroscopic fitting techniques to observe a range of atmospheric variables, far wider than
any of the other instruments described above (see Table 3.3).
The GOME-2 instruments will be flown on the METOP series of meteorological
satellites which have a total planned life time of fifteen years. They will fly in the “morning”
polar orbit, METOP being the European operational replacement for the current series of
42
NOAA operational meteorological satellites. This is a joint ESA/EUMETSAT programme
with the launches planned for 2003, 2007, and 2010.
c) The Infrared Atmospheric Sounding Interferometer (IASI) is also part of the core
payload of EUMETSAT Polar System (EPS) METOP-1 and will contribute to the primary
mission objective of EPS which is the assessment of meteorological parameters. The
AMSU-A and MHS microwave sounding systems, the HIRS/3 infrared sounder and the
AVHRR/3 imager are all companion instruments of the meteorological payload. It will
operate from a low altitude, sun-synchronous polar orbit, over a 2000 km wide swath.
The main focus of IASI is the provision of temperature profiles with improved
accuracy and vertical resolution compared with the currently existing infrared temperature
sounder HIRS on the NOAA polar satellites. To achieve this goal a high spectral resolution
is required, and a novel instrument was designed based on a Michelson interferometer. It
-1
will cover the spectral range from 645 to 2760 cm with a spectral resolution (unapodised)
-1
between 0.25 and 0.5 cm .
Among the parameters that will be measured with IASI, either in a stand-alone or in
a synergistic mode with other EPS instruments, are, in addition to temperature profiles,
water vapour profiles, surface characteristics (i.e. temperature, emissivity), cloud
parameters (top pressure and temperature, effective amount) and column integrated and
vertical information on some minor constituents (O3, CO, CH4, N2O, SO2).
d) The Ozone Mapping and Profiling Suite (OMPS) is a two-instrument combination
being planned for the US National Polar Orbiting Environmental Satellite System
(NPOESS) series of polar orbiting spacecraft. The OMPS instrument is still under definition
though provisional instrument specifications have been listed. These envisage the OMPS
instrument providing full daily global mapping of total column ozone amounts with a
horizontal resolution of 50x50 km at nadir (or better), and vertical profiling (no mapping)
with a vertical resolution of at least 5 km; with an objective of 3 km vertical resolution.
The vertical profiling resolution requirement rules out a nadir-viewing instrument;
therefore the OMPS instrument will include both a nadir-viewing total ozone instrument
(using a push broom technique) and a limb-viewing vertical profile instrument using the
limb scattering technique in the ultraviolet, the visible and the near-infrared.
The first NPOESS spacecraft with the OMPS instrument is not expected to fly
before 2009, although the actual launch date could vary in the range 2007-2010 depending
on the operational conditions of the remaining NOAA polar orbiting spacecraft (such as
NOAA-N). It is currently expected that NPOESS will continue the spectrally resolved and
total solar irradiance measurements using the instrument currently operating aboard UARS
and planned for the SORCE mission (see Annex E).
e) The Stationary Visible/Infrared Imager (SVIRI) will fly on the Second Generation
Meteosat (MSG) series of satellites; the first is due for launch in 2001 and they have
planned lifetimes of 15 years. These will be operational meteorological satellites flying in
geostationary orbit above the Greenwich meridian. They will replace the current series of
Meteosat satellites.
SVIRI will represent a significant advance on the current Meteosat imager, having 5
channels in the visible and 5 in the infrared. One of the latter (at 9.7 µm) is intended to be
used to observe the distribution of ozone though not to the accuracy attainable with GOME
or SAGE. It will have a horizontal resolution of about 3 km.
43
3.3.3 Current and Projected Research Satellite Systems
This section outlines four major research missions of sufficient duration to provide long
term data sets relevant to the Ozone Project. In addition to the actual provision of data,
experimental satellite missions also point the way to the future by providing a test bed for new
operational instruments.
a) The Upper Atmosphere Research Satellite (UARS) was launched in September, 1991
to study the chemistry and dynamics of the Earth’s stratosphere and mesosphere, as well
as solar radiation and particle forcing of the Earth-atmosphere system. UARS has a total of
10 instruments, all but two of which are still working. UARS instruments may be broken
down into several categories - atmospheric chemistry (Halogen Occultation Experiment HALOE, Microwave Limb Sounder - MLS, Cryogenic Limb Array Etalon Spectrometer CLAES, Improved Stratospheric and Mesospheric Sounder - ISAMS), atmospheric
dynamics (High Resolution Doppler Interferometer - HRDI, Wind Imaging Interferometer WINDII), solar irradiance (Solar-Stellar Irradiance Comparison Experiment - SOLSTICE,
Solar Ultraviolet Spectral Irradiance Monitor - SUSIM, Active Cavity Radiometer Irradiance
Monitor - ACRIM), and particle input (Particle Environment Monitor - PEM). All except two
of these (CLAES, ISAMS) continue to operate after more than eight years. UARS provides
0
continuous coverage equatorward of 34 but only views higher latitudes half the time
(viewing northward or southward in approximately 36 day increments).
The present focus of UARS is to document long term changes in the upper
atmosphere together with solar and particle forcings. In particular, the continuing
measurement of the vertical profile of ozone, key source and reservoir gases, and
temperatures, as well as the UV solar spectral irradiance have provided valuable data sets
for the study of both long term trends and interannual variability in the stratosphere.
b) The ENVISAT mission will fly in 2001 and includes three instruments focused on
atmospheric chemistry. These are the Scanning Imaging Absorption Spectrometer for
Atmospheric Cartography (SCIAMACHY), the Michelson Interferometer for Passive
Atmospheric Sounding (MIPAS), and the Global Ozone Monitoring by Occultation of Stars
(GOMOS) instruments. SCIAMACHY is a multi-wavelength (240-1750 nm, 1.9-2.4 µm),
multi-viewing geometry (limb/nadir/occultation) instrument designed to measure the column
and profile distribution of a number of gases, including high horizontal resolution
measurements of ozone.
MIPAS, a high spectral resolution limb sounder, operating in the wavelength range
from 4.15-14.6 µm, will provide measurements of vertical profiles of more than 20 species
(especially nitrogen-containing species), as well as pressure/temperature, aerosols, and
PSCs. GOMOS will use the stellar occultation technique to measure ozone profiles and the
possibility to retrieve NO2, NO3, H2O, and aerosol extinction profiles. Since there are very
many stars to use as light sources, the stellar occultation technique has the potential to
provide much more complete spatial coverage than is available from solar occultations, so
measurements at nearly all latitudes are possible even though ENVISAT will be in a polar
sun-synchronous orbit. An operational version of this instrument is under consideration (i.e.
COALA).
ENVISAT will fly in a high inclination, sun-synchronous orbit at an altitude of 800
km. The local mean solar time in the descending node will be 10:00 hrs. The planned
mission duration is five years. Both MIPAS and SCIAMACHY will provide global coverage;
the coverage of GOMOS will depend on the distribution of occultation targets.
c) The EOS-Aura mission which is planned for launch in mid 2003 will have four
instruments dedicated to the study of atmospheric chemistry. These include the
Tropospheric Emission Spectrometer (TES), the Microwave Limb Sounder (MLS), and the
High Resolution Dynamics Limb Sounder (HIRDLS), and an ultraviolet mapping
spectrometer for study of total column and profiles of ozone known as the Ozone
44
Monitoring Instrument (OMI). TES is a high spectral resolution instrument designed to
observe both tropospheric ozone and its precursor nitrogen dioxide. It will have both a nadir
and a limb mode, and will also provide information on a number of constituents in the lower
to middle stratosphere.
MLS is a significantly enhanced version of the UARS MLS instrument and will
measure a number of constituents in the stratosphere and upper troposphere, including
OH. By virtue of measuring the distribution of OH, ClO, BrO, and several nitrogen oxides,
MLS will provide the first global information on catalytic ozone destruction by all important
chemical families in the stratosphere.
HIRDLS is an infrared emission instrument designed to measure stratospheric trace
constituent and temperature distributions at high horizontal and vertical resolution, and
should provide information on small-scale variability in the atmosphere for use in transport
studies. A primary focus of HIRDLS is the study of long-lived trace gases that most clearly
reflect atmospheric transport processes, although HIRDLS will also measure several
chemical reservoir species as well.
The OMI is a hyperspectral nadir viewing instrument with daily global coverage and
spatial resolution of 13x24 km for total ozone column. Additional parameters, such as those
measured by GOME (see Section 3.3.1) will also be measured by OMI but at somewhat
reduced spatial resolution over that which it achieves for total ozone.
EOS-Aura will fly in a 750km orbit with a 1:45 PM equatorial crossing time. Since
TES, MLS, and HIRDLS are emission instruments, coverage of the entire Earth will be
provided by these instruments. OMI, which uses a scattering technique, only obtains data
over sunlit areas so no coverage of polar night is provided. The instruments and spacecraft
are designed for five years.
d) The GCOM-A1 programme of Japan will consist of two instruments for atmospheric
chemistry flying aboard a satellite in an inclined non sun-synchronous orbit planned for
launch in 2006. The first of these instruments is the Ozone Dynamics Ultraviolet
Spectrometer (ODUS), a grating spectrometer covering the wavelength range from 306 to
420 nm with 0.5 nm spectral resolution and ground resolution of 20x20 km at nadir. It is
designed to measure the column amounts of ozone, aerosol, SO2, NO2, BrO, and OClO
(similar to GOME and OMI). The second instrument is a follow-on to the second Improved
Limb Atmospheric Spectrometer (ILAS-II) planned to fly aboard ADEOS-II in 2001. This
follow on instrument will improve on the ozone, aerosol, and trace constituent profiles made
by its predecessors. It is planned to complement the GCOM-A1 payload with a third
instrument. The GCOM-A1 spacecraft is planned for operation until 2010.
In addition to these three major missions there are several other missions that can provide
information of relevance to the Ozone Project. These missions are more concerned with process
studies than monitoring. They are listed in Annex E.
3.3.4 Observations from Non-Low Earth Orbits
Finally it is relevant to highlight the role of space-borne instruments making observations
from satellites flying on non-low Earth orbits as, in particular, they offer the opportunity to
increase temporal coverage. This is important as there are large diurnal variations in the
emission of pollutants which are associated with the photochemical production of ozone in the
planetary boundary layer and free troposphere. The levels of ozone produced are high.
The production of tropospheric ozone and photochemical smog typically peaks in the midto-late afternoon. NO2 emissions follow traffic and energy use patterns. The time scale of the
oxidation of SO2 yielding H2SO4 which acts as condensation nuclei for aerosol and cloud
formation, is similarly short. Biogenic emissions also have complex emission patterns increasing
when the temperature rises but also being strongly dependent on levels of humidity. Both
determine the rate of opening of stomata. Comprehensive measurements of air quality on urban,
45
regional, continental, and global scales impose stringent requirements on space-borne
observations with a focus on the upper troposphere.
High temporal and spatial resolutions are required to determine accurately the emission
rates of pollutants from industrial pollution, biomass burning and biogenic emissions to the
atmosphere. These measurements are also necessary to assess the impact of anthropogenic
activity on air quality and for meteorological applications. Excluding latitudes above about 70°,
remote sensing instrumentation on sun-synchronous low Earth orbits (LEO) can only observe the
same location at the same local time at best once a day. This may be contrasted with
instruments mounted on geostationary platforms which can observe continuously approximately
0
0
one third of the globe, from about 65 N to 65 S. A further observing location is the so-called L1
orbit, which enables the whole Earth to be observed about once a day.
In order to obtain global coverage having the required spatial and temporal resolution a
fleet of LEO satellite-borne instruments (approximately 14) is needed. The same data set can be
generated by instruments aboard three geostationary platforms, separated by 120° in longitude.
In theory one instrument in a L1 orbit can also provide the same information. On the downside it
is important to remember that the geostationary orbit is approximately 40 times further from the
Earth than the LEO and the L1 orbit is further away still. Thus a passive remote sensing
instrument in L1 requires a relatively large telescope and launcher. The TRIANA mission now
planned for 2002 launch will be the first Earth science mission to test this vantage point.
Instruments in geostationary orbit are attractive for the transcontinental monitoring of
pollution and biomass burning. Observations of quite high spatial resolution are possible from this
orbit if the ability to “stare” continuously at a particular location is used to increase signal-to-noise
ratios. A combination of three geostationary platforms, as has been employed for meteorological
observations, would provide the requisite global coverage. This geostationary perspective has
not yet been exploited to monitor air quality though several missions are now under study to
evaluate this unique vantage point. These are described in Annex E.
Currently there is an experimental TOZ total ozone column product available from the
NOAA GOES platform which is similar to the TOVS product. It is only obtained in non-cloudy
fields-of-view but it is produced many times a day.
46
4.
4.1
HARMONISATION OF PROVISIONS AND REQUIREMENTS
Introduction
In this chapter the user requirements (see Chapter 2) are compared with current data
provisions (see Chapter 3). This assessment takes account, not only of the provision and
capabilities of space-borne instruments but also those of the other elements of the observing
network i.e. ground-based and airborne. Chapter 6 highlights the main conclusions and
recommendations that emerge from this exercise.
The provision of the large number of measurement systems described in Chapter 3 goes a
long way towards helping to satisfy the requirements outlined in Chapter 2. However, in addition to
addressing individual requirements, there is a critical overarching requirement that the Ozone
Project must satisfy, namely the need for:
•
•
accurate long term calibration.
continuity of data provision with overlap in case of instrument change;
The first requires regular calibration (traceable to international standards) and validation of
derived geophysical parameters over the lifetime of a sensor or observing system. It is essential to
avoid gaps in data streams, inconsistent calibration between instruments and long term drifts in
instrument performance. It is also important to ensure the proper harmonisation of ground and
space-based systems. The quality of ground-based observations and their spatial representivity
must be documented.
The second requirement represents a particularly challenging issue for space-based
systems as it may prove prohibitively expensive to try to ensure the provision of systems
sufficiently robust to safeguard continuity in case of failures (including launch, spacecraft and
instrument failures) for anything beyond a very limited set of parameters. Some prioritisation of the
need for continuity of observation of different parameters must be established.
There are two different measurement protocols covering the required parameters,
summarised as:
monitoring – long term continuous measurement by a series of closely related and regularly
intercalibrated instruments;
regular observation - continuity of measurement is desired but there is a much greater
tolerance for gaps in data records.
Thus, species such as the chlorofluorcarbons with very small spatial and temporal variation
may only require periodic observation from space for long term characterisation, while a trace gas
such as ozone must be continually monitored.
The other point that must be highlighted is the need to view all the various components of
the observing system. Thus, in the sections that follow, in addition to considering each system in
its own right, the composite picture is assessed in the light of the requirements detailed in Chapter
2. The question of the calibration and validation of space-borne instruments is addressed in
Chapter 5 Calibration and Validation.
4.2
Total Column Ozone
4.2.1 Ground-Based Measurements
The current ground-based measurement programme for total ozone column amounts is
adequate for providing long term, well calibrated measurements of column amounts for monitoring
stratospheric trends. However, there are difficulties in ensuring continued support for the operation
of some of the existing stations as in several instances only minimal funding is available. Unless
47
this is corrected it will ultimately compromise the quality of the data, especially if resources
become inadequate to support participation in calibration-related activities.
The elements of the current network are deployed in areas where support from national
agencies is available, that are logistically convenient for operation and, as a result, are not well
distributed geographically. In particular, there is a lack of sites in the tropics and Southern
Hemisphere. The provision of funding for establishing networks in the tropics and Southern
Hemisphere is a challenge for the international community which must be resolved in the very near
future.
4.2.2 Space-Based Measurements
Space-based measurements of total and profile ozone amounts form one of the most
important IGOS data sets although they mainly reflect changes in stratospheric ozone. No single
observing technique fully meets user requirements so it is necessary to exploit the capabilities of
complementary observing systems.
For example, there is excellent complementarity between the TOMS technique which uses
a limited set of wavelengths but provides data with excellent spatial resolution, and the GOME
approach which can observe a much larger set of wavelengths but at reduced spatial resolution.
Because of their enhanced spectral coverage, the GOME-type instruments have the potential to
make more accurate observations than TOMS.
The plans currently in place by the space agencies go a long way towards meeting the
requirements listed earlier. Two major polar orbiting programmes are already in place:
•
•
The US programme of TOMS (one flying now, one planned for launch in 2000), the
Dutch OMI instrument on EOS-Aura in 2003 and the OMPS instrument planned for
NPOESS (beginning in 2007-2010).
The European programme of GOME (currently flying on ERS-2), SCIAMACHY
(planned for 2001 on ENVISAT) and GOME-2 and IASI (planned for 2005 and beyond
on the METOP series of operational satellites).
In addition, there is NOAA/SBUV/2 which is a major operational programme currently in
place. METOP and NPOESS will be fully operational programmes (after the launch of METOP-2
there should always be a "hot" spare available in orbit) and ENVISAT will supply products
operationally. The provision of operational products from EOS-Aura is being considered.
A gap in the US series could occur prior to 2010 if the NPOESS OMPS instrument does not
fly prior to the end of the expected period of operation of the OMI instrument on EOS-Aura (late
2007 assuming a late 2002 launch). In such a case, the global observing system would depend on
the instruments flown on the METOP/GOME-2 and the POES/SBUV/2 which do not provide the
spatial coverage to meet all requirements (Chapter 2).
If the first NPOESS/OMPS launch does not occur till the end of its potential launch window
an alternative strategy must be considered. One possibility would be an early flight of the OMPS
instrument. The Japanese GCOM-A1/ODUS which is planned for 2006 to 2010 would be a good
candidate to fill this gap. However, the GCOM-A1 orbit is not sun-synchronous and therefore
cannot meet the spatial requirement.
From geostationary orbit only Meteosat Second Generation (MSG) includes an ozone
monitor (from 2001). This will be based on an infrared emission nadir-viewing technique and has
quite a lot in common with TOVS. These data are not strictly compatible with those from
ultraviolet-based nadir-viewing systems so intercomparisons will be essential. The inclusion of
similar (or ultraviolet) instruments on some of the other geostationary satellites would be a very
good idea as a combination of polar orbiting and geostationary systems is required to ensure the
proper combination of geographic and temporal coverage.
48
Overall the situation is quite encouraging provided NPOESS OMPS is not delayed.
Exploitation of geostationary missions will provide a unique opportunity to strengthen temporal
coverage.
4.3
Ozone Vertical Profile
4.3.1 Ground-Based Measurements
In the stratosphere the ground-based measurements of vertical profiles of ozone which are
of most relevance to the Ozone Project are the lidar and Umkehr observations (based on the
Dobson and Brewer instruments), though currently only a limited number of Dobson instruments
are being used for Umkehr observations. A first priority must be to ensure the continuation of
Umkehr observations from those stations with long data records. However, the initiation of new
Umkehr observations is also necessary as geographic coverage is currently limited.
Lidar instruments have the potential to provide high resolution, well calibrated, observations
of ozone profiles in the stratosphere and will undoubtedly increase in importance in the future.
Many of the lidar observing systems are already affiliated with the NDSC. This is important as
adherence to NDSC protocols undoubtedly helps to ensure the overall consistency of data quality.
The current ozone lidar network is not well distributed geographically and the provision of
additional lidar sites in the tropics and Southern Hemisphere is very important.
In the troposphere, lidars are principally able to provide high resolution information on
ozone profiles so, given the increasing importance of tropospheric ozone data, the provision of
additional lidar instruments and their intercomparison must be viewed as a priority. These should
also be affiliated with the NDSC and WMO-GAW. The contribution of these observing systems will
undoubtedly increase as they become more widely distributed (possibly associated with their
expanding use in air quality monitoring programmes). They would also prove very useful in helping
to validate space-based tropospheric ozone profiles.
The microwave spectrometers included in the NDSC can also be used to observe vertical
profiles of ozone. These instruments are fairly unique as they can provide information day and
night (this also makes geophysical validation easier). The provision of these data together with
observations of some important related trace constituents, notably chlorine monoxide, water
vapour and nitrous oxide, is of great importance. It is essential to ensure the continuation of high
latitude observations made with these instruments (especially in winter) as they are the best
source of these data.
The main concerns here are to improve the geographic distribution of the lidar stations,
notably in the Southern Hemisphere and in the tropics, and to increase the number of such
stations affiliated with the NDSC.
4.3.2 Balloon- and Aircraft-Based Measurements
An extremely critical element of an integrated system is the maintenance of the balloonbased ozone sonde programme, whose importance was noted earlier (Chapter 3). Apart from
ensuring the continuation of the current system, the main priorities are the expansion of the
network in the tropics and Southern Hemisphere, the continued focus on calibration and
intercomparison according to the WMO-GAW programme (especially if new types of instrument
are introduced) and the development of new improved instruments that correct some of the
deficiencies of current instruments.
Some progress has been made in improving the availability of ozone sonde data in the
tropics but much of this is on a temporary basis. The development of a long term international plan
to ensure the continued operation of ozone sondes in the tropics is a top priority as, at present,
there is a strong possibility of the data base being terminated or drastically reduced. For ozone
sonde data to be useful for trend determination, a measurement frequency of at least twice
49
monthly is needed, with weekly flights being preferable. The expansion of regular ozone sonde
flights to several geographic areas, where there are few or no regular data (i.e. South America,
Africa, all regions of the former Soviet Union and the Middle East), would be a major enhancement
to the current international observing programme.
Calibration is also an issue as the use of different types of ozone sondes in different
locations, combined with the effects of variations in sonde preparation on their use, means that the
different groups must regularly intercompare sondes (both in actual use and in controlled
chambers). Support for this type of activity has been limited in the past. Steps must be taken to
ensure their continuation and regular implementation. Intercomparisons with lidars is equally
important. This topic is discussed in detail in Chapter 5.
Finally, it is necessary to focus efforts on the development of improved ozone sondes,
especially if they can be made smaller, simpler and/or cheaper, to facilitate increased use. This
could be an excellent goal for technology programmes. Current problems include requirements for
pump efficiency corrections and the need to “normalise to Dobson” by comparing integrated total
ozone profiles with those obtained from nearby Dobson stations.
Routine operational aircraft observations, such as those within the MOZAIC programme,
should continue and be expanded because of their ability to characterise the tropopause region,
especially at mid-to-high latitudes (the tropical tropopause is well above the altitude range
accessible to today’s commercial aircraft). Some expansion of the programme to improve the
spatial distribution of measurements would be very useful, especially when this means that these
data span several ozone sonde and/or lidar locations.
Again the main concern is the lack of coverage in the tropics and in the Southern
Hemisphere, though in assessing the requirement the provision of lidar stations must be taken into
account. Routine operational aircraft observations should also be expanded and the development
of improved ozone sondes considered.
4.3.3 Space-Based Measurements
Space-based vertical profile measurements of ozone are not nearly as well in line with
requirements as is the case for total ozone column amounts. The current situation is complex several instruments associated with long term measurement programmes measure the vertical
profile of ozone in the stratosphere and in the cloud-free upper troposphere, but none has all the
desired characteristics (i.e. good vertical resolution, good spatial coverage). Candidate solutions
for the stratosphere include ultraviolet/visible limb scattering (proposed for NPOESS) and
microwave/infrared emission. In the troposphere proper, the problem is even more acute as only
limited data are currently available and vertical resolution is coarse except near the tropopause. A
pressing requirement is the development of instruments capable of redressing this deficiency.
Those instruments with good vertical resolution (e.g. SAGE II and soon SAGE III) tend to
have limited spatial coverage because of their reliance on solar occultation, while those with better
spatial coverage (e.g. SBUV/2 and OMI) lack vertical resolution, especially in the troposphere and
lower stratosphere. For the future, instruments based on the stellar occultation technique (e.g.
GOMOS) may strike a reasonable compromise between these two extremes though, as indicated
above, there are other possibilities including limb viewing infrared and microwave instruments.
However, none of these techniques appears capable of meeting requirements in the troposphere.
Many of the current instruments are operating well beyond their anticipated lifetimes, for
example, SAGE II has been operating since 1984. SAGE III instruments are planned for launch
but the first of these instruments (as the current POAM-3 instrument) will fly in a polar sunsynchronous orbit so that solar occultation will be limited to high latitudes. Lunar occultations made
with this instrument will provide some tropical and mid-latitude data but these must be considered
as experimental until successfully demonstrated using actual SAGE III data (SCIAMACHY should
also help clarify the potential of this approach).
50
The next SAGE instrument in an inclined orbit, planned for the International Space Station
(ISS), will not be launched until 2002 and will suffer from some loss of data due to downtime
associated with Shuttle visits as well as the limited viewing capabilities available from the ISS. An
additional SAGE III instrument is being constructed, but no flight opportunity has yet been
identified.
The SBUV/2 situation is mixed as the NOAA-14 instrument has problems with its grating
drive and the solar diffuser is not operational on the NOAA-11 instrument (this limits calibration for
ozone profiles). The SBUV/2 instrument launched in September 2000 will overlap NOAA-9 and
NOAA-11, and will be major sources of archival information on ozone changes in the upper
stratosphere.
A significant contribution should ultimately be made by the GOME instrument on ERS-2
which is just starting to return ozone vertical profiles. Although these must still be considered as
research products, operational products may shortly become available. Reprocessing should
ensure the availability of these data back to 1995 and support the requirements for trend detection
stated in Chapter 2. Mention must also be made of SCIAMACHY, OMI and GOME-2, especially
the latter which will fly on an operational series of satellites. Together these instruments (also with
OSIRIS and SMR on ODIN) should ensure data continuity from 1995 to at least 2010. However,
given the importance of these data, there is still a need for a high vertical resolution (with good
global coverage) operational ozone profiler, such as is planned for NPOESS (OMPS), that can be
flown on a regular basis.
Over the next few years a number of ozone-profile measuring research-oriented
instruments will be launched. Several of these (notably MIPAS, HIRDLS and MLS) should provide
the desired combination of vertical resolution and spatial coverage (though the troposphere will
remain a problem). However, these instruments are all complex and not well suited to long term
operational use. Significant effort will have to be devoted to the construction of a unified data set
which includes data from these and any predecessor instruments that may overlap with them.
SCIAMACHY, in its solar, lunar occultation and limb scattering modes, will provide profiles
to the desired vertical resolution in the stratosphere and upper troposphere though, like SAGE,
with limited geographic coverage. GOMOS has the potential to provide both good vertical
resolution and reasonable geographic coverage. However, this will be the first routine
implementation of stellar occultation (currently limited to a small number of observations by UVISI
which are not generally available) so its role in ensuring a continuous data set cannot be taken for
granted. An operational version (COALA) is on the drawing board which could be implemented if
GOMOS lives up to expectations.
Overall the situation is complex as there is no single instrument (or group of instruments)
capable of fully meeting the requirements, notably for good vertical profiles in the troposphere. It is
also disturbing that the flight opportunities required to exploit SAGE III are still not confirmed.
4.4
Meteorological Parameters
Although another of the CEOS projects (i.e. the Upper Air Project) in support of IGOS will
be providing requirements for most of the meteorological variables relevant to the Ozone Project
(i.e. temperature, wind, cloud information, water vapour concentrations/specific humidity, etc.), it
does not per se consider the requirements of the Ozone Project for these data. In most instances
this does not pose a problem but there are some instances where the Ozone Project's
requirements for meteorological information are stricter than those required to meet the objectives
of the Upper Air Project. These are considered in this section but, without doubt, the most serious
concern is the provision of adequate observations of water vapour in the upper troposphere and in
the stratosphere, and the precise location of the tropopause.
51
The discussion in the ensuing sections does not implicitly refer to the contribution of the
operational radiosonde network. These sondes are capable of measuring all these parameters to
the requisite accuracy but are restricted in geographic coverage, notably in the tropics and in the
Southern Hemisphere. Programmes such as MOZIAC help to resolve the coverage problem over
the oceans in the Northern Hemisphere but the rest of the globe remains a problem. It is also clear
that GNSS occultation data have a vital role to play, assuming these data are properly assimilated.
4.4.1 Upper Tropospheric and Stratospheric Water Vapour
Although the Upper Air Project has listed requirements for water vapour profiles in the
upper troposphere, these are inadequate for the Ozone Project. In particular, the climate and
weather oriented focus of the Upper Air Project has led to these requirements being stated in
terms of specific humidity. This makes sense in the lower and middle troposphere where water
vapour amounts are reasonably large, but is of little use in the upper troposphere where the
concentrations are extremely small (lower ppm-range). Here a small uncertainty in specific
humidity can correspond to an enormous uncertainty in relative humidity.
The stricter requirements placed on upper tropospheric and stratospheric water vapour
near the tropopause (see Annex B; Table B.2a) impose a significant constraint on measurement
systems. In particular, the large change in water vapour mixing ratio with altitude, especially near
the top of the tropospause, means that high vertical resolution is of critical importance if the
observations are to prove useful within the context of the Ozone Project. Here ground-based
lidars, capable of measuring water vapour profiles, should play a very useful role.
The operational space-borne meteorological sounders are not designed to meet these
requirements. However, limb-viewing chemically-oriented profilers such as MIPAS, HIRDLS,
SCIAMACHY and MLS do have the capability but all are non-operational instruments and long
term data continuity is not anticipated. Another possibility is the combination of GPS/MET data with
independent temperature observations which has considerable potential for meeting the ozone
Project's requirements.
To date the most important long-heritage measurements of water vapour in the lower
stratosphere and upper troposphere are those emanating from HALOE (since September 1991)
and SAGE II (covering mainly the pre-Pinatubo period when aerosol contamination was small; reinitiation of the SAGE II water vapour measurements once stratospheric aerosol loading has
declined (after 1995) should be feasible though the revised SAGE algorithm is not yet available.
However, both these instruments are well past their planned lifetimes. The logical step would be to
seek the continuation of one or both of these occultation-based measurements.
The SAGE III instrument planned for the ISS should provide tropical and mid-latitude
coverage (though viewing will be limited - see earlier). High latitude observations will be provided
by SAGE III, POAM-3 and ILAS-2, but long term measurements are not guaranteed.
4.4.2 Stratospheric Temperatures
The need for accurate temperature information throughout the stratosphere is clearly
essential to the Ozone Project and here again the requirements are stricter than those formulated
by the Upper Air Project. These temperature data are also required to convert the observations
made by occultation-viewing instruments (they actually observe number density versus altitude)
into the more scientifically useful mixing ratio versus pressure co-ordinate system. However,
fortunately, most of the newer occultation sensors make simultaneous measurements of
temperature (e.g. SAGE III, POAM-2) so normally there would be no need to look to externally
supplied temperatures.
52
Several of the existing measurement systems can provide the requisite stratospheric
temperature information, including lidars, GNSS occultation, radiosondes and essentially all
infrared- and microwave-based satellite instruments (though not all on an operational basis) and a
sensor onboard MOZAIC. The oxygen A-band absorption technique which is already being used
on several satellite systems (e.g. GOMOS and SAGE III) will also provide temperature profiles.
Also, if successfully implemented, ultraviolet limb scattering (SCIAMACHY) could also help ensure
the provision of the requisite observations of stratospheric temperatures (air density and ozone
must be retrieved together) as will research-oriented instruments exploiting emission techniques
(e.g. HIRDLS, MLS and MIPAS). Given this multiplicity of sources it appears that most of the
stratospheric temperature needs for ozone applications should in principle be met, at least during
ENVISAT and EOS-Aura.
4.4.3 Tropopause Height and Temperature
The interpretation of long term records of ozone amounts (especially total ozone column
amounts) requires the height of the tropopause to be accurately known as there is a strong
correlation between tropopause height and ozone column amounts. Even a very small change in
tropopause height would, if it continued for an extended period of time, have an effect on derived
ozone column amounts which might be confused with actual chemically-generated changes.
The needed precision (i.e. tropopause height known to approximately 100 m; year-to-year
consistency to about 50 m - see Chapter 2) requires the long term availability of lidar, radiosonde
and/or GNSS occultation data. No other measuring systems can be expected to provide the
requisite accuracy and stability of observation of tropopause height. As noted earlier, the
geographic distribution of lidar stations is limited, especially in the tropics and Southern
Hemisphere, though GNSS occultation should provide good global coverage. Continued support
for both systems would ensure the availability of good global information to the requisite accuracy.
The temperature of the tropopause is also a required parameter. This should be obtained
to sufficient accuracy by any temperature profiling system meeting the requirements specified by
the Upper Air Project (using the WMO definition of tropopause). Here specific mention must be
made of the IASI and AIRS instruments. The former will fly on the operational METOP satellites.
4.4.4 Cloud Top Height and Cover
As far as the Ozone Project is required, the main justification for observations of cloud top
heights (and coverage) is for use in the accurate retrieval of ozone information from instruments
with nadir-viewing geometry and for estimating UV fluxes at the ground. The most important
requirement placed on observations of cloud top height and coverage is the co-registration of
cloud top heights with ozone measurements (especially total column amounts).
This can be achieved in one of two ways - either as part of the measurements made by the
ozone instrument itself, for example, through measurement of the oxygen A-band at 762 nm or at
shorter wavelengths (such as 393-397 nm) through the Ring Effect or by the inclusion of another
instrument (i.e. lidar) on the same platform as the ozone measuring instrument.
Some of the available and projected instruments (e.g. SAGE III, GOME, OMI and
SCIAMACHY) have sufficient spectral range and wavelength resolution for cloud top heights to be
derivable from the instrument’s data alone. The same will be true of GOME-2 on METOP, an
operational system which includes IASI, another source of cloud height information. The imager on
METOP will of course provide high quality images of clouds as will the NPOESS instrument. Cloud
cover should prove no problem.
53
4.5
Related Chemical Constituents
A list of related chemical constituents that are needed to interpret ozone changes was
presented in Chapter 1. This was based on the assumption that the actual requirement is for
continued observations of a small number of key parameters whose concentrations can be related
to those of other constituents through chemical models.
The requirements listed in Chapter 2 are, at least for the stratosphere, quite well addressed
by planned space and ground-based measurement systems. However, there is a problem
ensuring the long term continuity of observation of some of the parameters which will be measured
from ENVISAT and EOS-Aura but not from the planned operational systems. Follow on research
space platforms are only being considered.
For many of these chemical constituents the observing requirements are more in the vein
of “continuous” observations rather than “monitoring” (see earlier). This means that small gaps in
data records, instrument-to-instrument variability and long term drift can be tolerated provided
biases and precision are compatible with the detection of small changes. This is not generally the
case for ozone column and profile measurements (or for temperature profiles).
4.5.1 Associated Trace Constituents
a)
Surface-Based In Situ Measurements
The major requirement that must be met by surface-based in situ measurements is the
need for very accurate determination of concentrations of CFCs, halons, CFC replacements, other
halocarbons (including methyl chloroform, carbon tetrachloride, methyl bromide) and other
chemically and radiatively active source gases (e.g. nitrous oxide, methyl bromide). Existing long
term networks, notably WMO-GAW (e.g. AGAGE and the NOAA/CMDL flask sampling network),
perform well in this area and essentially meet the requirements listed in Chapter 2. However,
geographic coverage remains a problem.
It is clear that these activities, with their strong emphasis on ensuring consistency of
calibration over both the short and long term must continue. This means that all sites attempting to
document the long term evolution of surface concentrations of halocarbons and related species,
must engage in calibration tests, intercomparisons and data quality control (see Chapter 5).
Some expansion of the current network is essential if improved information about the
longitudinal distribution of sources of long life gases in the Northern Hemisphere is to be derived
from the surface concentration data (data from relatively industrialised areas in Europe and Asia
would be especially useful additions to the overall international network). There is also a need to
expand the data base in the tropics and in the Southern Hemisphere.
b)
Surface-Based Remote Sensing Measurements
Through its combination of sensing instruments the NDSC can provide information on all
the main trace constituents (see Table 3.1). This means that continued support for the NDSC is
crucial to documenting the long term evolution of the distributions of trace constituents. It is
especially true of total column amounts which are most easily measured with infrared and
ultraviolet/visible instruments.
Microwave radiometers also provide profile information on chlorine oxide (ClO) and other
species. Again some geographic expansion of the current network would be desirable through the
addition of complementary sites, especially in the tropics and Southern Hemisphere. However, it is
important to remember that only those sites that pay sufficient attention to long term calibration
can be considered as contributing to the overall requirement.
54
c)
Space-Based Measurements
The constituents considered in this section are those for which there is the greatest
need for continuous measurement from space (these are listed in Table 1.1). Not all these
need, in general, to be measured in the “monitoring” mode since their long term trend can
be reliably assessed from an expanded ground-based network (i.e. CO2, N2O, CH4 and
CFCs).
Nitrous Oxide ( N2O) and Methane (CH4) - Source Gases - currently planned instruments
will provide quite a lot of information on these two trace gases. Thus, observations of CH4
are currently being made with HALOE, and the planned MIPAS, SCIAMACHY, ILAS-2,
HIRDLS, MLS and TES instruments will all make measurements of the vertical distribution
of one or both of these constituents. The vertical resolutions of these instruments are more
in line with the threshold requirement (3 km) than the target value (1 km). HIRDLS,
because of its high vertical and horizontal resolution, probably comes closest to the
requirements listed in Chapter 2, at least for the stratosphere and upper troposphere.
In the lower troposphere where the variations in these constituents are fairly small against
a large background, the planned measurement systems will do less well though both
SCIAMACHY and MOPITT will observe CH4 column amounts as will IASI on METOP. Post
ENVISAT/EOS-Aura only the latter will continue. There are no specific NPOESS
requirements for these measurements.
Instruments exploiting infrared-based occultation have the capability to meet the
requirements but again there are no firm plans to develop operational versions of these
instruments, or for further flight opportunities. None of these instruments can meet the
requirements for tropospheric data
Carbon Monoxide (CO) - Source Gas - the most important historical set of measurements
of CO were made using the MAPS instrument flying on the US space shuttle though only
for short periods. Regular measurements from space will become available with MOPITT
on TERRA, SCIAMACHY on ENVISAT, IASI on METOP and TES on EOS-Aura. Beyond
that only IASI data will be available.
Carbon Dioxide (CO2) - Source Gas - CO2 measurements from space have thus far been
mainly used for determining atmospheric temperature profiles. With the possible exception
of SCIAMACHY, the accuracy of space-based CO2 observations is not sufficient to detect
smaller, short term changes in CO2, or to observe horizontal variations, though the larger
changes (factor of two) expected over the next century should be detectable. For current
trend detection, none of the sensors meet the requirements.
Hydrogen Chloride (HCl) -Reservoir - the vertical profile of HCl is currently being measured
by the HALOE instrument on UARS and will be measured by the MLS instrument on EOSAura. In addition there is the SMILES instrument on the International Space Station which
can also observe HCl (though with limited viewing capability - see earlier). Beyond this the
future is uncertain though the continued operation of a HALOE-like infrared occultation
instrument or a related instrument, such as an infrared Fourier transform spectrometer, in
an inclined orbit would go a long way towards satisfying the requirement.
An alternative approach would be the periodic flight of a suitable instrument (probably
exploiting infrared solar occultation) on the Space Shuttle, such as has been done with the
ATMOS instrument. As there is relatively little seasonal or spatial variation in the
distribution of this constituent near the stratopause, long term trends can in principle be
determined from a series of intermittent measurements. Here the self-calibrating nature of
occultation instruments would be a distinct advantage as this would help reduce the
uncertainty associated with intermittent observations.
55
Nitric Acid (HNO3) - Reservoir - so far satellite observations of HNO3 have only been
conducted on a limited basis, notably with HALOE on UARS. However these observations
would be useful in helping to clarify questions relating to polar stratospheric denitrification.
Some data should be provided by MIPAS on ENVISAT. The performance of TES on EOSAura will also be of interest as it should be able to observe HNO3 from the surface to
around 35 km. HNO3 will be adequately observed from HIRDSC on EOS-Aura.
Nitrogen Dioxide (NO2) and Nitric Oxide (NO) - Free Radicals - currently operating and
planned satellite systems should provide significant information on both NO and NO2.
HALOE and SAGE II use solar occultation to measure their profiles and GOME can be
used to observe total column amounts. Vertical profiles of NO and NO2 will also be
measured by several forthcoming instruments, notably SAGE III, POAM-3, SCIAMACHY,
GOMOS (+COALA), HIRDLS and TES. Total column amounts will be measured by GOME2, SCIAMACHY and OMI. For the long term, observations of column amounts is adequate
but the same cannot be said of profile information at high latitudes.
Denitrification at high latitudes is very important so it is vital to maintain profile
measurements at high latitudes to complement the measurements made using occultation
instruments in a polar sun-synchronous orbits. The current plan for this (involving POAM-3,
SAGE III and ILAS-2) will provide some measurements, but this is not very well coordinated (as evidenced by the unfortunate separation between the visible/ultraviolet
POAM-3 and SAGE III instruments and the infrared ILAS-2). ACE will now carry both an
ultraviolet/visible spectrometer and an infrared interferometer focusing on occultation
measurements on many gases related to polar processing. This is no assurance that
these measurements will be continued beyond ACE.
Chlorine Monoxide (ClO)- Free Radical - observations are currently being made with the
MLS instrument onboard UARS and will be continued with its successor onboard EOSCHEM. Additional observations should come from the microwave instrument aboard ODIN
and SMILES on the International Space Station (though with limited viewing capabilities).
However, given the importance of ClO, it is necessary to develop a long term plan for
ensuring the provision of continuous observations of ClO.
These need not be in the “monitoring” mode (as described above) as a continuous series
of high quality observations (with occasional gaps) should prove adequate given the focus
on examining inter-annual variations over the entire globe. The need for long term trend
information can perhaps be met by ground-based microwave radiometers associated with
the NDSC.
Therefore, the major need for ClO is to develop a plan for the continuation of vertical profile
measurements in the post EOS Aura timeframe. The requirement could probably be met by
the provision of a relatively focused microwave instrument. Another possibility is SMILES
on the International Space Station, though viewing will be limited and its orbit is
incompatible with the need to observe ClO in the polar regions.
Bromine Oxide (BrO) - Free Radical - the need for global observations of total column
amounts can be met to a certain extent by making observations in the ultraviolet/visible as
with GOME, SCIAMACHY and OMI. In the long term these data will be safeguarded by the
provision of GOME-2 (and its successors) on METOP.
56
5.
5.1
CALIBRATION AND VALIDATION
Introduction
To assure the scientific value of remote sensing measurements, calibration and validation
are critical activities; for deriving climate quality data sets they are essential. This is recognised by
the space faring nations who have and must continue to allocate resources for the calibration and
validation for Earth science research missions. For example, NASA’s UARS programme set aside
support for correlative measurements to validate most of its key data products. This effort provided
the essential credibility for UARS data which led researchers to use the data to make some major
scientific discoveries on the processes controlling stratospheric ozone. CNES played a major role
in the UARS correlative measurements programme. Their validation activities continued in support
of ILAS flying on NASDA’s ADEOS mission with several multiple balloon flights involving European
partners.
ESA’s ENVISAT mission, which includes three atmospheric chemistry instruments, has
initiated an international effort to establish a comprehensive calibration and validation programme.
NASA’s EOS-Aura mission, also carrying an international payload, will initiate and support a global
calibration and validation programme. These missions will rely primarily on the existing groundbased infrastructure (surface, balloon, aircraft and networks) to provide the needed correlative
data.
Both the European Community and the United States are now planning operational satellite
systems that will carry the ozone sounders required to extend the long term record already
produced by national research missions and the US NOAA operational system. NASA will also
continue to fly ozone chemistry instruments on their ADEOS and GCOM series of satellites.
However, despite the fact that the major space agencies have embarked on operational
atmospheric chemistry missions, no unified concurrent validation programme has been established
nor is there any assurance that the requisite ground-based infrastructure will be in place.
Satellite systems can only meet the requirements listed in Chapter 2 if they are supported
by correlative data of known quality and are continually challenged by reliable ground-based
observations and quantitative science. An on-going effort at NASA’s Goddard Space Flight Center
has shown that the series of satellite BUV instruments onboard NOAA operational and NASA
international research satellites can provide a continuous and accurate ozone data record of
climate quality, satisfying assessment issues extending from 1970 to the present. However, this
has only been accomplished by the comprehensive cross calibration and validation of satellite and
ground-based observations. This effort has also included the concurrent development of improved
radiative transfer models and the refinement of algorithms, and to a large degree has been
necessitated and guided by the intercomparisons. It is quite clear that satellite and ground-based
observations together form mutually supporting (and complementary) sources of information for
quantifying changes in the global distribution of ozone throughout the atmosphere.
Based on the experienced gained in these research satellite missions, an end-to-end
approach to calibration/validation, highlighting the need for a fully integrated global observing
system encompassing both ground and space-based, is clearly essential. This end-to-end
approach must include the satellite's internal calibration programme, post-launch calibration
(employing on-board systems), an external validation programme using highly controlled
correlative measurements, subsequent algorithm refinements and a scientific analysis of the data
to ensure consistency with the best understanding of atmospheric processes and conditions.
These steps form the basis of the recommendations from this chapter which are summarised in
Chapter 6.
Although validation programmes following this approach are planned for upcoming national
research missions, there are currently no calibration and validation programmes designed to
guarantee the overall integrity of global measurements over long periods of time and which meet
57
the objectives of IGOS. This is of particular importance given the existence of parallel streams of
the national missions (e.g. the European METOP and the US NPOESS ozone instruments). In
addition, a realistic possibility remains that gaps in one or both streams will arise and that the
systems may employ different wavelength ranges and techniques associated with significantly
different vertical resolutions. The ability of the atmospheric chemistry user community to combine
data sets from different remote sensing instruments will require that the calibration properties of
the individual systems are well understood and that the validation programmes be placed on a
common footing.
This chapter defines the calibration and validation process and describes briefly the various
systems available for validation. A set of principles and guidelines are listed to establish the basis
of an international calibration/validation programme. Finally an implementation strategy is
proposed.
5.2
Calibration and Validation Approach
Satellite sensors represent an enormous investment of intellectual and economic resources
but in return offer unique opportunities for observing the Earth, notably the ability to obtain
essentially global coverage with a small number of well-characterised instruments. However, to
satisfy the requirements listed in Chapter 2, of the scientific and the policymaking communities and
potential commercial users, the geophysical products derived from satellite sensors must be of
known quality and adequate for their intended use. The calibration and validation of satellite
sensors establishes the foundation on which the integrity of all these data is based:
Calibration involves the definition of a set of pre-launch and in-orbit operations (or
procedures) to determine the relationship between the quantities derived from the output of
the satellite instrument and the corresponding values available from a traceable
national/international standard.
Characterisation is the set of procedures used to quantitatively determine the sensor’s
response over the range of operating conditions experienced in orbit during its lifetime.
Validation is the objective assessment of the accuracy of the observables (radiances) and
retrievals of geophysical/atmospheric parameters from calibrated and well characterised
instruments over a range of geophysical conditions.
Experience has shown that several steps are required to produce validated data. These
steps are illustrated in Figure 5.1 beginning with the space-based measurement. These data are
converted to geophysical values, namely radiances commonly called Level 1 products, by means
of pre-launch calibration and on-board systems which correct for time dependent changes.
Radiance, Level 1 validation, can only be performed via comparisons conducted using instruments
with overlapping wavelengths. This has been done in the past and should be feasible for the
upcoming research and operational missions (i.e. ENVISAT, EOS-Aura, METOP and NPOESS)
though the need to observe the "same" air mass (time and location) will pose the usual problems.
Validation of Level 1 radiance data should be considered as a tool for isolating calibration
errors from algorithm errors. Algorithms, based on the best understanding of radiative transfer
properties of the atmosphere, convert radiances into estimates of atmospheric composition and
physical parameters (Level 2 products). These Level 2 products are validated by means of
correlative measurements and scientific analysis (to check for scientific consistency - this may
require further refinements of the algorithms). Once this is completed, the data may have to be
reprocessed to produce climate quality data sets. To realise the full potential of an instrument this
iteration normally occurs several times over the life time of the sensor.
Correlative measurements used for Level 2 validation come from many sources. These
include operational and dedicated surface-based measurements, dedicated airborne measurement
campaigns (aircraft and balloons), nationally and internationally co-ordinated field programmes
and sensors on other spacecraft measuring the same parameter. Also important are national and
58
international networks such as WMO-GAW, the NDSC and the World Climate Research
Programme (WCRP) Baseline Surface Radiation Network (BSRN).
However, it is important to remember that in many cases correlative measurements are not
the primary goal of the measuring network or programme, so their use in correlative measurement
programmes must recognise their limitations for that purpose. One key consideration is the need
to observe the "same" air mass (space and time).
59
The data quality of atmospheric chemical data products, derived from space-based
measurements, can be characterised by their accuracy, precision, resolution (temporal,
horizontal/vertical coverage) and compatibility. The definition of data quality for measurements
from national and international networks should follow the ISO-9000 guidelines (and ISO norms)
where it is established in terms of accuracy, precision, completeness, comparability and
representativity The ability to reliably assess and document the data quality of all correlative
measurements used in the validation process must be a major objective of both IGOS and this
Ozone Project. This ultimately requires the traceability of all geophysical parameters to
national/international primary standards, reference instruments or reference methods endorsed by
the international scientific community.
The current ground-based ozone observing network (total and profile) has limited spatial
coverage and thus cannot fully address the requirements of the satellite community for validation
and complementary measurements over a broad range of geophysical conditions. However,it
does provide a basis for a system addressing these requirements. For this a number of long term
monitoring sites, covering a range of geophysical conditions, must be selected from global
networks and designated as permanent satellite validation facilities. To be useful their long term
provision must be assured by the network operators, and for this the long term support of satellite
providers will be undoubtedly required.
5.3
Algorithms and Radiative Transfer
The retrieval of atmospheric constituents from measured radiances involves the use of
radiative transfer models which can only be as good as the knowledge of the processes involved.
This knowledge evolves continually so there is an ongoing need to refine radiative transfer models
in the light of increased knowledge, as well as to fine tune the retrieval algorithms to accommodate
instrument changes during its life in orbit. The algorithms, the radiative models and their
refinement all play an important role in validation as shown in Figure 5.1.
In many cases there is no unique solution to the retrieval problem so additional a priori
data, derived from other measurement systems (often ground-based), are required to further
constrain the analysis. Commonly (but not always) this is an iterative process, during which
measured and modelled radiances are closely matched and then geophysical parameters are
retrieved. These steps involve the use of both radiative transfer models and retrieval algorithms.
The BUV ozone data discussed above (Section 5.1) and the ongoing activity to validate
GOME data are examples of this process. Algorithm refinements incorporate instrument,
radiometric and wavelength calibration corrections. Radiative transfer model refinements follow
from improved understanding of the role of clouds and aerosols, of Raman scattering effects, etc.
The selection of a priori data, the improvement of radiative transfer models and the refinement of
algorithms are all essential components of validation and must be included as part of the IGOS
long term measurement strategy.
5.4
Ground-based Observations
Ground-based measurements have and will continue to play a vital role in an integrated
observing system as they are the primary source of data for validating Level 2 data products. It is
therefore essential to ensure that these systems are sustained to maintain continuity and data
quality. Intercomparisons between the various systems are essential to maintain the data quality of
the ground-based network. The natural extension for defining and documenting the
intercomparison process is to adopt and implement the International Standards Organisation’s ISO
9000 series standards for quality systems.
Given the fact that the global ozone monitoring system has become an essential foundation
for international decision-making, it is incumbent upon the various organisations to be able to
demonstrate the quality of the measurements at a level that can audited rather than to simply rely
60
on individual scientific reputation or competence. It is therefore logical to apply the ISO 9000
series principles and practices to this scientific field.
The following sections briefly describe the various ground-based ozone observing systems
and the way data quality is maintained. Table 5.1 lists routinely available ground-based systems in
place or planned. In addition, there are data available from the routine operational aircraft
observing programmes (Table 5.2) as well as from special calibration/validation campaigns such
as those being planned in support of ENVISAT and EOS-Aura.
Table 5.1: Current Long Term Global Ground Based Ozone Reference
Measurements
INSTRUMENT
NETWORK
DATA
STATUS
WMO-GAW and NDSC
Total Column
Ongoing
(part of GCOS)
WMO-GAW and NDSC
Total Column
Ongoing
(part of GCOS)
WMO-GAW and NDSC
Profile
Ongoing
(part of GCOS)
4
Selected Research
Sites
Tropospheric Profile
(< 12 km)
Research
(not yet incorporated in
networks)
4
NDSC
Stratospheric Profile
(> 12 km)
Ongoing
Selected WMO-GAW
and NDSC Stations
Total Column
Research
(not yet incorporated in
networks)
Selected NDSC
Stations
Total Column and
Profile
Research
SESAME
Total Column
Research
1
Dobson Spectrometer
2
Brewer Spectrometer
3
Ozone Sonde
Ozone Lidar
Ozone Lidar
5
FTIR
Microwave Radiometry
6
DOAS
Note - traceable standards or calibration facilities are as follows:
1.
2.
3.
4.
5.
6.
WMO-World Calibration Facility for Dobson, CMDL Boulder CO (Dobson No. 83) with
additional regional calibration facilities for the six WMO regions
WMO-World Calibration Facility for Brewer, MSC Toronto Canada
WMO-World Calibration/Instrument Characterisation Facility, Forschungszentrum Jülich
Germany. Traceable to NIST-Standard UV Photometer
Intercomparison with ozone sonde, which in turn is traceable to NIST Standard UV
Photometer
Fourier Transform Infrared Spectroscopy. No reference method, intercomparison with
Dobson/Brewer.
UV/Visible Differential Absorption Spectrometry of sunlight scattered by the atmosphere at
zenith.
61
Table 5.2: Routine Operational Aircraft Observing Programmes
PROGRAMME
CARIBIC
MOZAIC II
DESCRIPTION
SPECIES
SCALE/DOMAIN
AIRCRAFT
PERIOD
Instrumented
container
O3, CO, Aerosols
Europe/Indian Ocean
B767
1997-
Automatic
airborne devices
O3, H20
o
o
150 W - 50 E/80 N-25 S
A340
1996-99
B747
1995-96
NOXA
Automatic
airborne devices
NO, NO2, O3
o
o
o
o
15 N-70 N 90 W-120 E
TOP
Grab samples
CO2, CH4, CO,
N2O
o
o
o
38 N-38 S/145 E
B747
1993-98 / ?
MOZAIC III
Automatic
measurement
device
O3, H2O, CO, NOy
o
o
o
o
150 W-50 E/80 N-25 S
A340
1999-
NASA project
(planned)
Automatic
measurement
device
O3, CO, CHCl3;
CO2
Global
B747
Not yet
determined
5.4.1 Dobson Spectrophotometer
The ground-based network for the monitoring of the globe’s atmospheric ozone content is
primarily based on an international network of about 70 Dobson spectrophotometers, some of which
have been operational for many decades. Data collected over many years provide a crucial source
of quality information suitable for the detection of multi-decadal trends and variations in ozone
amounts.
International intercomparisons are now the established way of maintaining calibration within
the Dobson instrument network, i.e. the means by which the superior, independent calibration of the
World Standard Dobson Instrument (Dobson #83) is propagated throughout the network. In addition
to the actual field intercomparisons, laboratory assessments, internal adjustments and calibration
work are carried out in support of the intercomparison exercise.
The intercomparisons are organised by the WMO-GAW programme. The data quality of
these instruments has steadily improved and a sustainable precision of a few tenths of a percent
are now common. The quality of the intercomparisons is critical to the network’s quality and to the
accuracy with which ozone trends can be monitored. These must be continued. Data are available
from the WMO World Ozone and Ultraviolet Radiation Data Centre, hosted by the Meteorological
Service of the Canada (MSC) in Toronto.
5.4.2 Brewer Spectrometer
Brewer ozone spectrometers ("Brewers") were first deployed in the early 1980s and there
are now over 70 in operation. The reference for measurements of ozone made using these devices
is the Brewer Reference Triad, a group of three Brewers that are operated in Toronto most of the
time. They are calibrated independently at the Mauna Loa Observatory in Hawaii. One or other of
these Brewers has been taken to the Observatory eleven times since May 1983.
62
A key advantage of such a multiple-instrument standard reference (over one based on a
single instrument) is the possibility to make simultaneous measurements of the same quantity by all
three Brewers. An analysis of such measurements, spanning approximately 2200 days when all
three were in operation at Toronto, shows that:
•
•
the precision of the absolute calibration of these devices is about 0.3% (1-sigma);
the divergence in long term trends between the three Reference Brewers is less than 1% per
decade.
Toronto is the WMO-designated Centre for Brewer Calibration and MSC has undertaken to
maintain and consolidate the three Reference Brewers. The calibration of the other operational
Brewers is normally based on a few days of simultaneous on-site measurements made in
conjunction with a Travelling Standard Brewer, which is returned regularly to Toronto where it is
compared continually with the three Reference Brewers. Regular co-located observations are made
with Dobson spectrophotometer #77. Intercomparisons with the Brewers deployed in the networks
have been conducted over the past several years and these data are now being evaluated. Ozone
data from approximately 70 Brewers are available from the World Ozone and Ultraviolet Radiation
Data Centre.
5.4.3 Russian Filter Ozonometer M-124
The Russian network for observing total ozone column amounts consists of about 40
stations that are equipped with the M-124 filter ozonometers. Total ozone amounts are retrieved
o
o
from measurements made in direct sunlight at zenith angles of 20 -70 and from measurements
o
o
made in clear or cloudy conditions for zenith angles of 20 -85 . This allows the measurement of
o
ozone to be made at northern stations (16 Russian stations are located north of 60 ) under
practically all weather conditions.
All the M-124 ozonometers are calibrated against a reference instrument. For the Russian
network the Dobson spectrophotometer #108 has been designated as the standard and this
instrument is regularly compared with the WMO world standard Dobson spectrophotometer #83.
The results of three intercomparisons (i.e. Boulder 1988, Hradec Králové 1993, and Kalavrita 1997)
have shown that the measurement-scale drift of Dobson spectrophotometer # 108 does not exceed
0.5%.
Regular quality control, instrument calibration and verification are carried out under the
auspices of the Main Geophysical Observatory (St. Petersburg, Russia) and are based on intercomparisons and Langley analyses. Total measurement errors are less than 3% and estimated
uncertainties of mean monthly ozone values and ozone trends made by the M-124 ozonometers
approach those of other ozone stations employing Brewer and Dobson instruments
5.4.4 Ozone Sondes
Knowledge of long term trends of height resolved tropospheric and stratospheric ozone data
is limited by the lack of global coverage provided by the existing ozone sounding stations and the
questionable homogeneity of the data (WMO Scientific Assessment of Ozone Depletion, 1994).
In order to provide reliable data for IGOS and to optimise the use of existing networks for the
accurate measurement of tropospheric ozone profiles, it is absolutely essential to further improve
the quality of ozone sonde data. This can only be achieved by the intercalibration and the
intercomparison of existing ozone sonde types and agreement on procedures for data processing
and analysis (WMO Report No. 104, 1995). Recognising this need WMO-GAW has initiated
activities intended to ensure the realisation of quality assurance goals. These include the
establishment of a ”World Calibration Facility for Ozone Sondes” at the Research Centre in Jülich,
Germany where all major types of ozone sondes have already been compared and will continue to
be compared under controlled conditions.
63
The JOSIE (Jülich Ozone Sonde Intercomparison Experiment) 1996 provided valuable
information about the performance of the different ozone sonde types and the influence of operating
procedures applied by participating laboratories. JOSIE-96 also showed that it is essential to
validate ozone sondes on a routine basis. Ozone sondes have gone through various modifications
since they were first manufactured which adds uncertainty to trend analyses. Accuracy and
precision are altitude dependent and vary in magnitude according to sonde type, with the minimum
uncertainty in the middle stratosphere. It has been found that ECC-type (electro-chemical cell)
sondes typically achieve a precision of 3-5 % , while non-ECC types of sondes display a somewhat
lower precision (around 5-15 %). WMO-GAW now requires the routine testing of a representative
set of manufactured ozone sondes on a regular basis, following a standard operating procedure to
increase confidence in observed trends in the future.
5.4.5 Lidar
The differential absorption lidar (DIAL) system can be used to monitor vertical profiles of
atmospheric ozone with good vertical resolution. The method is particularly well suited for trend
studies as it is self-calibrated. However, DIAL measurements are subject to both statistical errors
(related to measurement signal-to-noise ratios) and to systematic errors arising from instrumental
limitations, differential backscatter and non-ozone differential extinction. This leads necessarily to
significantly different assessments of the accuracy and precision of DIAL systems at different levels
in the atmosphere. Lidar measurements require clear skies and this has to be taken into account in
selecting sites for long term studies.
At the present time there are about 12 stratospheric ozone lidar systems in operation
throughout the world which are used for long term monitoring as part of the Network for Detection of
Stratospheric Change (NDSC). The NDSC has developed a validation policy to ensure that the
results included in its archives are of a known quality and is as high as possible within the
constraints of measurement technology and retrieval theory at the time the data were taken and
analysed.
Several intercomparisons involving DIAL systems and other instruments have shown that the
region of best agreement among all the instruments (including SAGE II) is between 20 to 40 km. In
this region, single profile measurements agree to within 15% and average profiles based on specific
campaigns agree to within 10%. Systematic biases in this region are small. The DIAL
measurements are characterised by good precision and good vertical resolution especially in the
lower stratosphere. However, below 15 km altitude and in particular in the troposphere, the
accuracy and precision of lidar systems must be further assessed through additional
intercomparison experiments.
There is only a handful of tropospheric ozone lidars in world wide use and most operate in
the research mode. Under optimised conditions they provide, continuously, profiles of ozone, day
and night, with a vertical resolution of better than 1 km. However, they have not been rigorously
intercompared against independent measurement systems.
5.5
Validation of Trace Gases
The validation of measurements of trace gases listed in Annex B (Tables B.2) requires
special consideration as the concentrations of these gases are usually much lower than that of
ozone and their spatial and temporal variability are not as well understood. Some of these gases
can be measured by a variety of remote sensing techniques (occultation, thermal emission, etc.)
spanning different wavelength ranges and employing various algorithms. This variety affords many
approaches to validation as the various techniques can be intercompared. Validation strategies
must also take into account the fact that in these instances a trace gas will probably be observed
with different geometries and influenced by atmospheric variations. For some gases well calibrated
ground systems may not exist and, in these instances, validation will have to rely on the spacebased system intercomparisons.
64
Given the large differences between the trace gases to be validated and among the
instruments used, validations must be planned on a case-to-case basis. Knowledge of instrument
precision and atmospheric variability must be taken into account. For the trace gases listed in Annex
B (Tables B.2), instrument accuracies and precisions must be considered. It appears that the best
ground-based instruments usually achieve higher accuracy and precision than space-borne ones
(by a factor of between two to four). These factors define the number of coincident measurements
needed to obtain the desired accuracy of validation. For ground-based comparisons, coincidences
are less frequent and the separation distance must also be considered if the requisite statistical
significance is to be achieved. For some trace gases the validation depends on comparisons with
sophisticated ground-based instruments launched from a balloon. In these cases the bias errors as
listed in Annex B (Tables B.2) may never be achieved because of lack of precision and the limited
number of comparisons.
Validation (intercomparison) of parameters among satellite instruments is also feasible.
However, to achieve a given validity may require many more coincidences because of the lower
instrument precision. On the other hand, the typical number of coincidences available with low miss
distances and low miss times is high. A further advantage of such intercomparisons is that they can
be done in a "latitude-dependent" way. This is very desirable for measurements with global
coverage. It is clear that a freshly calibrated instrument, installed in orbit for a few weeks, can be a
very suitable intercomparison/validation tool. Ideally, intersatellite comparisons of trace gas data
should be supported by well calibrated ground-based systems.
Validation plans for ENVISAT and EOS-Aura are underway and will include special
campaigns (balloons, ships and aircrafts and the existing infrastructure (e.g. NDSC, GAW) with
some likely upgrades. Resources should be sustained such that these high quality data be
available for validation of future systems.
5.6
Scientific Analyses
The scientific analysis of satellite observations through the use of models has been shown to
be a powerful tool for validating satellite data although this is not validation in the true sense as
models do not necessarily predict the ”truth”. However, this process does allow objective human
interpretation of the data to ensure that they are reasonable and do not contain artifacts created by
the measurement process. All data sets should undergo such an analysis before being released to
the user (Figure 5.1). Two tools are available to support such an approach, namely chemistrytransport models and data assimilation (note they are not independent of each other).
5.6.1 Comparisons with Chemistry and Transport Models
Satellites provide valuable data for evaluating the performance of climate and atmospheric
chemistry models. However, models can also be used to help validate satellite data as chemistry
and transport models provide guidelines for values expected from observations. This approach is
applicable to both the determination of ozone trends and the observation of various trace species
associated with ozone chemistry. When the data sets disagree one or both are likely to be incorrect
(although there is always the possibility that both agree and are both incorrect). Combining models
and observations provides an opportunity to separate the effects of individual processes in models
exploiting the large-scale coverage offered by satellites.
Models can also be used to test the consistency of retrieval algorithms. Although groundbased measurements provide the primary validation data, they are limited in spatial and temporal
coverage. Regional and global models can be used to assess the consistency of an entire set of
observations from a satellite. This can be particularly useful for assessing algorithms used to derive
concentrations of species that are infrequently observed by satellites, and for cases where attempts
are made to increase vertical resolution. Discrepancies may point to problems with the retrieval
algorithms or possibly to aliasing due to the temporal coverage. However, they may also point to
model deficiencies so caution must be exercised though models have an important complementary
role to play in satellite validation.
65
5.6.2 Data Assimilation
Data assimilation is an essential tool in meteorology for deriving the optimal description of
the dynamical state of the atmosphere from various types of observations with different coverages
and uncertainties. In data assimilation, satellite observations (e.g., ozone) are fed into an
atmospheric model and are weighted with model-calculated ozone values in order to predict the
most likely state of the atmosphere. By extending the amount of data available to dynamical models
by data assimilation (which retains dynamical information on ozone), it is possible to obtain maps of,
for example, the distribution of ozone at any specific time, according to requirements. This is in
contrast to satellite global images from low Earth orbit which are based on interpolated data points
measured at different times.
Satellite instruments usually observe averages over a large area, whereas ground-based
measurements often represent local values which increases the uncertainty of intercomparisons.
Furthermore, ground-based measurements are often taken at different times and at geographical
locations than the satellite measurements. Comparisons with ground-based measurements can be
enhanced by employing data assimilation models to "intelligently" interpolate in space and time.
Cross comparison of data obtained from other satellite instruments can also be used for validation,
but suffer many of the same problems. Here again the use of data assimilation will improve the
statistics of the validations. Moreover, data assimilation offers the possibility of identifying ground
stations which deliver controversial data (by comparison with the analysed model fields) or
failures/problems in space-borne instruments.
Data assimilation models can also be used to compare satellite observations with predicted
tracer values (e.g. of ozone) based on previous observations made by the same satellite instrument.
Information on the differences between new observations and model forecasts provides insights into
the self-consistency of the data set provided by the satellite instrument, as well as on the quality of
the model. This implies that chemistry can aid dynamics and vice versa. In this manner, knowledge
of the ozone field can be significantly further improved by incorporating sonde, lidar, aeroplane,
surface and satellite measurements into a single harmonised and quality assured data set.
However, although operational data assimilation systems are currently available for use in NWP
(numerical weather prediction), only experimental ones exist for atmospheric chemistry.
5.7
Principles and Recommendations for Calibration and Validation
In order to implement a calibration and validation programme appropriate for IGOS, all the
steps described above and illustrated in Figure 5.1 must be considered. Thus, for the Ozone Project
it is strongly recommended that the following set of principles be adopted by national and
international organisations responsible for the development of space programmes and groundbased networks:
•
A "sense of community responsibility" must be fostered between the space agencies and
national/international agencies involved in the maintenance of ground-based networks. The
latter often lack the resources required to ensure the maintenance of data sets of
consistently high levels of quality or to provide the global coverage necessary to supplement
a truly global, space-based, ozone observing system; while the former may have formal
policies (or directions from their funding governments) that severely limit or prohibit their long
term support for ground-based systems.
•
A formal holistic validation programme must be developed and implemented which extends
over the entire life of each sensor/platform and across multiple instruments/ platforms. The
sense of "community responsibility" would be aided by recognising the ground-based
networks and the satellite observations as integral parts of the ozone observing system. For
this some carefully selected ground stations will have to be designated as permanent ground
"truthing" stations.
66
•
Procedures must be developed, implemented and properly documented to assure the
consistency of calibration and validation across related programmes, including ground-based
networks ("harmonisation"). Whenever appropriate, instrument outputs and derived
geophysical parameters must be tied to recognised traceable standards, reference
instruments and reference methods. Support for the infrastructure required to support
continual upgrades and to ensure the long term consistency of calibrations must be
assured.
•
The space agencies and instrument providers must commit themselves to long term cooperation with the scientific community to encourage the maximum use of the data provided
by the ozone observing system. Quantitative science is the ultimate and highest level of
quality assurance.
•
The long term and iterative nature of calibration/validation activities and algorithm
development must be recognised. Programmes should be developed in a way that assures
that validation results will be used in the algorithm improvement, which will then be tied to
requirements for subsequent reprocessing and the revalidation of data sets. The availability
of resources for these efforts must be assured.
•
Validation strategies (e.g., size, scope, nature of key ground networks) for space
programmes must be tailored specifically to the measurements at hand. The validation
process should involve the participation of appropriate members of the international scientific
community working together with the developers of specific instruments. Tools such as data
assimilation should be exploited.
5.8
Implementation Strategy
Implementing this set of principles represents a change in agency philosophy and a
significant expansion of validation activity as illustrated in Figure 5.1. On the other hand, they also
offer the potential for conserving significant resources through the co-ordination of calibration and
validation campaigns and programmes and the optimisation and sharing of facilities and expertise
(including the operational systems planned in Europe, Asia and the US).
A preliminary review of the launch schedule for satellites carrying ozone sensors and those
already in orbit (see Chapter 3) clearly shows a window of opportunity exists at this time for
implementing some or all of the recommendations listed in this report (Chapter 6). Most of the long
term ground-based facilities, frequently called upon to assist in the geophysical validation of spacebased systems already form an integral part of the global ozone observing system operated cost
operatively by WMO-GAW and NDSC. However, their continued operation well into the 21 century
is not assured and must be a matter of primary concern.
What is needed, then, is a pilot project with the specific goal of designing and formalising the
strategy for developing a co-ordinated approach to the construction and realisation of the globally
harmonised and mutually interdependent network of satellite and ground-based sensors, required to
assure the consistent provision of high quality ozone data sets (and associated observations) over a
long time period. This task could in principle be accomplished under the auspices of an IGOS
"ozone project".
67
68
6.
6.1
RECOMMENDATIONS
Introduction
The discovery of an annual spring time ozone depletion over Antarctica over a decade ago
provided evidence of a global change in the chemical composition of the atmosphere and, as a
result, new ground was broken in linking scientific observations and international policy action
(Montreal Protocol on Substances Depleting the Ozone Layer and ensuing amendments that
banned the production of ozone depleting substances and in particular the CFCs). The destruction
of ozone in the stratosphere and the global build-up of greenhouse gases are global environmental
threats and no one country acting alone can prevent the degradation to the continued well-being of
the planet’s ecosystems and the quality of life.
We are now faced increasingly with the need to assess the global consequences of
2
industrialisation for which reliable global environmental data are essential. Today, ground-based
and space-based sensors are used to verify not only that the Montreal Protocol is in fact working but
also, generally, to gather vital data on the changing global atmosphere and thus help establish a
solid scientific foundation for future policy debate and action. An integrated global observing system
(i.e. the combination and co-ordination of space-based and ground-based measurements) is
required as these sources of information complement and help validate each other. Both are
needed to ensure the provision of the data required to develop policies to protect the environment.
IGOS provides the basis for a strategic planning process linking research, long term
observations and operations. It entails matching requirements in the way of observations with
existing and planned capabilities and implies the existence of a forum in which national and
international agencies co-ordinate and tailor their own commitments to meet a global goal. However,
it also implies that countries which lack technological capabilities to actively participate in space
endeavours, or which have insufficient financial and human resources to establish a ground-based
component, be offered the opportunity to participate in IGOS, possibly calling upon a fund set up
specifically for such a purpose. From an IGOS perspective there are many areas of the globe that
are grossly under-sampled. This situation must be rectified by additional financial support. These
countries would then become stakeholders in (and contributors to) IGOS and be in a position to
participate actively in the process of global decision making (see Agenda 21 (Article 40) United
Nations Conference on Environment and Development, Rio de Janeiro, 1992).
Many of the elements of an integrated global observing system for ozone exist today.
National/international ozone monitoring and atmospheric chemistry research programmes have
already deployed several systems with additional missions scheduled for launch within the next ten
years. These systems include an array of space missions, ground-based networks and
measurements taken from airborne platforms (aircraft and balloons).
The primary purpose of these observations is to determine if the international protocols,
established to offset ozone depletion by regulating critical anthropogenic halogen-bearing gases,
are effective. These observations include measurements of total column and profile amounts of
ozone on a global basis. Also included are observations of atmospheric constituents important to
ozone chemistry, namely source, radical, reservoir and trace gases (and aerosol) whose
distributions and evolution must be understood in order to explain the observed changes in ozone
occurrence.
In addition to the ozone depletion issue, it is now recognised that global observations of
ozone and other atmospheric trace substances are important to further understand climate and air
quality. Systems developed in response to the environmental impact of ozone depletion are being
re-directed and/or adapted to take observations in the lower atmosphere to advance knowledge of
the impact of active constituents on the radiative and chemical properties of the lower atmosphere.
2
Note that generally in this report the use of the phrase "ground-based system" in the chapter implies airborne (balloon
and aircraft) operations as well as ground-based.
69
There is an overall requirement for accurate long term data sets so that observations can be
compared with models and their predictions. In some cases this implies the need for continuous
data sets (with overlaps assured when instruments are deployed in series) while for other
parameters only intermittent but regular, well calibrated measurements are required.
Ozone and atmospheric chemistry-related observations are being provided by a combination
of operational and research space-based systems and ground-based measurements. The
operational systems include the European GOME instrument on ERS-2 and METOP, and the US
OMPS instrument on NPOESS. In both cases commitments have made to continue making the
observations for at least two decades.
In addition, both Europe and the US will conduct at least one long term (~5 years)
atmospheric research mission, namely ENVISAT and EOS-Aura respectively. Japan, through its
ADEOS and GCOM missions will combine operational and research observations. Ground-based
systems that have been relied on for "ground truthing" these satellite sensors include those run
under the auspices of WMO-GAW and NDSC. However, the primary goal of these networks is to
document the physical and chemical changes of the atmosphere and to help unravel the causes of
the observed changes. The same is true of both ENVISAT and EOS-Aura.
The extent that these provisions, described in Chapter 3, meet the observational
requirements specified in Chapter 2, is discussed in Chapter 4. However, there remains the problem
of a lack of formal co-ordination among the space faring nations to optimise the deployed systems
and to assure data consistency/uniformity for international users. In addition, there must be formal
recognition and support for the international community which is providing the critical data (primarily
through ground-based measurements) for the independent calibration and validation of the spaceborne systems. Not only does this community provide supporting data for the satellite-based
systems, but it also collects crucial observations of ozone, climate and air quality not measurable
from space. These capabilities were also described in Chapter 3 and include measurements
conducted from the ground-based systems. The whole of Chapter 5 is devoted to an explanation of
the need for a long term calibration/ validation programme and an implementation plan that
recognises the crucial and complementary role of ground-based systems.
The following recommendations highlight the missing components of the future integrated
system as well as the deficiencies of existing systems which need to be improved in order to meet
the requirements of the science and user community for atmospheric observations. Only by
implementing these recommendations will the objectives of the Ozone Project and of IGOS itself be
met.
The recommendations described in this chapter are separated into four components:
•
•
•
•
The first addresses algorithm development and calibration procedures.
The second deals with the implementation of a globally integrated system.
The third considers the need for improved or additional measurements .
The fourth addresses the need for technical support for the funding agencies.
These recommendations draw heavily on the content of the previous chapters. These
chapters outline the scientific requirements for long term ozone and atmospheric chemistry
observations, describe past, existing and planned observing systems, and illustrate how these
requirements could be met by existing and planned observing systems.
The recommendations presented below attempt to identify those areas that remain deficient
and hence will hinder the collection of crucial environmental data on the state of the atmosphere of
the quality required to enable the state of the atmosphere to be properly monitored and changes
correctly interpreted, providing a basis for formulating environmental policy.
70
6.2
Algorithms and Calibration
6.2.1 Algorithms
The performance of inversion algorithms are based on the ability to predict observed
radiances and to retrieve the geophysical parameters from these radiances. For the planned
measurements, a great deal of algorithm development, supported by national agencies, is
underway. To some degree there is already international co-operation by the respective instrument
science teams in the areas of radiative transfer model development and comparisons.
•
International co-operation in the development of algorithms must continue with
an emphasis on pooling knowledge and establishing reference atmospheric
models and cross checking radiative transfer physics.
The performances of these models will determine the accuracies of the final data products.
Maximising accuracy will minimise systematic differences between observing systems involving
various measurement techniques and approaches.
•
Algorithms for many common observing systems, such as those exploiting
backscatter (GOME, OMPS) and thermal emission (IMG, MIPAS, TES), are
generally not identical. Therefore, intercomparisons must be encouraged if
maximum accuracy is to be achieved.
It is possible that a common algorithm could evolve for all systems exploiting the same
measurement technique. Here it will be essential to ensure that a consistent spectroscopy is used
when considering instruments covering the same spectral ranges.
•
To ensure the availability of such spectra the quality of existing spectra must be
reviewed and further laboratory measurements instigated to correct deficiencies
6.2.2 Calibration
The calibration of both space- and ground-based systems provide key data on instrument
characteristics, essential for the transfer of instrument output to radiances and to the realisation of
the high measurement accuracies needed to minimise systematic differences between observing
systems (essential if these data are to be of value to the user community). The techniques
employed rely on national standards and require careful implementation.
•
Scientists who maintain and improve national calibration standards must be
involved when these standards are applied to calibrating remote sensing
instruments.
The refinement of calibration techniques by the instrument providers is already underway but
needs to be consolidated.
•
Calibration techniques must be intercompared and, where applicable, cross
calibration must be encouraged.
•
The user must be involved in the analysis of calibration data. For this full
documentation and description of procedures will be essential.
The ground-based measurement systems (i.e. existing networks plus supplementary stations)
must be regularly challenged through calibrations and intercomparisons - an absolute pre-requisite
for reliable data gathering. For this purpose, WMO-GAW has either established World Calibration
Facilities (WCFs) or else it has provided reference instruments, though not for all measurement
parameters and with no assurance of long term continuity. All ground-based measurements must
71
ultimately be traceable to a world standard (calibration gases or reference instruments) and must
demonstrably meet the data quality objectives set by IGOS.
•
Additional support is needed to upgrade and maintain a comprehensive and
rigorous quality assurance programme for ground-based components.
•
Traceability must be established for all parameters and measures implemented to
remedy omissions.
For the latter, as an interim solution, instrument intercomparisons would be an acceptable
procedure for initiating the global harmonisation of data sets.
6.3
Implementation
The implementation of an integrated observing system has many facets including
deployment, instrument operations, data acquisition, data production and archiving and, last but not
least, data validation. For each of these facets the needs of the international user must be
considered recognising however that national agencies, that provide the resources, may have other
priorities. Nevertheless, it is important to note that it is very likely that significant cost efficiencies will
be achieved through international co-operation.
A further problem arises because in many instances the measurement types and their
platforms have already been selected. This limits flexibility as it means that it is feasible to consider
only a limited set of options in formulating an integrated strategy for deployment; only certain areas
remain open for further consideration and international co-operation. These include algorithm
development, their implementation, pre-launch instrument calibration and, most importantly, a
commitment to sensor validation over its life time on the basis of ground-based and airborne
observations.
6.3.1 Coverage
As discussed in Chapter 3, the deployment of the space-borne component of the global
system is already underway. Although these systems have been designed to meet individual
national priorities, they are based on requirements that have fairly wide international scientific
support. However, they do not yet meet the full requirements.
Ground-based systems must not only meet the challenge of supporting the space-based
component through well co-ordinated validation activities, but they must also expand their activities
into geographic areas that are now grossly under sampled.
•
Mechanisms must be identified that will allow countries in under sampled
geographic areas to become actively involved in IGOS and the Ozone Project
under the umbrella of WMO-GAW and/or NDSC.
•
The geographical distribution of ground-based systems (for nearly every
atmospheric constituent) falls short of requirements and must be expanded,
notably in the tropics and in the Southern Hemisphere.
In parallel, in partial support of the recommendation, it is important to ensure that scientists
and engineers in developing countries are fully involved in the Ozone Project.
The various instruments that are deployed in space will have different capabilities with regard
to field-of-view and geographical and vertical coverage. This will be particularly true for instruments
flying in low and non-low Earth orbits such as geostationary. Another point to note is that METOP,
NPOESS, and GCOM, though all in low Earth orbit, will have different (or even varying) equator
crossing times.
72
•
The operation of deployed instruments must be co-ordinated to ensure that the
coverage required to meet the requirements particularly in the case of the failure
of one of the observing systems.
•
Options must be considered which will facilitate the synergistic use of data from
different measurement systems such as space-borne systems operating in
different orbits (i.e. LEO, GEO and L1).
6.3.2 Operations
The challenge of securing and maintaining financial commitments for upgrading and/or
expanding existing ground-based networks cannot be met by WMO-GAW and NDSC alone; neither
of them has sufficient resources even to meet current commitments and needs. WMO-GAW relies
largely on the ability of Membership countries to support stations within their boundaries, while
scientists contributing to NDSC must secure their own support through proposals to funding
agencies. Clearly this situation is not satisfactory and demands a solution. One solution is to
establish a special fund.
•
The possibility of establishing a fund must be considered to provide support (on
the basis of demonstrated need and capability) to the ground-based component to
ensure its uninterrupted long term operation and also to expand the network into
regions of the globe that are currently under sampled.
This activity could also be supported by individual bilateral agreements.
6.3.3 Data Production and Archiving
The justification for the deployment of the various space and ground-based systems is to
collect data that is easily accessible and useable by the user. Various agencies have devoted
significant resources to support the provision of data to users. Data formats are being devised and
harmonised, archives built and outreach activities initiated to ensure that the user is aware of data
characteristics and validity. However, this needs to be consolidated:
•
To facilitate data usage providers must consider developing data products that
have common formats, descriptions and accessibility routines.
•
As far as is practicable common units must be employed to describe co-ordinates
(height and location) and the numerical values of measured quantities.
•
Archived data bases must have common formats with pointers available to
indicate locations and how to access to data from the various archives.
•
Resources must be made available to reprocess data sets in the light of validation
exercises and to ensure that the highest quality data sets are available to the user
community.
These recommendations are applicable to both space- and ground-based systems.
6.3.4 Validation
The calibration and validation of environmental data sets is fundamental to the realisation of
the long term objectives of the Ozone Project and the use of the data. Therefore, space faring
nations and nations participating in global atmospheric research, have allocated significant
resources to support calibration and validation. However, currently there is no specific programme
designed to guarantee the overall integrity of global measurements over the long term and required
to meet the objectives of the Ozone Project.
73
Chapter 5 deals with this issue in some detail considering an end-to-end approach for
calibration and validation which includes pre-and post-launch calibration, the refinement of
algorithms and scientific analysis (exploiting best understanding of the atmosphere) necessary to
insure consistency. A comprehensive and controlled correlatives measurement programme using
ground-based (ground, balloon, and aircraft) observations forms the basis of the ozone atmospheric
chemistry validation programme. This implies, however, that ground-based observations provide
quality assured data sets and that consequently the recommendations in Section 6.2.1. have been
implemented, at least for parameters critical for satellite validation.
Chapter 4 specifies the deficiences in the existing provisions which are also addressed in
Chapter 5. They include subset recommendations specific to calibration/validation. These may be
summarised as follows:
6.4
•
A holistic validation programme must be developed and implemented extending
over the entire life time of each observing system and across observing systems.
The space- and ground-based systems (including algorithms, spectroscopy, etc.)
must be considered as integral parts of the overall observing system.
•
The long term and iterative nature of calibration/validation and algorithm
development must be recognised. Resources must be made available to ensure
that validation results are used for algorithm improvement, which are then tied to
requirements for the subsequent reprocessing and the revalidation of data sets.
•
A carefully selected subset of WMO-GAW and NDSC stations must be designated
as permanent satellite validation stations and fully integrated into the planning
and execution phases of satellite validation activities. They would be the primary
stations for the long term validation of satellite sensors as called for in this
report.
•
Data assimilation facilities must be further developed and made available for
validation purposes. Associated with this the possibility of relaxing resolution
(spatial and temporal) requirements could be considered.
•
The geographical distribution of ground-based systems (for nearly every
atmospheric constituent) falls short of requirements and must be expanded,
notably in the tropics and in the Southern Hemisphere, to demonstrate the ability
of space-borne systems to retrieve accurate data under all observing conditions.
Recommendations for Additional Space-Borne Measurements
Chapter 4 compares current provisions with the requirements. Decisions on the deployment
of these systems were based on a combination of user requirements, national priorities and
available resources. It is clear that proposed systems, assuming funding is stable, come a long way
to meeting the requirements. However, there are some significant deficiencies.
ENVISAT, EOS-Aura and the ILAS-2/GCOM missions together should meet many of the
requirements outlined in Chapter 2. However, these are non-operational missions (though some
ENVISAT products will be produced operationally in near real time) which are expected to end
before the end of this decade, and there are no firm plans for follow-on missions of a similar kind.
Space faring nations may be planning follow-on missions but it is not clear that these will also meet
the requirements listed in Chapter 2:
74
•
There is a need to enhance the operational provision of data. GOME-2 and OMPS
flying on METOP and NPOESS will only measure a subset of the requirements.
These or new systems must include:
•
•
•
•
Reliable measurements of lower and upper tropospheric ozone at urban scale
resolution required for a variety of environmental purposes;
Profile information for NO, NO2, CH4 in the troposphere for air quality and
climate research;
Upper tropospheric/lower stratospheric measurements of BrO and ClO
(though SAGE III may produce some BrO profile information in the lower
stratosphere).
Non low Earth Orbits must be considered for the detailed global observation of air
quality as they will permit the continuous monitoring of plumes and the
observation of high temporal and diurnal variations. TRIANA will be exploring
this vantage point.
For tropospheric observations, the ground-based networks have to play a dominant role in
ensuring representative spatial and temporal coverage for all important parameters. To assume this
role requires that recommendations regarding network expansion, rigorous quality assurance and
long term commitment of this component be fully implemented.
6.5
Advisory Body for the Ozone Project
The formulation and realisation of an integrated global observing strategy for ozone
represents an enormous challenge for scientists, engineers, managers and politicians. Success will
only be achieved through the involvement of many different communities ranging from atmospheric
modellers, laboratory spectroscopists and those involved in technology development, system
operations and data analysis together with scientific users and policy makers. Observations of the
composition of the atmosphere involves an extremely diverse set of instruments operating under
varying conditions.
In addition, even as the environment changes because of long term environmental cycles
and anthropogenic forcing, the ozone/atmospheric chemistry discipline continues to evolve with
advances in knowledge . Thus, requirements (and hence subsequent strategy) can also be
expected to evolve with time.
•
It is therefore recommended that an international advisory body be established to
provide overall direction and to ensure the implementation of specific sets of
recommendations, taking due note of the philosophies and time constraints
outlined in this report.
The advisory body would be best organised under the auspices of bodies such as WMO and
CEOS. It must have the capability to address the following topics:
•
The identification of missions required to meet requirements not covered by the
operational (METOP and NPOESS) systems.
•
The refinement of requirements notably in the light of emerging interests in air
quality and advances in understanding of chemical interaction and climate
forcing.
•
The further modelling activities needed to improve the scientific basis for
predictions. Data type requirements must be specified.
75
•
The organisation of data providers to ensure the best and most cost effective use
of resources including space- and ground-based systems.
A calibration/validation advisory group is also needed to consider global approaches to the
provision of high quality data from the space- and ground-based observing networks. This group
should also consider global strategies for calibration/validation activities (including special
campaigns).
6.6
Concluding Remarks
There is a definite sense of urgency in the need for the international community to commit to
and fully establish strategy dedicated to monitoring of ozone and atmospheric chemistry and to
swiftly implement the recommendations made in this report. Critical gaps in observing systems must
be corrected as soon as possible. Anticipated trends in population growth and corresponding
increases in demand for energy, food and other natural resources, imply the need for prudent
decisions to be made in order to minimise the impact on the environment, while maintaining durable
development.
Reliable answers are needed to the question: “What is changing and why?” There is also a
more practical incentive for swift action: Several satellite systems are scheduled for launch during
this decade all requiring extensive ground validation and co-ordination to comply with the above
recommendations. A considerable cost savings is anticipated if a fully functional Ozone Project
supporting IGOS is established which could actually off-set some, if not all, of the financial burden
resulting from the implementation of recommendations put forth in this report.
76
ANNEX A
LIST OF SCIENTISTS AND EXPERTS CONSULTED
77
78
List of Scientists and Experts Consulted
The views of three general classes of scientists and experts were sought in drafting the
Report on the Ozone Project, namely:
A)
User Body Representatives
EC
EOCU
GCOS
IGAC
IGBP
IOC
IPCC
NDSC
A. Ghazi (EC, Brussels, Belgium)
N. Harris (European Ozone Research Coordinating Unit, Cambridge, UK)
D. Whelpdale (Atmospheric Environment Service, Downsview, Ontario, CDN)
G. Brasseur (Service d’Aéronomie du CNRS, Verrières-le-Buisson, F)
C. Rapley (British Antarctic Survey, Cambridge, UK)
R. Hudson (University of Maryland, College Park, USA)
N. Harris (European Ozone Research Coordinating Unit, Cambridge, UK)
R. Zander (Institut d’Astrophysique et de Geophysique de l’Université de Liege, B)
SPARC
UNEP
WCRP
WMO
M. Geller (State University of New York at Stony Brook, NY, USA)
G. Mégie (Service d’Aéronomie du CNRS, Paris, F)
H. Grassl (WMO, Geneva, CH)
J. Gille (National Center for Astrophysic Research, Boulder, CO, USA) and V. Mohnen
(Atmospheric Research Science Centre, Albany, USA)
B)
Space Agency Representatives
USA (NASA)
Europe (ESA)
Canada (CSA)
France (CNES)
Europe (Eumetsat)
Germany (DLR)
Italy (ASI)
Japan (NASDA)
UK (BNSC)
USA (NOAA)
C)
J. Kaye (co-lead; NASA Headquarters, Washington DC, USA)
C. Readings (co-lead; ESA–ESTEC, Noordwijk, NL)
R. Hum
N. Papineau (CNES Headquarters, Paris, F)
A. Ratier (Eumetsat, Darmstadt, D)
M. Bittner (DLR, Oberpfaffenhofen, D)
F. Svelto (ASI, Rome, I)
T. Ogawa (NASDA, Tokyo, J)
N. Harris (European Ozone Research Coordinating Unit, Cambridge, UK)
L. Flynn (NOAA-NESDIS, Camp Springs, MD, USA)
Experts and Specialists Consulted
D. Albritton (NOAA Aeronomy Laboratory, Boulder, Colorado USA)
P. Bernath (University of Waterloo, Ontario, Canada)
R. Bevilacqua (US Navel Research Laboratory, Washington DC, USA)
J. Burrows (University of Bremen, Bremen, Germany)
P. Canziani (University of Buenos Aires, Buenos Aires, Argentina)
K. Chance (Smithsonian Astrophysical Observatory, Cambridge, Massachussets, USA)
M-L. Chanin (Service d'Aéronomie du CNRS, Verrières-le-Buisson, France)
W.F.J. Evans (Trent University, Ontario, Canada)
J. Fishman (NASA Langley Research Center, Hampton, Virginia, USA)
G. Golitsyn (Russian Academy of Sciences, Moscow, Russia)
M. Gunson (Jet Propulsion Laboratory, Pasadena, California, USA)
F. Hasebe (Ibaraki University, Mito, Japan)
79
E. Hilsenrath (NASA GSFC, Greenbelt, Maryland, USA)
I. Isaksen (University of Oslo, Norway)
J. Langen (ESA–ESTEC, Noordwijk, NL)
M. Lawrence (Max Planck Institut für Chemie, Mainz, Germany)
H. Kelder (KNMI, de Bilt, & Technical University, Eindhoven, The Netherlands)
V. Khattatov (Central Aerological Observatory, Moscow, Russia)
V. Kirchhoff (INPE, Cachoeira Paulista, Brazil)
J. Langen (ESA–ESTEC, Noordwijk, The Netherlands)
G. Leppelmeier (Finnish Meteorological Institute, Helsinki, Finland)
J. Logan (Harvard University, Cambridge, Massachussets, USA)
H. Masuko (Communications Research Laboratory, Tokyo, Japan)
M. McCormick (NASA Langley Research Center, Hampton, Virginia, USA)
A. Miller (NOAA NWS, Camp Springs, Maryland, USA)
J. Miller (WMO, Geneva, Switzerland)
D. Offermann (University of Wuppertal, Germany)
S. Oltmans (NOAA/CMDL, Boulder, Colorado, USA)
R. Randel (NCAR, Bolder, USA)
W. Planet (NOAA-NESDIS, Camp Springs, MD, USA)
U. Platt (University of Heidelberg, Germany)
M. Schoeberl (NASA GSFC, Greenbelt, Maryland, USA)
P. Simon (Belgian Institute for Space Aeronomy, Brussels, Belgium)
Y. Timofeyev (St. Petersburg State University, Russia)
D. Wardle (Meteorological Service of Canada, Downsview, Canada)
80
ANNEX B
TABLES OF USER REQUIREMENTS
81
82
Tables of User Requirements
This Annex contains a set of tables which summarise all the user requirements discussed in
Chapter 2 (those for ozone are reproduced here for the convenience of the reader). These
requirements are derived from those included in the "User's Requirements Data Base" prepared by
the World Meteorological Organization and the report of the ad-hoc Global Climate Observing
System (GCOS) Atmospheric Chemistry Panel meeting (Toronto, Canada, May 23, 1997). They
were reviewed by participants at the inaugural meeting for the CEOS Ozone Pilot Project held in
July, 1997 in Tokyo, Japan and during the Ozone Project Consultative Workshop held in May, 1999
in Geneva, Switzerland. The views of SPARC and IGAC have also had a strong bearing on the
compilation of the requirements.
Two levels of requirements have been derived for each parameter, namely:
•
•
The "target" set of requirements - defined as the set of requirements that satisfy the needs
of most (if not all) of the user community.
The "threshold" set of requirement – defined as the minimum set of requirements which
satisfy the needs of at least one set of users.
In generating these tables great reliance has been placed on "quantitative science" i.e. on
measured concentrations, on published trend assessments and on known concentration differences
in the vertical and horizontal distribution of the stated parameters. The target values are derived
from user observation criteria (as used in atmospheric chemistry, trend analyses, etc...) and
substantiated by "local" observations which exploit the best available technology. This means that,
based on anticipated performance and target and threshold values, the benefits associated with the
deployment of specific systems will be identifiable.
Since requirements vary with height, it is logical (albeit a little controversial) to link and
thereby generalise them to some broad pressure/altitude regimes, notably:
• Total Column
• Lower Troposphere
• Upper Troposphere
• Lower Stratosphere
• Upper Stratosphere and Mesosphere
0 to 5 km
5 km to Tropopause
Tropopause to 30 km
> 30 km
Within these altitude ranges, the extreme variability with height of some of the parameters
has made it necessary in some cases to subdivide the levels further i.e. the use of “Tropospheric
Column” as well as to “Total Column” to accommodate all user requirements.
The tables summarise the needs for data on surface level concentrations, total column
amounts and vertical profiles using the altitude regions (where applicable) defined above.
Requirements are less well established in the upper stratosphere and mesosphere than for other
parts of the atmosphere:
•
Table B.1 details requirements for O3.(reproduction of Table 2.1)
•
Tables B.2 detail the requirements for the "source gases" listed in Table 1.1 (i.e. water
vapour (H2O), nitrous oxide (N2O), methane (CH4), carbon monoxide (CO) and carbon
dioxide (CO2)).
•
Tables B.3 detail the requirements for the "reservoir species" listed in Table 1.1 (i.e.
hydrogen chloride (HCl); nitric acid (HNO3).
83
•
Tables B.4 detail the requirements for the "free radicals" listed in Table 1.1 (i.e. bromine
oxide (BrO), chlorine monoxide (ClO), nitrogen dioxide (NO2) and nitric oxide (NO)).
•
Tables B.5 detail the requirements for temperature and wind (for water vapour see Table
B.2a).
•
Tables B.6 detail the requirements for aerosols and polar stratospheric clouds.
It should be noted that in Table B.2e the target values for CO2 in the troposphere are set to
meet the most stringent requirements for trend detection (currently 0.36 ppm/year and only
detectable through surface-based observations). The target values for horizontal resolution (10 km)
are set to allow detection of "hot spots" of CO2 emission from satellites (total column). Lower
stratospheric CO2 measurements are important for obtaining the seasonal cycle of CO2 which has
an amplitude of about 4 ppm in the tropics (transport process studies). Upper stratospheric CO2
measurements reflect only the annual increase. In addition, height resolved stratospheric CO2
measurements are used for deriving temperature.
84
Table B.1: Target and threshold requirements for ozone (O3 ) - greenhouse gas, ultraviolet shield and air pollutant. Target
requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy the needs of
at least one user group.
Region
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Temporal Res.
(observing cycle; hrs)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Lower
Troposphere
250
<10*
5
0.5
20%
or 4 ppb
3 % or
1 ppb
30%
or 6 ppb
5% or
2 ppb
168
3
0.5
Upper
Troposphere
250
50
5
0.5
20%
or 4 ppb
3 % or
1 ppb
30%
or 6 ppb
5% or
2 ppb
168
3
0.5
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
250
50
3
0.5
15%
or 100 ppb
3% or
20 ppb
20%
or 150 ppb
5% or
40 ppb
168
3
0.3
250
50
6
0.5
15%
or 75 ppb
3% or
20 ppb
20%
or 100 ppb
5% or
30 ppb
48
3
0.3
Total Column
100
10
-
-
5%
or 6 DU
1% or
3 DU
5% or
6 DU
1% or
3 DU
24
6
0.1
Total Column
(Troposphere)
100
10
-
-
15% or 6
DU
5% or
3 DU
15% or
6 DU
5% or
3 DU
24
6
0.5
Note * - Lower range due to air quality user/process study requirements.
85
Target
Trend Detection
(with continuity)
% per year
Table B.2a: Target and threshold requirements for water vapour (H2O) - climate gas and OH-precursor (specific humidity:
ratio of mass of water vapour to the mass of moist air, units g / kg.). Target requirements for bias error and RMS error are
consistent with trend requirements. Threshold requirements satisfy the needs of at least one user group.
Region
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
(by mass)
-3
10 g/kg
Threshold
Target
Threshold
Target
Threshold
Lower
Troposphere
500*
10*
2*
0.1*
1*
Upper
Troposphere
250
50
3
0.5
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
1)
250
50
3
250
50
Total Column
2)
Stratosphere
250
Total Column
(Troposphere)
500*
Bias Error
(by mass)
-3
10 gkg
Trend
Detection
(% per year)
Threshold
Target
Threshold
0.25*
n/s*
n/s*
12*
0.5*
n/s*
3
0.5
3
0.5
168
6
1
0.5
1
0.3
1
0.3
168
6
1
3
0.5
1.5
0.4
1.5
0.4
168
6
1
50
-
-
1
0.3
1
0.3
168
6
1
10*
-
-
500g/m *
n/s*
n/s*
12*
0.5*
n/s*
2
Target
Temporal Resolution
(observing cycle; hrs)
1000g/m
*
2
Note * - Requirement for lower tropospheric water vapor comes from IGOS Upper Air Group (n/s – not specified)
1)
Note - High resolution (<100 m) required near the hygropause.
2
Note ) - Based on average mixing ratio for the layer.
3)
Note - Estimated currend trend <35 ppb/year in lower stratosphere.
4)
Note - Estimated current trend 70 to 120 ppb/year.
86
Target
3)
4)
Table B.2b: Target and threshold requirements for nitrous oxide (N2O ) - greenhouse gas and stratospheric chemistry (source
of NO). Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements
satisfy the needs of at least one user group.
Region
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
(by volume)
Threshold
Target
Threshold
Target
Threshold
Target
Lower
Troposphere
250
100
4
1
5 % or
15 ppb
0.5 % or
1.5 ppb
Upper
Troposphere
250
100
4
1
5 % or
15 ppb
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
250
100
3
1
250
100
3
Total Column
250
100
Total Column
(Troposphere)
250
100
Bias Error
(by volume)
Threshold
Temporal Resolution
(observing cycle;
days)
Trend
Detection
(% per year)*
Target
Threshold
10% or
30 ppb
1 % or
3 ppb
7
0.5
0.5
0.5 % or
1.5 ppb
10% or
30 ppb
1 % or
3 ppb
7
0.5
0.5
10% or
20 ppb
2 % or 5
ppb
20% or
40 ppb
4 % or
10 ppb
7
0.5
0.5
1
20% or
40 ppb
5 % or
10 ppb
30% or
50 ppb
10% or
20 ppb
7
0.5
0.5
-
-
5%
1%
10 %
2%
7
0.5
0.5
-
-
5%
5%
10 %
2%
7
0.5
0.5
Note* - Tropospheric concentration 300 to 330 ppb and current annual trend 0.6 ppb/year (0.2 %/year).
87
Target
Table B.2c: Target and threshold requirements for methane (CH4) - greenhouse gas, stratospheric source of H2O and Atmospheric
Chemistry. Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy
the needs of at least one user group.
Region
Horizontal
Resolution (km)
Threshold
Target
Lower
Troposphere
250
10
Upper
Troposphere
250
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Temporal Resolution
(observing cycle;
days)
Trend
Detection
2)
(% per year)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
4
2
10 % or
100 ppb
1 % or
15 ppb
20% or
200 ppb
2 % or
30 ppb
7
0.5
0.5
50
4
2
10 % or
100 ppb
1 % or
15 ppb
20% or
200 ppb
2 % or
30 ppb
7
0.5
0.5
250
50
3
1
10 % or
100 ppb
2 % or
25 ppb
30% or
200 ppb
5 % or
50 ppb
7
0.5
0.5
250
50
3
1
10 % or
100 ppb
2 % or
25 ppb
30% or
200 ppb
5 % or
50 ppb
7
0.5
0.5
Total Column
250
50
-
-
5%
1%
10 %
2%
7
0.5
0.5
Total Column
(Troposphere)
250
50
-
-
5%
1%
10 %
2%
7
0.5
0.5
1)
1)
Note - To detect source regions.
2)
Note - Tropospheric concentration 1.7 to 1.8 ppm, inter-hemispheric difference 150 ppb and current trend 5-10 ppb/year.
88
Target
Table B.2d: Target and threshold requirements for carbon monoxide (CO) - precursor, atmospheric chemistry and air quality.
Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy the
needs of at least one user group.
Horizontal
Resolution (km)
Region
Threshold
Target
Lower
3)
Troposphere
250
10
Upper
3)
Troposphere
250
Lower
Stratosphere
Total Column
4)
Total Column
(Troposphere)
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Temporal Resolution
(observing cycle; hrs)
Trend
Detection
(% per year)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
1)
2
0.5
20% or
30 ppb
1 % or
2 ppb
40% or
60 ppb
2 % or
4 ppb
24
6
2
10
1)
4
1
20% or
30 ppb
1 % or
2 ppb
40% or
60 ppb
2 % or
4 ppb
24
6
2
250
50
5
2
15 % or
12 ppb
5 % or
2 ppb
25 % or
20 ppb
10 %
or
5 ppb
24
6
n.r
250
10
-
-
10 %
1%
20 %
2%
24
6
2
250
10
-
-
20 %
2%
40 %
5%
24
6
2
1)
Note - Lower range due to air quality user/process study requirements
2)
Note - Based on current tropospheric trend of minus <2.3 ppb / year.
3)
Note - N.H. background range in LT:100-240 ppb; S.H. in LT: 30-75 ppb; in LS 20 to 70 ppb in both Hemispheres.
4)
14
-2
Note -Total column density range : 0.5 to 3*10 molecules m .
5)
Note - Not relevant.
89
Target
2)
5)
Table B.2e: Target and threshold requirements for carbon dioxide (CO2) - precursor, atmospheric chemistry and air quality.
Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy the
needs of at least one user group.
Region
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
(by volume)
Target
Bias Error
(by volume)
Target
Threshold
Target
Threshold
Lower
Troposphere
5000
10
2
0.5
1 ppm
0.02 ppm
2 ppm
0.1 ppm
2 per
month
0.5
0.05
Upper
Troposphere
5000
10
5
1
2 ppm
0.04 ppm
4 ppm
0.2 ppm
2 per
month
0.5
n.r
Lower
Stratosphere
5000
250
5
1
2 ppm
0.5 ppm
5 ppm
1 ppm
2 per
month
0.5
n.r
Total Column
5000
250
25
5
2 ppm
0.5 ppm
5 ppm
1 ppm
2 per
month
0.5
n.r
Total Column
(Troposphere)
5000
10
n.r
n.r
10%
0.5%
20%
1%
2 per
month
0.5
0.15
90
Target
Threshold
Trend
Detection
(% per year)
Threshold
Note n.r. - Not relevant
Threshold
Temporal Resolution
(observing cycle;
days)
Target
Table B.3a: Target and threshold requirements for hydrogen chloride (HCl) - controller of ozone, heterogeneous chemistry.
Horizontal
Resolution (km)
Region
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Target
Threshold
Target
Threshold
Lower
Troposphere
250
50
5
1
20 % or
0.5 ppb
10 % or
0.1 ppb
40 % or
3)
1 ppb
15 % or
0.1ppb
24
6
n.r.
Upper
Troposphere
250
50
5
1
40 % or
0.3 ppb
10 % or
0.05ppb
40 % or
0.5 ppb
15 % or
0.05
ppb
24
6
n.r.
1)
250
50
4
1
20 % or
0.5 ppb
3 % or
0,2 ppb
30 % or
1 ppb
5 % or
0.3 ppb
24
6
1
250
50
4
1
20 % or 0.7
ppb
5 % or
0.3 ppb
40 % or
1 ppb
10 % or
0.5 ppb
24
6
1
250
50
-
-
15 %
3%
20 %
5%
24
6
1
n.r.
n.r.
-
-
-
-
-
-
n.r.
n.r.
n.r.
Total Column
4)
Total Column
(Troposphere)
1)
Threshold
Target
Trend
Detection
2)
(% per year)
Threshold
Lower
Stratosphere
Upper
1)
Stratosphere
/Mesosphere
Target
Temporal
Resolution
(observing cycle;
hours)
Threshold
Target
Note - Concentration Range: 0.3 at 150 hPa to 4 ppb at 1 hPa (less in Troposphere, 100 to 300 ppt over remote oceans).
2)
Note - Estimated trend for stratospheric HCl loading: < 3 % / year).
3)
Note - Near urban regions.
4)
11
2
Note - Estimated column abundance ca 4 * 10 molec./ m
Note n.r.- Not requested/not relevant.
91
Table B.3b: Target and threshold requirements for nitric acid (HNO3) - precursor and controller. Target requirements for bias
error and RMS error are consistent with trend requirements. Threshold requirements satisfy the needs of at least one
user group.
Region
Horizontal
Resolution (km)
Threshold
Target
Lower
Troposphere
250
10
Upper
Troposphere
250
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Temporal Resolution
(observing cycle; hrs)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
1)
3
0.5
40% or
2)
1 ppb
10% or
0.1 ppb
50% or
2)
2 ppb
15% or
0.2 ppb
24
6
10
1)
3
0.5
40% or 200
ppt
10% or
75 ppt
50% or
500 ppt
15% or
100
ppt
24
6
250
50
4
0.5
30%
or 1 ppb
10% or
40 ppt
40% or
2 ppb
15% or
250 ppt
24
6
250
50
4
0.5
30% or
1 ppb
10% or
100 ppt
40% or
2 ppb
15% or
250 ppt
24
6
Total Column
250
10
-
-
10 %
1%
20 %
2%
24
6
Total Column
(Troposphere)
250
10
-
-
10 %
1%
20 %
2%
24
6
Note
1)
- Range due to air quality user/process study requirements.
92
Target
Table B.4a: Target and Threshold Requirements for Bromine Oxide (BrO) and Chlorine Oxide (ClO): controllers of ozone
(depleters). Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements
satisfy the needs of at least one user group.
Horizontal
Resolution (km)
Region
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Temporal Resolution
(observing cycle; hrs
Trend
Detection
(% per year)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Lower
1)
Troposphere
250
50
3
1
20% or
20 ppt
10% or
2 ppt
40% or
30 ppt
15% or
3 ppt
72
6
-
Upper
Troposphere
-
-
-
-
-
-
-
-
-
-
-
1)
250
100
3
1
50 % or
20 ppt /
1 ppb
10 %
or
2ppt /
0.2 ppb
80% or
30 ppt /
2 ppb
15% or
5 ppt /
0.4ppb
24
6
0.5
Upper
Stratosphere
/Mesosphere
250
100
3
1
20% or 20
ppt /
1ppb
10% or
2 ppt /
0.2 ppb
40% or
30 ppt /
2 ppb
15% or
5 ppt /
0.5 ppb
24
6
0.5
2)
250
100
-
-
20 %
1%
40 %
2%
24
12
0.5
2)
250
50
-
-
20%
5%
40%
5%
24
12
t.b.d.
Lower
Stratosphere
Total Column
Total Column
(Troposphere)
1)
Target
Note - BrO only (Artic Ozone depletion in Planetary Boundary Layer); first value BrO,second value ClO. Total Bry ca 20 ppt , max. ClO (at 5 hPa) ca 500 ppt.
2)
Note - Only BrO
Note t.b.d. - To be determined
93
Table B.4b: Target and threshold requirements for nitric oxide (NO) and nitrogen dioxide (NO2) - precursor and controller.
Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy the
needs of at least one user group.
Region
Horizontal
Resolution (km)
Threshold
Target
Lower
Troposphere
250
Upper
Troposphere
Vertical Resolution
(km)
RMS Error
(by volume)
Bias Error
(by volume)
Temporal Resolution
(observing cycle; hrs
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
10
3
0.5
40%
or 10 ppt
10% or
2 ppt
50% or
15 ppt
15% or
3 ppt
24
6
250
30
3
0.5
40%
or 20 ppt
10% or
3 ppt
50% or
20 ppt
15% or
5 ppt
24
6
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
250
30
4
0.5
30%
or 100 ppt
10% or
40 ppt
40% or
150 ppt
15% or
50 ppt
24
6
250
30
4
0.5
30%
or 150 ppt
10% or
50 ppt
40% or
250 ppt
15% or
75 ppt
24
6
Total Column
2)
NO2 only
250
30
-
-
10 %
1%
20 %
2%
24
6
Total Column
(Troposphere)
250
30
-
-
10 %
1%
20 %
2%
24
6
1)
1)
Note - Lower range due to air quality user/process study requirements
2)
10
12
-2
Note - Total column density range: 2* 10 to 2*10 molecules m (day/night difference taken into account)
94
Target
Table B.5a: Requirements for temperature (requirements from the IGOS Upper Air Group). Target requirements for bias error
and RMS error are consistent with trend requirements. Threshold requirements satisfy the needs of at least one user group.
Region
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
Bias Error
Temporal Resolution
(observing cycle;
hours)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Lower
Troposphere
500
10
3.0
0.1
3.0K
0.5K
n/s
n/s
24
6
Upper
Troposphere
500
10
3.0
0.5
3.0K
0.5K
n/s
n/s
24
6
Lower
Stratosphere
500
10
3.0
0.5
3.0K
0.5K
n/s
n/s
24
6
Upper
Stratosphere
/Mesosphere
500
50
10.0
1.0
5.0K
0.5K
n/s
n/s
24
6
Note n/s – Not specified
95
Target
Table B.5b: Requirements for wind data (requirements from the IGOS Upper Air Group). Target requirements for bias error and
RMS error are consistent with trend requirements. Threshold requirements satisfy the needs of at least one user group.
Region
Horizontal
Resolution (km)
Threshold
Vertical Resolution
(km)
Target
Threshold
10
5
RMS Error
Target
Threshold
Target
0.1
10 m/s
1 m/s
Bias Error
Threshold
Target
n/s
n/s
Temporal Resolution
(observing cycle;
days)
Threshold
Target
12/24
1/48
Lower
Troposphere
500
Upper
Troposphere
500
10
10
0.5
10
1
n/s
n/s
12/24
1/48
Lower
Stratosphere
500
10
10
0.5
10
1
n/s
n/s
12/24
1/48
Upper
Stratosphere
/Mesosphere
500
50
5
2.0
10
3
n/s
n/s
6/24
3/24
Note n/s – Not specified
96
Table B.6a: Requirements for aerosol and PSC presence. Target requirements for bias error and RMS error are consistent
with trend requirements. Threshold requirements satisfy the needs of at least one user group.
Aerosol/PSC Presence
Height interval
Lower
troposphere
Upper
troposphere
Lower
stratosphere
Horizontal
Resolution (km)
Threshol Target
d
1
250
10
Site for Heterogeneous Chemistry and Contributor to Radiative forcing
Vertical Resolution
(km)
Threshold Target
Aerosol parameters of highest
2
significance
Observation frequency
(hours)
Threshold
Target
2
0.5
UV extinction, surface per volume
72
6
Surface per volume, UV extinction
72
6
Aerosols
PSCs
168
6
Surface, single
scattering albedo
Surface, single
scattering albedo
(thermal)
250
20
2
1
250
20
2
0.5
Upper
stratosphere/
Mesosphere
Total column
250
20
3
1
Surface per volume
168
6
250
20
-
-
Spectral optical depth
168
6
Tropospheric
column
250
20
Spectral optical depth
72
6
1)
Note - Lower range due to air quality requirements.
2)
Note - Due to the low level of experience in deriving aerosol parameters on global scale from remote sensing error bars cannot be given yet.
97
Table B.6 b: Target and threshold requirements for aerosol extinction (nadir and limb) and derived parameters ( sunphotometry or
shadow-band radiometry for ground-based measurements) - heterogeneous chemistry and climate impact and atmospheric
correction. Target requirements for bias error and RMS error are consistent with trend requirements. Threshold requirements satisfy
the needs of at least one user group.
Region
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
(Precision)
6)
AOD
Threshold Target
Bias Error
(Accuracy)
6)
AOD
Threshold Target
Temporal Resolution
(observing cycle;
hrs)
Threshold Target
Trend
(% per
year)
Threshold
Target
Threshold
Target
250
20
3
0.1
0.01
0.001
0.05
0.002
168
6
1 % or
5)
>20%
250
20
3
0.1
0.02
0.005
0.05
0.01
72
6
1%
250
20
-
-
0.15
0.004
0.2
0.006
168
6
1 % or
5)
>20 %
250
20
-
-
0.2
0.01
0.3
0.02
72
6
1%
Total Column
250
20
-
-
0.2
0.004
0.3
0.006
168
6
1%
Lower
3)
Troposphere
250
10
3
0.1
0.05
0.01
0.07
0.02
72
6
1%
Lower
1)
Stratosphere
Upper
1)
Troposphere
Total Column
2)
Stratosphere
Total Column
3)
Troposphere
4)
2)
1)
5)
Note - From limb measurements at defined tangent heights.
2)
Note - Integrated over stratospheric limb profile.
3)
Note - Combining nadir and limb
4)
Note - Lower range due to air quality user requirements: visual range.
5)
Note - Larger value to detect major volcanic aerosol build up and decay in stratosphere.
6)
Note - Aerosol Optical Depth: I / I0 = exp ( - AOD * air mass factor); Rayleigh scatter and gas- absorption subtracted; there exists significant dynamic
ranges of AOD in loer stratosphere for background and volcanic eruptions and in lower troposphere, upper troposphere for background and
duststorms, pollution episodes which are reflected in target and threshold values.
98
Table B.6c: Target and threshold requirements for aerosol size distribution, surface area, volume (derived parameters) and
composition - heterogeneous ozone chemistry and climate. Target requirements for bias error and RMS error are consistent
with trend requirements. Threshold requirements satisfy the needs of at least one user group.
Region
Note
Horizontal
Resolution (km)
Vertical Resolution
(km)
RMS Error
1)
(precision -% for all
parameters)
Bias Error
1)
(accuracy - % for all
parameters)
Temporal Resolution
(observing cycle;
hrs)
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Target
Threshold
Target
Lower
Troposphere
250
10
3
0.1
20
5
30
5
72
6
Upper
Troposphere
250
20
3
0.1
30
10
50
10
72
6
Lower
Stratosphere
250
20
3
0.1
30
5
50
10
168
6
Total Column
Stratosphere
250
20
-
-
30
5
40
10
168
6
Total Column
n.r.
n.r.
-
-
n.r.
n.r.
n.r.
n.r.
n.r.
n.r.
2)
1)
- Expressed as percent deviation from reference method: in situ determination of size distribution and composition (in stratosphere: Wyoming dust sonde;
in troposphere: aerosol size distribution instruments; for compostion: filter collection followed by chemical analysis). Volume at 20 km: 0.05 to 10 cubic
micrometers. Lower range due to air quality user requirements.
Note n.r.- Not relevant / not requested.
99
Table B.6d: Target and threshold requirements for aerosol backscatter (mid-visible) and derived parameters (radio sondes
form calibration basis for profiling from ground stations). Target requirements for bias error and RMS error are consistent with
trend requirements. Threshold requirements satisfy the needs of at least one user group.
Region
Horizontal
Resolution (km)
Threshold
Target
Lower
Troposphere
250
Upper
Troposphere
3)
Vertical Resolution
(km)
RMS Error
Bias Error
Target
Threshold
10
2
0.05
t.b.d.
t.b.d.
t.b.d.
t.b.d.
72
6
t.b.d
250
20
2
0.05
t.b.d.
t.b.d.
t.b.d.
t.b.d.
72
6
t.b.d
Lower
Stratosphere
Upper
Stratosphere
/Mesosphere
250
20
2
0.05
0.1*R
168
6
1% or
2)
>20%
250
20
-
-
1*E
2)
1 / sr
-4
5*E
1 / sr
3*E
2)
1 / sr
-4
1.5*E
1 / sr
168
6
1% or
2)
>20 %
Total Column
250
20
-
-
t.b.d.
t.b.d.
t.b.d.
t.b.d.
168
6
t.b.d.
Total Column
(Troposphere)
250
20
-
-
t.b.d.
t.b.d.
t.b.d.
t.b.d.
72
6
t.b.d.
3)
1)
0.01*R
-6
Threshold
3)
0.2*R
3)
Target
0.02*R
Threshold
Trend
Detection
(% per year)
Threshold
1)
Target
Temporal Resolution
(observing cycle;
hrs)
3)
-5
Target
Note - Lower range due to air quality user/process study requirements.
2)
Note - Upper range to detect major volcanic aerosol build up and decay in stratosphere.
3)
Note - R = Rayleigh.
Note t.b.d.- Local density profile and chemical composition must be known at the time and place of backscatter measurement (due to local variability currently
unknown).
100
ANNEX C
THE DATA RECORDS OF REGULARLY REPORTING
GROUND-BASED OZONE STATIONS
101
102
Data Records of Regularly Reporting Ground-Based Ozone Stations
Station Name
Amundsen-Scott (US)
Argentine Islands (UK)
Arrival Heights (NZ)
Belgarno II (Italy)
Halley Bay (UK)
King Edward Pt. (UK)
Marambio (Arg.)
Mirny (Russia)
Syowa (Japan)
Buenos Aires
Comodoro Rivadavia
Ushuaia
Brisbane
Darwin
Macquarie Island
Melbourne/Aspendale
Perth
Uccle
Cachoeira Paulista
Cuiaba
Natal
Sofia
Alert
Churchill
Edmonton
Eureka
Goose Bay
Halifax
Montreal
Regina
Resolute
Saskatoon
Saturna Island
Toronto
Winnipeg
Linan
Country
Antarctica
Antarctica
Antarctica
Antarctica
Antarctica
Antarctica
Antarctica
Antarctica
Antarctica
Argentina
Argentina
Argentina
Australia
Australia
Australia
Australia
Australia
Belgium
Brazil
Brazil
Brazil
Bulgaria
Canada
Canada
Canada
Canada
Canada
Canada
Canada
Canada
Canada
Canada
Canada
Canada
Canada
China
Lat.
-90.00
-65.25
-77.83
-77.87
-73.52
-54.52
-64.23
-66.65
-69.00
-34.58
-45.78
-54.85
-27.42
-12.42
-54.50
-37.80
-31.92
50.80
-22.68
-15.60
-5.84
42.82
82.50
58.75
53.55
79.98
53.55
44.74
45.68
50.21
74.72
52.11
48.78
43.78
49.90
30.30
Lon.
N/A
-64.52
166.67
-34.63
-26.73
-36.50
-56.72
93.00
39.58
-58.48
-1.34
-68.31
153.12
130.88
158.97
144.97
115.95
4.35
-45.00
-48.40
-35.21
23.38
-62.30
-94.07
-114.10
-85.93
-60.30
-63.67
-73.75
-104.71
-94.98
-106.71
-123.13
-79.47
-97.24
119.73
Alt (m)
2810
10
250
255
31
2
196
30
21
25
43
7
3
31
6
125
2
100
573
990
32
588
62
35
766
10
44
31
31
592
64
550
178
198
239
0
Dobson
Start
01.Nov.61
19.Mar.57
01.Jan.88
Brewer
M-83
M-124
01.Jan.73
01.Aug.88
Stop
20.Jan.92
17.Sep.56
02.Apr.82
15.Aug.87
08.Feb.66
01.Oct.65
01.Sep.95
01.Sep.94
01.Feb.57
01.Apr.90
01.Mar.63
01.Jul.55
30.Jun.73
11.Aug.65
08.May.74
01.Oct.90
19.Nov.78
01.Apr.64
01.Dec.58
10.Dec.64
07.Jul.57
01.Jan.62
07.Jul.57
01.May.83
12.Aug.58
103
01.Dec.93
19.Jul.83
01.Oct.90
01.Oct.94
13.Dec.87 28.Oct.87
31.Aug.89 03.Jun.86
31.Mar.88 01.Oct.84
01.Jan.91
30.Sep.88 10.Jul.85
10.Jun.92
01.Feb.93
01.Mar.94
31.Aug.90 01.Apr.87
01.May.83
01.Jan.90
07.Dec.83
01.Jul.92
01.Jan.91
Data Records of Regularly Reporting Ground-Based Ozone Stations
Station Name
Longfengshan
Mt. Waliguan
Xianghe
Hradev Kralove
Copenhagen
Aswan
Cairo
Sodankyla
Biscarrosse/SMS
Haute Provence
Magny-Les-Hameaux
Tbilisi
Cologne
Hohenpeissenberg
Lindenberg
Potsdam
Athens
Thessaloniki
Sondrestrom
Budapest-Lorinc
Reykjavik
Ahmedabad
Kodaikanal
Mt. Abu
New Delhi
Poona
Srinagar
Varanasi
Valentia
Brindisi
Cagilari/Elmas
Ispra (Varese)
Messina
Naples
Rome
Sestola
Country
China
China
China
Czech Rep.
Denmark
Egypt
Egypt
Finland
France
France
France
Georgia
Germany
Germany
Germany
Germany
Greece
Greece
Greenland
Hungary
Iceland
India
India
India
India
India
India
India
Ireland
Italy
Italy
Italy
Italy
Italy
Italy
Italy
Lat.
44.75
36.17
39.98
50.18
55.72
23.97
30.08
67.40
44.73
43.93
48.73
41.68
50.93
47.80
52.21
52.22
37.98
40.51
67.00
47.43
64.13
23.03
10.23
24.60
28.65
18.53
34.10
25.32
51.93
40.65
39.25
45.80
38.20
40.85
40.90
44.22
Lon.
127.60
100.43
116.37
15.83
12.56
32.45
31.28
26.60
-1.23
5.70
2.07
44.95
6.93
11.02
14.12
13.05
23.73
22.97
-50.62
19.18
-21.90
72.65
77.47
72.70
77.22
73.85
74.80
83.03
-10.25
17.95
9.05
8.63
15.55
15.25
12.52
10.77
Alt (m)
UNK
3816
80
285
50
190
37
179
18
684
165
490
50
975
112
89
10
50
300
139
60
55
2343
1220
220
559
1586
76
14
5
240
240
51
45
UNK
1030
Dobson
Start
Brewer
M-83
M-124
01.Jan.74
01.Jun.86
Stop
01.Jan.91
01.Sep.93
01.Jan.79
01.Jan.61
15.Dec.93
01.Jun.92
01.Dec.84
01.Nov.67
01.May.88
16.Mar.76
02.Sep.83
12.Jun.80
01.Jan.76
11.May.67
01.Jan.92
01.Jan.64
01.Oct.89
01.Jan.86
01.Jan.92
01.May.87
12.Mar.82
28.Jun.89
01.Jan.70
19.Jan.61
24.Jan.60
01.Jul.57
27.May.57
01.Jan.55
01.Mar.73
25.Nov.56
01.Dec.63
01.Mar.94
15.Mar.94
01.Jan.92
01.Sep.82
30.Jun.54
01.Jan.87
10.Apr.58
01.Jan.76
104
01.Jan.92
01.Jan.87
01.Jan.86
01.Jan.90
Data Records of Regularly Reporting Ground-Based Ozone Stations
Station Name
Vigna Di Valle
Kagoshima
Minamitorishima
Naha
Sapporo
Tsukuba/Tateno
Alma-Ata
Aralskoe More
Atiray (Gurev)
Karaganda
Semiplatinsk
Nairobi
Pohang
Seoul
Riga
Petaling Jaya
Mexico City
Casablanca
Maputo
DeBilt
Invercargill
Lauder
Lagos
Ny Alesund
Oslo
Tromso
Quetta
Huancayo
Manila
Belsk
Angra Do Heroismo
Funchal (Madeira)
Lisbon
Penhas Douradas
Kunming
Bucharest
Country
Italy
Japan
Japan
Japan
Japan
Japan
Kazakhstan
Kazakhstan
Kazakhstan
Kazakhstan
Kazakhstan
Kenya
Korea
Korea
Latvia
Malaysia
Mexico
Morocco
Mozambique
Netherlands
New Zealand
New Zealand
Nigeria
Norway
Norway
Norway
Pakistan
Peru
Philipines
Poland
Portugal
Portugal
Portugal
Portugal
PR China
Romania
Lat.
42.08
31.55
24.30
26.20
43.05
36.05
43.23
46.78
47.03
49.80
50.35
-1.27
36.03
37.57
57.19
3.10
19.33
33.57
-25.97
52.00
-46.42
-45.03
6.60
78.89
59.91
69.65
30.11
-12.05
14.63
51.84
38.66
40.42
38.77
40.42
25.03
44.48
Lon.
12.22
130.55
143.97
130.55
141.33
140.10
76.93
61.67
41.85
73.13
80.25
-36.80
129.38
126.95
24.25
101.65
-99.18
-7.67
-48.40
5.18
168.32
169.68
3.33
11.88
10.72
18.95
66.57
-75.32
121.83
20.79
-27.22
-7.55
-9.15
-7.55
102.68
26.13
Alt (m)
262
31
9
27
19
21
847
56
0
553
206
1710
6
84
7
46
2268
55
70
1
1
370
10
15
90
100
1721
3313
61
180
74
49
105
1380
1917
100
105
Dobson
Start
10.Jan.56
01.Nov.63
Brewer
M-83
M-124
01.Jan.73
01.Jan.74
01.Jan.74
01.Jan.73
01.Nov.75
01.Aug.85
01.Jul.85
01.Aug.84
01.Aug.84
01.Jul.85
26.Feb.73
16.Aug.84
11.May.79
01.Jan.91
Stop
17.Jul.86
15.Nov.93
01.Apr.74
10.Oct.61
13.Apr.59
19.Apr.84
01.Jan.94
07.May.84
01.Oct.92
01.Jun.74
29.May.89
29.May.89
17.Dec.93
01.Jan.70
01.Jan.87
01.Apr.93
01.Nov.66
17.Jun.69
01.Jan.43
01.Jun.57
14.Feb.62
06.Dec.78
20.Mar.63
30.Jun.67
01.Jan.80
01.Jan.80
30.Sep.87
01.May.90
01.Jan.94
31.Dec.92
12.Feb.91
11.Jul.92
01.Oct.89
01.Jul.89
15.Oct.94
Data Records of Regularly Reporting Ground-Based Ozone Stations
Station Name
Archangelsk
Bolshaya Elan
Dikson Island
Ekaterinburg
Hanty Mansijsk
Heiss Island
Igarka
Irkutsk
Kislovodsk
Kotelnyj Island
Krasnoyarsk
Markovo
Moscow
Murmansk
Nagaevo
Nikolaevsk-Na-Amure
Obninsk
Olenek
Omsk
Pechora
Petropavlovsk/Kamchatski
Samara (Kuibyshev)
St. Petersburg
Tiksi
Tura
Vitim
Vladivostok
Volgograd
Voronez
Yakutsk
Cimljansk
Poprad-Ganovce
Pretoria/Irene
El Arenosillo
Izana (Tenerife)
Madrid
Country
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Russia
Slovakia
South Africa
Spain
Spain
Spain
Lat.
64.58
46.92
73.50
56.80
60.97
80.62
67.47
52.26
43.73
76.00
56.00
64.68
55.75
68.97
59.58
53.15
55.50
68.50
54.93
65.12
53.15
53.25
59.97
71.58
64.17
59.45
43.12
48.58
51.70
62.08
47.73
49.03
-25.73
37.10
28.29
40.45
Lon.
40.50
142.73
80.23
60.63
69.07
58.10
86.57
104.35
42.66
137.90
92.88
170.42
37.67
33.05
150.78
140.70
36.20
112.43
73.40
57.10
140.70
50.45
30.30
128.92
100.07
112.58
131.90
45.72
39.17
129.75
42.25
20.32
28.18
-6.73
-16.49
-3.72
Alt (m)
UNK
22
18
290
40
20
20
467
2070
UNK
137
22
187
46
118
46
UNK
127
119
61
78
137
74
8
UNK
186
80
UNK
147
98
64
706
1'524
41
2367
UNK
Dobson
Start
Brewer
M-83
M-124
01.Aug.73
01.Jan.74
01.Mar.73
01.Jan.73
01.Jan.74
01.Jan.74
01.Mar.73
01.Jan.73
01.Jul.84
01.Jul.83
01.Apr.85
01.Sep.85
01.Sep.84
01.Mar.87
01.Jan.87
01.Jul.85
01.Feb.74
01.Jan.73
01.Feb.73
01.Jan.73
01.Feb.73
01.Feb.73
01.Jan.74
01.Jul.87
01.Jul.85
01.Aug.86
01.Jul.84
01.Jul.85
01.Aug.85
10.Jan.87
01.Jan.74
01.Jan.73
01.Feb.73
01.Jan.73
01.Jan.73
01.Jan.73
01.Apr.75
01.Jan.74
01.Mar.73
01.Jan.73
01.Oct.74
01.Jan.74
01.Feb.73
01.Jan.74
01.Jan.87
01.Aug.84
01.Feb.85
01.Sep.84
01.Sep.84
01.Jan.85
01.Jan.87
01.Aug.87
01.Jan.87
01.Aug.84
01.Jan.87
01.Jul.84
01.Oct.85
01.Jul.85
Stop
01.Jan.90
01.Mar.89
01.Jan.91
10.May.91
01.Jan.88
20.Aug.93
01.Aug.89
01.Jan.76
01.May.91
01.Jan.91
106
01.May.91
01.Jan.91
Data Records of Regularly Reporting Ground-Based Ozone Stations
Station Name
Country
Lat.
Murcia
Norkoping
Vindeln
Arosa
Dushanbe
Chengkung
Taipei
Bangkok
Songkhla
Ashkabad
Cardzou
Bracknell
Camborne
Lerwick
Mahe (Seychelles)
St. Helena
Fedosija
Kiev
Lwow
Odessa
Salto
Barrow
Spain
Sweden
Sweden
Switzerland
Tadzikhstan
Taiwan
Taiwan
Thailand
Thailand
Turkmenistan
Turkmenistan
UK
UK
UK
UK Islands
UK Islands
Ukraine
Ukraine
Ukraine
Ukraine
Uruguay
USA
38.00
58.58
64.24
46.78
38.58
23.10
25.03
12.67
7.20
37.97
39.08
51.38
50.22
60.13
-4.68
-15.93
45.03
50.40
49.82
46.48
-31.38
71.32
Bismarck
USA
46.77
Boulder
USA
40.03
Caribou
Fairbanks/Poker Flat
USA
USA
46.87
64.82
Hanford/Fresno
USA
36.32
Mauna Loa
USA
19.53
Nashville
Samoa
USA
USA
36.25
-14.25
Tallahassee
Wallops Island
USA
USA
30.40
37.93
Lon.
1.17
16.15
19.77
9.68
68.78
121.37
121.53
100.61
100.60
58.33
63.60
-0.78
-5.32
-1.18
55.53
-5.65
35.38
30.45
23.95
30.63
57.97
156.60
100.75
105.25
-68.03
147.87
119.63
155.58
-86.57
170.56
-84.35
-75.48
Alt (m)
Dobson
Start
69
43
225
1840
825
0
25
53
13
227
191
70
88
80
6
460
26
121
325
42
31
11
01.Apr.96
05.Jun.86
511
01.Jan.63
1640
03.Dec.63
192
138
01.Jan.63
06.Mar.84
73
06.Oct.82
3397
01.Dec.63
182
82
01.Jan.63
01.Dec.75
21
13
01.May.64
23.Jun.67
Brewer
M-83
M-124
01.Jan.73
01.Nov.84
Stop
01.May.95
02.Feb.87
01.Jan.92
23.Jul.26
01.Jul.65
01.Jan.78
01.Dec.88
01.Jan.90
01.Jul.87
01.Jan.97
01.Jan.97
01.Jan.74 01.Jul.87
01.Sep.74 01.Aug.84
01.Jan.67
01.Jan.91
01.Mar.52
10.Nov.75
18.Jan.77
01.Jan.73
01.Jan.73
01.Aug.74
01.Jan.73
107
01.Jan.86
15.Nov.97
01.Jul.84
01.Jun.85
01.Aug.85
01.Aug.84
108
ANNEX D
EXAMPLES OF AIRBORNE RESEARCH CAMPAIGNS
109
110
Examples of Airborne Research Campaigns - Stratospheric
Name
Date
Region
Platform
Description
Stratospheric-Tropospheric Austral
Exchange Project (STEP) Summer/Fall
1987
Southern Hemisphere subtropical latitudes from Darwin,
Australia
ER-2
Investigate mechanism and rates of irreversible transfer of mass,
trace gases, and aerosols from the troposphere to the stratosphere
and within the lower stratosphere and to explain the observed
extreme dryness of the stratosphere
Airborne Antarctic Ozone
Experiment (AAOE)
Austral
Winter/Spring
1987
Southern Hemisphere polar
regions from Punta Arenas,
Chile
ER-2 and DC-8
To establish the processes responsible for the Antarctic ozone hole
Airborne Arctic
Stratospheric Expedition
(AASE)
Winter 1989
Northern Hemisphere polar
regions from Stavanger,
Norway
ER-2 and DC-8
To study the production and loss mechanisms of ozone in the north
polar stratosphere and to study the effects of PSCs on the ozone
distribution within the Arctic polar vortex
European Arctic
Stratospheric Ozone
Experiment (EASOE)
Winter 1991-92
Northern Hemisphere high
latitudes in Scandinavia
TRANSALL,
ARAT, Falcon,
balloons and
ground-based
instruments
To study the chemical loss of ozone in the north polar stratosphere
Second Airborne Arctic
Stratospheric Expedition
(AASE-II)
Winter 1991-92
Northern Hemisphere high
latitudes from Fairbanks, AK
and Bangor, ME
ER-2
To examine whether significant ozone erosion will occur within the
Arctic vortex as chlorine loading in the stratosphere approaches the
expected 5 ppbv and to investigate the mechanisms responsible for
the observed ozone erosion pole-ward of 30 degrees in the
winter/spring northern hemisphere reported from satellite
observations
Stratospheric Photochemistry, Aerosols, and
Dynamics Expedition
(SPADE)
late 1992 and
early 1993
Northern Hemisphere midlatitudes from Moffett Field,
CA
ER-2
To study chemical processes potentially affecting ozone at altitudes
most strongly influenced by stratospheric aviation, to examine
distributions of tracers whose concentrations in the lower
stratosphere vary on time scales ranging from months to years, and
to determine the effects of heterogeneous chemistry on
concentrations of radicals and reservoir species
111
Examples of Airborne Research Campaigns - Stratospheric
Name
Date
Region
Platform
Airborne Southern
Hemisphere Ozone
Experiment;
Measurements for
Assessing the Effects of
Stratospheric Aircraft
(ASHOE/MAES)
late March early April, late
May - early
June, late July early August,
October 1994
Northern Hemisphere midlatitudes from Moffett Field,
CA, tropical and subtropical
latitudes from Barbers Point,
HI and Nada, Fiji, and
Southern Hemisphere midand high latitudes from
Christchurch, NZ
ER-2 and ground- To examine the causes of ozone loss in the Southern Hemisphere
lower stratosphere, to investigate how the loss is related to polar,
based
mid-latitude, and tropical processes, and to provide information about
instruments
stratospheric photo-chemistry and transport for assessing the
potential environmental effects of stratospheric aircraft
Second European
Stratospheric Arctic and
Mid-latitude Experiment
(SESAME)
Summer 1994 Summer 1995
Northern Hemisphere mid and TRANSALL,
high latitudes over Europe and ARAT, Falcon,
balloons and
Scandinavia
ground-based
instruments
Stratospheric Tracers of
Atmospheric Transport
(STRAT) and Observations
from the Middle
Stratosphere
May 1995, Oct. Nov., 1995, Jan.
- Feb., 1996,
Jul. - Aug.,
1996, Sept.
1996, Dec. 1996
Aircraft flights at Northern
Hemisphere mid-latitudes from
Moffett Field, Ca and at
tropical and subtropical
latitudes from Barbers Point,
HI. Balloon flights from Ft.
Sumner, NM and Juazerio du
Norte, Brazil
ER-2, balloons,
and groundbased
instruments
Description
To study the chemical loss of ozone in the north polar stratosphere
and the impacts on mid-latitudes
To measure the morphology of long-lived tracers and dynamical
quantities as functions of altitude, latitude, and season in order to
help determine rates for the global-scale transport and future
distributions of gases and aerosols in the stratosphere
DC-8
Northern Hemisphere midand high latitudes from Moffett
Field, CA and Fairbanks, AK;
tropical and subtropical
latitudes from Barbers Point,
Hawaii
Spring 1996 and Western Europe
Fokker27
Transport of Ozone And
Stratospheric-Tropospheric Winter 1997
Exchange (TOASTE)
To examine small scale features in ozone and methane (filaments)
which are believed responsible for the exchange of trace gases
between the tropical region and mid-latitudes, and the polar region
and mid-latitudes.
Airborne Polar Experiment
(APE-1)
Investigation of PSCs at high northern latitudes
Tropical Ozone Transport Dec., 1995 Experiment / Vortex Ozone Feb., 1996
Transport Experiment
(TOTE/VOTE)
Dec. 1996 - Jan. Northern Scandinavia
1997
Geophysika,
Falcon
112
To establish the processes responsible for stratosphere-troposphere
exchanges and quantify the ozone fluxes during specific episodes
Examples of Airborne Research Campaigns - Stratospheric
Name
Date
Photo-chemistry of Ozone Spring, Summer
Loss in the Arctic Region in and Fall, 1997
Summer (POLARIS) and
Observations from the
Middle Stratosphere (OMS)
Region
Platform
Description
Airborne flights at Northern
Hemisphere mid- and high
latitudes from Fairbanks, K;
tropical and subtropical
latitudes from Barbers Point,
HI as a STRAT follow-on,
Balloon flights from Ft.
Sumner, NM, Fairbanks, AK,
and Juazerio du Norte, Brazil
ER-2, balloons,
and groundbased
instruments
To understand the natural cycle of polar stratospheric ozone as it
changes from very high concentrations in spring down to very low
concentrations in Autumn and to examine the seasonal behavior of
latitudinal atmospheric transport
Falcon
Investigation of the effects of aviation emissions on the atmosphere
Pollution from Aircraft
Emissions in the North
Atlantic flight corridor
(POLINAT-2)
Sept.-Oct., 1997 Eastern Atlantic and Western
Europe
Third European
Stratospheric Experiment
on Ozone (THESEO,
THESEO-2000)
Main campaigns
in Winter 19981999, Winter
1999-2000
Aircraft flights from
Scandinavia and Western
Europe, Indian Ocean,
northern Africa; balloon flights
from Kiruna, Sweden and from
Aire-Sur-L'Adour and Gap,
France
ARAT, Mystere20, Falcon,
Geophysica,
balloons and
ground-based
instruments
To improve understanding of the causes of ozone depletion over
Europe and other mid-latitude regions, and understand the transport
mechanisms between mid-latitudes and sub-tropical latitudes
Airborne Polar Experiment
- Tropics (APE-THESEO)
Feb.-March,
1999
Seychelles, Indian Ocean
Geophysika,
Falcon
To study what controls the low water content of the stratosphere, the
mechanisms of cloud formation in the tropical tropopause region and
its impact on ozone depletion and troposphere-stratosphere
exchange of gases and particles, and what role do the tropics play in
the origin of the global stratospheric aerosol layer
Airborne Polar Experiment
– Geophysica Aircraft in
Antarctica (APE-GAIA)
Sept.-Oct., 1999 Antarctica
Geophysica
To investigate Antarctic ozone chemistry during the transition period
between the depletion phase (August-September) and the recovery
phase (October-November), and clarify the extent and altitude region
of mixing of polar air masses with middle latitudes
SAGE III Ozone Loss and
Validation Experiment
(SOLVE)
Winter 19992000
ER-2, DC-8,
balloons, and
ground-based
instruments
To examine the processes which control polar to mid-latitude
stratospheric ozone levels in order to gain a better understanding of
the possibility of continuing ozone loss and of expected recovery
over the next several decades, and to acquire correlative
measurements needed to validate the SAGE III satellite instrument
Aircraft and balloon flights at
Northern Hemisphere midand high latitudes from Kiruna,
Sweden
113
Name
Date
Examples of Airborne Research Campaigns - Tropospheric
Region
Platform
Description
Chemical
Instrumentation and
Test Experiment
(CITE-1)
Nov., 1983 and
April, 1984
Western US and Central
North Pacific, Hawaii
CV-990
Airborne inter-comparison of NO, CO, and OH measurement
techniques; increased confidence in CO and NO measurements;
eliminated insufficiently sensitive OH techniques; and provided
baseline measurements of NO and CO over the north central Pacific
Atmospheric Boundary
Layer Experiment
(ABLE-1)
June, 1984
Tropical North Atlantic
from Barbados
Electra
Airborne study of boundary layer chemistry and dynamics over the
tropical Atlantic Ocean and the French Guinea rainforest. Provided
striking new insights into marine boundary layer sulphur transport and
demonstrated the great importance of transported Saharan dust as a
nutrient source to the tropical Atlantic Ocean comparable to the outflow
from the Amazon River.
Atmospheric Boundary
Layer Experiment
(ABLE-2A)
August, 1985
Central regions of Brazil's Electra and
Amazon rainforest,
ground-based
Manaus, Brazil
First and still the largest joint US/Brazilian study of basin-scale
biosphere-atmospheric interactions and tropospheric chemistry over
the Brazilian Amazon rainforest during the dry season in the southern
hemisphere. Used co-ordinated airborne and ground based
measurements. Provided important new estimates of CH4 emissions
from the tropics, revised tropical convective cloud models, and allowed
new estimates of O3 photochemical production. Produced the
surprising result that transport of dust from Africa may have served to
fertilise the Amazon rainforest.
Chemical
Instrumentation and
Test Experiment
(CITE-2)
August, 1986
Wallops Flight Facility
and California
Airborne inter-comparisons of NO, NO2, PAN, and HNO3 instruments·
Demonstrated capability for baseline measurements for NO & PAN
and for NO2 under some atmospheric conditions and indicated need
for additional R&D for HNO3 measurements.
Atmospheric Boundary
Layer Experiment
(ABLE-2B)
May, 1987
Central regions of Brazil's Electra and
Amazon rainforest,
ground-based
Manaus, Brazil
Joint US/Brazilian study of basin-scale biosphere-atmospheric
interactions and tropospheric chemistry over the Brazilian Amazon
rainforest during the wet season in the Southern Hemisphere
Atmospheric Boundary
Layer Experiment
(ABLE-3A)
August, 1988
Northern latitudes of
Electra and
Alaska from Point Barrow ground-based
and Bethel, AK
Co-ordinated air and ground based study of O3 photo-chemistry and
biogenic sources of tropospheric green house gases in Alaska. First
regional scale measurement of the flux of CH4 from the Alaskan
Wetlands using co-ordinated ground-base and airborne flux
techniques, and satellite observations for regional scaling of flux
measurements. Provided important new input to photochemical
models that showed sensitivity of the high latitudes to long range
transport of natural and anthropogenic emissions.
Electra
114
Name
Date
Chemical
Instrumentation and
Test Experiment
(CITE-3)
Sept., 1989
Atmospheric Boundary
Layer Experiment
(ABLE-3B)
July, 1990
Pacific Exploratory
Sept.-Oct., 1991
Mission (PEM) WEST A
Transport and Chemistry October, 1992
Near the Equator
(TRACE-A)
Pacific Exploratory
March, 1994
Mission (PEM) WEST B
Examples of Airborne Research Campaigns - Tropospheric
Region
Platform
Description
North Atlantic midlatitudes from Wallops
Island, VA and tropical
South Atlantic midlatitudes from Natal,
Brazil
Hudson Bay lowlands
from North Bay, Canada
and Northern Quebec and
Labrador from Goose
Bay, Canada
North-western pacific
Ocean
Electra
Airborne inter-comparison of SO2, COS, H2S, CS2, and DMS
measurement techniques in the remote troposphere· Provided high
confidence for measurements of COS, H2S, CS2, and DMS, and
demonstrated the need for additional instrument evaluation for SO2
measurements
Electra and
ground-based
Joint US/Canadian study of high latitude photo-chemistry and biogenic
sources of greenhouse gases. Revised the global emissions of
methane estimates from high latitude wetlands and re-emphasised the
relative importance of tropical wetlands as a natural source of methane
North-western pacific
Ocean
DC-8 and
P-3B
DC-8 and ground- Joint US/Asian study of the impact of Asian continental outflow on the
based
chemistry of the troposphere over the north-western Pacific Ocean
during a period characterised by minimum Asian outflow; Observed
impact of Asian continent several thousand kms into the Pacific, even
during the fall "quiescent" continental outflow period. Found large
scale lofting via convective processes to be a significant source of
sulphur and hydrocarbons in the upper troposphere. Established the
high troposphere at mid-latitudes as a major source of O3, and the
lower and mid troposphere in tropics as a sink. Found lightning in
convective clouds to be a major source of NOx in the high tropical
Pacific troposphere. Demonstrated clear need for further R&D for NOy
and NO2 measurements. Established baseline measurements for the
Pacific troposphere
Tropical Atlantic based
DC-8 and ground- Joint NASA/Brazilian co-ordinated with an European/African study in
from Barasilia, Brazil,
based
Southern Africa to investigate the role of biomass burning plumes in
Johannesburg, South
producing elevated ozone levels over the tropical Atlantic Ocean; ·
Africa, Winhock, Namibia,
Demonstrated conclusively that enhanced O3 detected by satellites
over the tropical Atlantic is photo-chemically produced from emission
and Ascension Island
products of biomass burning products from Africa and Brazil. Found
that the meteorology over the south Atlantic acts to confine these in the
tropical Atlantic basin, thereby providing near ideal conditions for the
formation and accumulation of O3 and other photochemical products
115
Joint US/Asian airborne & ground based study of the impact of Asian
continental outflow on the chemistry of the troposphere over the north
western Pacific Ocean during a period of enhanced outflow
Name
Date
Examples of Airborne Research Campaigns - Tropospheric
Region
Platform
Description
Measurement of Ozone
by Airbus In-service
Aircraft (MOZAIC)
EXPRESSO
Since late 1995
Quasi global
5 commercial
Airbus
climatologies of ozone and water vapour in lower and mid-troposphere
and at flight levels (8-12 km)
Autumn 1996
Central Africa
Fokker27
Pacific Exploratory
Mission in the Tropics
(PEM TROPICS-A)
September, 1996
Remote tropical Pacific
from Christmas Island,
Tahiti, Easter Island,
Christchurch, NZ, Fiji,
and Guayaquil, Ecuador
DC-8 and
P-3B
To quantify the export of chemical species (NOx, CO/CO2, VOCs) from
the forest and savana regions into the Harmattan layer
Coordinated trace gas measurements to study the chemistry of the
remote tropical Pacific troposphere during southern Hemisphere dry
season. First GTE flights to include OH in a science measurement to
provide data to assist in global model development and verification and
to provide baseline measurements of important trace gases in a highly
photochemically active region of the troposphere that is thought to be
the least impacted by human activities. Documented extensive impacts
form long range transport of biomass burning emissions, sulphur
photochemistry and new aerosol formation
North Atlantic Regional
Experiment (NARE 97)
AugustNovember, 1997
North Atlantic
C-130
Chemical processes in the export of polluted air from North America
over the Atlantic.
DC-8 and P-3B
Co-ordinated trace gas measurements aboard to study the chemistry
of the remote tropical Pacific troposphere during the Southern
Hemisphere wet season. new measurements of HOx and sulphur
photo-chemistry and extensive study of new particle formation process
DC-8, P-3B, and
ground-based
measurements
Joint US/Asian quantify the Asian continental outflow and to study the
chemical aging of emissions from the Asian continent and from Europe
over the north-western Pacific Ocean.
Pacific Exploratory
Mission in the Tropics
(PEM TROPICS-B)
March/April, 1999 Remote tropical Pacific
from Christmas Island,
Tahiti, Easter Island,
Christchurch, NZ, Fiji,
and Guayaquil, Ecuador
Transport and Chemistry March/April, 2001 North-western Pacific
Over the Pacific
Ocean and Hong Kong
(TRACE)-P
and Yokota Air Base,
Fussa, Japan
116
ANNEX E
OTHER SPACE-BASED INSTRUMENTS
117
118
Other Space-Based Instruments
The description of space-based instruments used to make measurements relevant to the
Ozone Project in Section 3.3 was limited to those instruments that are currently or are planned to
be part of long term measurement systems involving multiple related instruments and those on
several large research-oriented platforms whose lifetime may be sufficiently long that there is a
reasonable possibility that their data sets will be useful for intermediate to long term studies of the
atmosphere. In selecting this limited set a number of other useful instruments have been left out.
These instruments, which fall into the basic categories of those that have flown previously, those
that are currently flying, and those that are being considered for future use, are summarised here.
E.1
Previously-flown Instruments
E.1.1 Nimbus 7
The Nimbus 7 spacecraft contained several instruments for measuring atmospheric trace
constituents and aerosols. Two of them - the TOMS and SBUV instruments - were described in
Section 3.3.1. Other relevant instruments include the Limb Infrared Monitor of the Stratosphere
(LIMS), the Stratosphere and Mesosphere Sounder (SAMS), and the Stratospheric Aerosol Monitor
(SAM II).
LIMS was an infrared emission instrument that made near-global measurements (64 S 84 N) for the period from October 1978- May 1979. Constituents measured were O3, NO2, H2O,
HNO3, as well as temperature. Two observations per day were made, typically around 1 p.m. and
11 p.m., so that diurnal variations could be studied. Most of the measurements were limited to the
stratosphere, although ozone and temperature measurements extended through much of the
mesosphere.
SAMS made measurements over an approximately three year period of the distribution of
N2O and CH4, concentrating on the middle and upper stratosphere and lower mesosphere. The
SAMS measurements were instrumental in showing the two-dimensional structure of long-lived
tracers in the stratosphere. SAM II was a single channel (1 micron) solar occultation instrument
that operated for nearly 15 years. The SAM II data played a crucial rule in providing knowledge
about the temporal and geographic distribution of PSCs
E.1.2 ATMOS
The first chemically comprehensive set of space-based measurements of a broad range of
atmospheric trace constituents was made by the Atmospheric Trace Molecule Spectroscopy
(ATMOS) instrument, an infrared occultation interferometer, aboard the Spacelab 3 Space Shuttle
mission in April-May, 1985. Data from this mission were limited to two latitude bands - roughly
o
o
30 N and 47 S. ATMOS measured nearly all the important nitrogen-containing species in the
stratosphere (i.e. NO, NO2, N2O5, HNO3, HNO4, ClONO2, N2O), most of the important halogencontaining species (i.e. HCl, ClONO2, HF, CF2O, CF3Cl, CF2Cl2, CH3Cl, CHClF2, CCl4, CF4) and a
variety of other species (i.e. H2O, CH4, CO, OCS, HCN, C2H2, C2H6), including isotopically
substituted forms of O3 and H2O.
Subsequent flights of the ATMOS instrument (March 1992, April 1993 and November
1994), as part of the Atmospheric Laboratory for Applications and Science (ATLAS) series of
shuttle missions, have extended ATMOS coverage to the tropics and high latitudes and have been
used for trend determination through comparison of the mid-1985 and late-1994 observations. In
particular, high northern latitudes were observed by ATLAS-2 in April, 1993, while high southern
latitudes were observed by ATLAS-3 in November, 1994. In both cases, observations were made
while the springtime polar vortices still existed, and comparative observations of air inside and
outside the vortex were carried out.
119
E.1.3 MAS
The Millimetre-Wave Atmospheric Sounder (MAS) instrument flew aboard the Space
Shuttle in 1992, 1993, and 1994 as part of the ATLAS payload. MAS used millimetre-wave
emission techniques to make observations of ozone, water vapour, chlorine monoxide and
temperature. MAS had a high spectral resolution that made it particularly well suited to studying
the mesosphere region, where emission lines are quite narrow and details, such as Zeeman
splitting of molecular oxygen lines, can be observed.
E.1.4 CRISTA/MAHRSI
The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) and
Middle Atmosphere High Resolution Spectrographic Investigation (MAHRSI) flew aboard the
German ASTRO-SPAS satellite which was deployed from and retrieved by the Space Shuttle
during flights in November, 1994, and August, 1997.
CRISTA measures temperature and trace gas concentrations using both infrared and farinfrared wavelengths. There are multiple detectors and three telescopes for the infrared, looking at
slightly different angles from the Shuttle, so that small horizontal scale features can be observed in
the temperature and constituent profiles. These measurements are unique because of this high
resolution and the results show very clear evidence of interesting structural features in the
distributions of relatively long-lived constituents such as ozone and nitric acid. CRISTA
observations extend well into the thermosphere for some species.
MAHRSI is an ultraviolet instrument designed to measure NO and OH, mainly in the
mesosphere and thermosphere. The OH retrieval has recently been extended to 45 km. The initial
results from MAHRSI suggested that mesospheric OH levels were significantly below those
expected based on observed levels of water vapour and ozone and known hydrogen-oxygen
photochemistry.
E.1.5 ADEOS
The Japanese ADEOS spacecraft, which operated for approximately one year (1996-1997)
had several instruments used for making atmospheric chemistry measurements.
The Interferometric Monitor of Greenhouse Gases (IMG), a nadir-observing Michelsen-type
Fourier Transform Spectrometer, was designed to measure several gases, including density
profiles of CO2 and H2O, total ozone column, and mixing ratios of CH4, N2O, and CO in the
troposphere. Its combination of high spectral resolution and a nadir-viewing geometry made it
unique for instruments applied to atmospheric chemistry.
The Improved Limb Atmospheric Spectrometer (ILAS) instrument used the technique of
absorption at solar occultation to measure the vertical profile of ozone, aerosols, and several trace
gases. Both infrared and visible wavelengths were used to determine constituent/aerosol and
pressure/temperature measurements, respectively. The combination of the solar occultation
technique and the polar sun-synchronous orbit of the ADEOS spacecraft, meant that the ILAS
observations were all at high latitudes.
The Retroreflector in Space (RIS) was used in conjunction with laser ground stations to
support vertical profile and/or column measurements of a small number of gases.
E.1.6 SOLSE/LORE
The Shuttle Ozone Limb Sounder Experiment (SOLSE) and Limb Ozone Retrieval
Experiment (LORE) flew aboard the Space Shuttle (STS-97) in the fall of 1997. These instruments
were designed to test the possible use of ultraviolet limb sounding to measure ozone in the
stratosphere and upper troposphere. LORE used optical filters in the ultraviolet, visible, and
120
infrared wavelengths to measure ozone profiles throughout the stratosphere. SOLSE operated at
ultraviolet wavelengths with a two-dimensional detector array to ultraviolet limb scattering
technique., The UV limb scattering technique demonstrated by SOLSE has been selected as the
vertical profiling technique for the OMPS instrument (see Section 3.3.2).
E.2
Currently Flying Instruments
E.2.1 POAM-3
The Polar Ozone Aerosol Monitor (POAM-3) instrument is a solar occultation instrument
similar in spirit to the SAGE instruments. It was built for the US Naval Research Laboratory and
was launched aboard the French SPOT-4 in the winter of 1998. The POAM instrument, an
improved version of the POAM-2 instrument which flew aboard the French SPOT-3 satellite from
1993-1996, uses the solar occultation technique to measure ozone, water vapour, aerosols, polar
stratospheric clouds, temperature, and nitrogen dioxide in the stratosphere.
By flying in a polar, sun-synchronous orbit it obtains information at high latitudes, making it
particularly important for studies of PSCs at high latitudes. The observations should help extend
the PSC climatology derived from SAM II and POAM-2. Its orbital coverage nicely complements
that of the SAGE III instrument planned for the Russian Meteor-3M satellite, as POAM III will
measure mostly very high southern latitudes and mid-high northern latitudes, while SAGE III will
measure moderately high southern latitudes and very high northern latitudes.
E.2.2 UVISI
The Ultraviolet Visible Imagers and Spectrographic Imager (UVISI) instrument flies onboard the Midcourse Space Experiment (MSX) of the US Department of Defense. It is a very high
spectral resolution imager, and can be used in various modes, which include the detection of ozone
by exploiting stellar occultations (see COALA). Its high spectral resolution makes it an excellent
platform for testing remote sensing techniques. However, due to operational constraints associated
with the primary mission of MSX, the UVISI instrument obtained only limited data during the early
phase of MSX operation.
E.2.3 GPS
The Global Positioning System (GPS) provides information on the temperature distribution
of the stratosphere and upper troposphere with high vertical resolution, including excellent
characterisation of the tropopause region. This uses a radio occultation technique based on
sources aboard one set of space-based platforms and receivers on another set of platforms. The
accuracy of the temperature retrievals is reduced as one gets lower down into the troposphere
where water vapour concentrations become sufficiently high that a constant molecular weight for
air can no longer be assumed. GPS observations are well-scattered geographically because the
diversity of GPS sources and observing platforms ensures that the occultations will be well
distributed.
E.2.4 OLME
The Chilean Ozone Layer Monitoring Experiment (OLME) was launched aboard the Chilean
FASat Bravo instrument in the summer of 1998. OLME uses ultraviolet cameras with both charge
coupled device (CCD) and ultraviolet photodiode detectors to measure the total ozone column. It
was designed to concentrate on making observations of ozone in the Antarctic and sub-Antarctic
regions of Chile.
E.2.5 MOPITT
The Measurement of Pollution in the Troposphere (MOPITT) instrument, a Canadian
infrared instrument, measures tropospheric carbon monoxide and is flying aboard EOS Terra.
121
MOPITT observes CO profiles (3-4 levels with resolution of several km are expected to be
retrieved), as well as total column amounts of CO. It also measures total column methane. By
flying aboard Terra, MOPITT also has available coincident measurements of surface properties
that may be particularly useful in studies of the relationships between the land surface (especially
the presence of fires) and atmospheric CO concentrations.
E.3
Future Instruments
E.3.1 COALA
The Calibration for Ozone by Atmospheric Limb Acquisitions instrument (COALA) is a
derivative of the GOMOS (Global Ozone Monitoring by Occultation of Stars) which will fly on ESA’s
ENVISAT satellite which is due for launch in 2001 (see Section 3.3.3). Like GOMOS it exploits the
absorption of ultraviolet and visible radiation during stellar occultation to determine the
concentrations of ozone, water vapour, aerosols and nitrogen dioxide in the stratosphere.
Like all occultation devices this technique is “self-calibrating” and should provide excellent
accuracy and vertical resolution (~1 km). Compared to SAGE its accuracy will be slightly reduced
but, in compensation, it will provide much enhanced geographical coverage. Unlike the UVISI, it
concentrates on exploiting stellar occultation. No firm flight opportunities have emerged yet,
though it has aroused considerable interest as it has been designed for operational use.
E.3.2 ODIN
The ODIN mission, a collaborative effort of scientists from Sweden, France, Canada, and
Finland, will have two instruments designed to study ozone and atmospheric chemistry. These
consist of a radiometer (SMR) using sub-millimetre wavelengths to measure ozone, chlorine
monoxide, water vapour and other constituents, and an Optical Spectrograph and Infrared Imaging
System (OSIRIS) using ultraviolet-visible and near infrared wavelengths for studying ozone, NO2,
aerosols and several other constituents. The launch of ODIN, to a sun-synchronous 600 km orbit,
is scheduled for late 2000 for a two year mission. These are limb scan measurements which will
provide altitude profiles of ozone and over 20 other gases in the stratosphere. ODIN will fly in a
polar orbit along the terminator and will test a tomographic technique for ozone above 50 km.
E.3.3 ILAS-2
The second version of the Improved Limb Atmospheric Spectrometer (ILAS-2), an
occultation-based instrument using both infrared and visible radiation, is scheduled for flight aboard
the Japanese ADEOS-2 spacecraft in 2001.
E.3.4 FTS
Although no plans currently exist for a follow on to EOS-CHEM, a recent long term planning
exercise carried out by NASA calls for the long term measurement of a number of atmospheric
parameters using a series of Fourier-transform infrared spectrometers (FTS) aboard an inclinedorbiting platform (assumed to be the International Space Station, which would allow for combined
flight with the SAGE III instrument).
Coupling this with the provision of a microwave emission instrument in polar sunsynchronous orbit would provide long term continuity of key measurements made by MLS (e.g.
upper troposphere/lower stratosphere ozone, water vapour, and temperature). One or more FTS
instruments similar to that planned for the inclined orbiting platform might also be used on the polar
sun-synchronous platform depending on the completeness of the species set to be measured with
the planned microwave instrument.
122
The first FTS in an inclined orbit would not fly until several years after the launch of EOS
CHEM, and the polar sun-synchronous spacecraft would probably not be launched until
approximately 2007.
E.3.5 ACE
The Atmospheric Chemistry Experiment (ACE) is a Canadian instrument to fly on the
SCISAT-1 satellite of the Canadian Space Agency. The main goal of the ACE mission is to
measure and to understand the chemical and dynamical processes that control the distribution of
ozone in the upper troposphere and stratosphere. A comprehensive set of simultaneous
measurements of trace gases, thin clouds, aerosols, and temperature will be made by solar
occultation from a satellite in low earth orbit. A high inclination (74 degrees) orbit at 650 km will
give ACE coverage of tropical, mid-latitude, and polar regions. The vertical resolution will be better
than 4 km from the cloud tops (or about 5 km for clear scenes) up to about 100 km. A high
-1
resolution (0.02 cm ) infrared Fourier Transform Spectrometer (FTS) operating from 2 to 13
microns will measure atmospheric absorption spectra during sunrise and sunset. Aerosols and
clouds (e.g., PSCs) will also be monitored using the extinction of solar radiation in the visible (0.5
µm) and near infrared (1 µm) regions with two solar imagers. An ultraviolet/visible spectrograph will
probably be included in the mission. ACE is scheduled for launch in 2002 for a 2 year mission.
E.3.6 SWIFT
The Stratospheric Wind Interferometer for Transport Studies (SWIFT) project is intended
for global measurement and analysis of stratospheric winds using a Doppler Michelson
interferometer to detect wavelength shifts in the thermal emission from an ozone line near 9
microns. The measurement concept is based on the WINDII instrument that flies aboard UARS
(see section 3.3.3.a). While WINDII employed non-thermal air glow emission for its Doppler
measurements for the altitude range of 80 to 300 km, the SWIFT instrument will use thermal
emission, making the method effective over the altitude range from 20 to 45 km. Winds are to be
measured with an accuracy of at least 5 m/sec, and ozone concentrations are to be measured
simultaneously to 5 percent. SWIFT is intended to demonstrate the capability of operational
stratospheric wind measurements assimilated into a forecast model, but also will satisfy several
wind-related research objectives. A launch opportunity for SWIFT is being actively sought by the
Canadian Space Agency.
E.3.7 AIRS
The Atmospheric Infrared Sounder (AIRS), a facility instrument selected to fly on NASA's
EOS-Aqua observatory scheduled for launch in December, 2000, is intended to measure primarily
atmospheric state parameters of temperature, humidity, and cloud characteristics. It obtains a
-1
spectrum of the thermal infrared radiation between 650 - 2700 cm with a spectral resolution of
1/1200. At the signal-to-noise of the AIRS detectors (noise equivalent temperatures of 0.2 K at
250 K) it will be possible to infer temperature profiles through the troposphere to six levels in the
stratosphere (100 to 1 mb) with a precision of 2 K in the upper levels. The spectral features of
several atmospheric trace gases, including ozone, will provide at least total column information. It
is planned to include ozone total column amounts as a standard (at launch) product for each AIRS
retrieval footprint (45 km at nadir). The development of other products for routine production (so
called research products) which include ozone profiles at some number of levels (to be
determined), columns or profiles of methane, and CO, will be left until after launch. Pre-launch
simulations suggest that the AIRS retrieved ozone column amounts can be made with a precision
of 2-3%. It is possible that some ozone profile information may be obtained from the AIRS spectra,
but this would be a research product that would probably not be available until some time after the
launch.
123
E.3.8 SABER
The SABER (Sounding of the Atmosphere using Broadband Emission Radiometry)
instrument will fly aboard NASA’s Thermosphere-Ionosphere-Mesosphere Energetics and
Dynamics (TIMED) mission, currently scheduled for launch in the spring of 2001 and an operational
duration of two years. Although the primary scientific goal of TIMED and SABER is to quantify the
basic thermal structure and energy budget of the mesosphere and lower thermosphere (60 to 180
km), SABER will provide information on temperature, density, pressure, trace constituent
distributions, and heating and cooling rates through much of the stratosphere (down to 15 km).
SABER is a 10-channel broadband radiometer with an instantaneous field of view of 2 km that
1
measures infrared limb emission of CO2, O3, NO, O2( ), OH, and H2O. These measurements will
be inverted to yield (as routine, operational products) temperature (15 to 100 km, day and night),
ozone (15 to 95 km, day and night), water vapour (15 to 80 km, day and night), CO2 (80 to 140 km,
daytime only). Additional analyses of the SABER radiance measurements will yield rates of cooling
due to emission by CO2, NO, O3, and H2O and rates of heating due to absorption of solar radiation
(by O3, O2 and CO2, ultraviolet to infrared wavelengths), throughout the middle atmosphere. Rates
of heating due to exothermic chemical reactions will be derived in the mesosphere from the OH
and O2 airglow measurements, day and night. Concentrations of atomic species H (80 to 100 km)
and O (50 to 120 km) will also be inferred using a variety of techniques.
E.3.9 TRIANA
The NASA Triana mission is scheduled for launch in 2001 and will occupy the L-1 Lagrange
libration point (some one million miles from the Earth) to provide continuous coverage of the sunlit
portion of the Earth as it rotates. Observations using the EPIC spectro radiometer will be made
every 15 minutes. This instrument measures radiances at ten wavelengths in the ultraviolet,
visible, and near infrared regions (at 317.5, 325, 340, 388, 393.5, 443, 551, 645, 870, and 905 nm)
that can be transformed into data products (ozone, aerosols, cloud optical depth, cloud height,
sulphur dioxide, precipitable water vapour, volcanic ash, and UV irradiance) every hour for the
entire globe at 8-km surface resolution. The coverage of TRIANA complements that of instruments
aboard polar-orbiting satellites, that make at most two observations of any particular location on
Earth per day (one if using sunlight, such as the UV observations used for many ozone
measurements through the BUV or DOAS technique).
124
ANNEX F
ACRONYM/ABBREVIATION LIST
125
126
Acronym/Abbreviation List
ACE
ACRIM
AGAGE
ARM
ATMOS
BSRN
BUV
CEOS
CFCs
CLAES
CNES
COALA
CRISTA
DOAS
ENVISAT
EOS
ERBS
ERS
ESA
EUMETSAT
FTIR
GAW
GCOS
GEO
GOME
GOMOS
GPS-MET
HALOE
HCFCs
HIRDLS
HIRS
HRDI
IASI
IGAC
IGOS
ILAS
IMG
ImS
ISAMS
LEO
LIMS
LORE
MAHRSI
MAS
METOP
MIPAS
MLS
MSC
MOPITT
MOZAIC
NASA
NDSC
NOAA
Atmospheric Chemistry Experiment
Active Cavity Radiometer Irradiance Monitor
Advanced Global Atmospheric Gases Experiment
Atmospheric Radiation Experiment
Atmospheric Trace Molecule Spectrometer
Baseline Surface Radiation Network
Backscattered Ultra Violet
Committee on Earth Observation Satellites
Chlorofluorocarbons
Cryogenic Limb Array Etalon Spectrometer
Centre National d’Etudes Spatiales
Calibration for Ozone by Atmospheric Limb Acquisitions
Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere
Differential Optical Absorption Spectroscopy
ENVIronmental SATellite
Earth Observing System
Earth Radiation Budget Satellite
Earth Remote Sensing satellite
European Space Agency
EUropean Organisation for METeorological SATellites
Fourier Transform InfraRed
Global Atmosphere Watch
Global Climate Observing System
Geostationary Earth Orbit
Global Ozone Monitoring Experiment
Global Ozone Monitoring by Occultation of Stars
Global Positioning System - Meteorology
HALogen Occultation Experiment
Hydrogenated Chlorofluorocarbons
HIgh Resolution Dynamics Limb Sounder
HIgh Resolution infrared Sounder
High Resolution Doppler Interferometer
Infrared Atmospheric Sounding Interferometer
International Global Atmospheric Chemistry
Integrated Global Observing Strategy
Improved Limb Atmospheric Spectrometer
Interferometric Monitor of Greenhouse Gases
Imaging Spectrometer
Improved Stratospheic And Mesospheric Sounder
Low Earth Orbit
LImb Microwave Sounder
Limb Ozone Retrieval Experiment
Middle Atmosphere High Resolution Spectrographic Investigation
Millimetre wave Atmosphere Sounder
Meteorological Operational Satellite
Michelson Interferometer for Passive Atmospheric Sounding
Microwave Limb Sounder
Meteorological Service of Canada
Measurement of Pollution in the Troposphere
Measurement of Ozone by Airbus in service Aircraft
National Aeronautics and Space Administration
Network for the Detection of Stratospheric Change
National Oceanic and Atmospheric Administration
127
NOXA
NPOESS
ODIN
ODUS
OMI
OMPS
OMS
OSIRIS
PEM
POAM
PSC
RIS
SAGE
SAMS
SAM II
SAOZ
SBUV
SCIAMACHY
SMR
SMILES
SOLSE
SOLSTICE
SPARC
SSBUV
SUSIM
SVIRI
TES
TOA
TOMS
TOP
TOVS
UARS
UV
UVISI
WCRP
WINDII
WMO
Nitrogen OXides and ozone measurements along Air routes
National Polar Orbiting Environmental Satellite System
Swedish satellite to investigate the ozone layer
Ozone Dynamics Ultraviolet Spectrometer
Ozone Mapping Instrument
Ozone Mapping and Profiling Suite
Observations from the Middle Stratosphere
Optical Spectrograph and Infrared Imaging System
Particle Environment Monitor
Polar Ozone Aerosol Monitor
Polar Stratospheric Cloud
Retroreflector In Space
Stratospheric Aerosol and Gas Experiment
Stratospheric and Mesospheric Sounder
Stratospheric Aerosol Monitor
Systeme d'Analyse par Observations Zenthales
Solar Backscatter UltraViolet
Scanning Imaging Absorption Spectrometer for Atmospheric Cartography
SubMillimetre Radiometer
Superconducting subMIllimetre Limb Emission Sounder
Shuttle Ozone Limb Sounder Experiment
SOLar-STellar Irradiance Comparison Experiment
Stratospheric Processes And their Role in Climate
Shuttle Solar Backscatter Ultraviolet
Solar Ultraviolet Spectral Irradiance Monitor
Stationary Visible/InfraRed Imager
Troposphere Emission Spectrometer
Top Of Atmosphere
Total Ozone Mapping Spectrometer
Tropospheric Observation Project
TIROS Operational Vertical Sounder
Upper Atmosphere Research Satellite
UltraViolet
Ultraviolet and Visible Imagers and Spectrographic Imagers
World Climate Research Programme
WINd Imaging Interferometer
World Meteorological Organization
128
GLOBAL ATMOSPHERE WATCH
REPORT SERIES
1.
Final Report of the Expert Meeting on the Operation of Integrated Monitoring Programmes, Geneva,
2-5 September 1980
2.
Report of the Third Session of the GESAMP Working Group on the Interchange of Pollutants
Between the Atmosphere and the Oceans (INTERPOLL-III), Miami, USA, 27-31 October 1980
3.
Report of the Expert Meeting on the Assessment of the Meteorological Aspects of the First Phase of
EMEP, Shinfield Park, U.K., 30 March - 2 April 1981
4.
Summary Report on the Status of the WMO Background Air Pollution Monitoring Network as at April
1981
5.
Report of the WMO/UNEP/ICSU Meeting on Instruments, Standardization and Measurements
Techniques for Atmospheric CO2, Geneva, 8-11; September 1981
6.
Report of the Meeting of Experts on BAPMoN Station Operation, Geneva, 23-26 November, 1981
7.
Fourth Analysis on Reference Precipitation Samples by the Participating World Meteorological
Organization Laboratories by Robert L. Lampe and John C. Puzak, December 1981*
8.
Review of the Chemical Composition of Precipitation as Measured by the WMO BAPMoN by Prof.
Dr. Hans-Walter Georgii, February 1982
9.
An Assessment of BAPMoN Data Currently Available on the Concentration of CO2 in the Atmosphere
by M.R. Manning, February 1982
10.
Report of the Meeting of Experts on Meteorological Aspects of Long-range Transport of Pollutants,
Toronto, Canada, 30 November - 4 December 1981
11.
Summary Report on the Status of the WMO Background Air Pollution Monitoring Network as at May
1982
12.
Report on the Mount Kenya Baseline Station Feasibility Study edited by Dr. Russell C. Schnell
13.
Report of the Executive Committee Panel of Experts on Environmental Pollution, Fourth Session,
Geneva, 27 September - 1 October 1982
14.
Effects of Sulphur Compounds and Other Pollutants on Visibility by Dr. R.F. Pueschel, April 1983
15.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as Measured at BAPMoN Sites for the
Year 1981, May 1983
16.
Report of the Expert Meeting on Quality Assurance in BAPMoN, Research Triangle Park, North
Carolina, USA, 17-21 January 1983
17.
General Consideration and Examples of Data Evaluation and Quality Assurance Procedures
Applicable to BAPMoN Precipitation Chemistry Observations by Dr. Charles Hakkarinen, July 1983
18.
Summary Report on the Status of the WMO Background Air Pollution Monitoring Network as at May
1983
19.
Forecasting of Air Pollution with Emphasis on Research in the USSR by M.E. Berlyand, August 1983
20.
Extended Abstracts of Papers to be Presented at the WMO Technical Conference on Observation
and Measurement of Atmospheric Contaminants (TECOMAC), Vienna, 17-21 October 1983
21.
Fifth Analysis on Reference Precipitation Samples by the Participating World Meteorological
Organization Laboratories by Robert L. Lampe and William J. Mitchell, November 1983
129
22.
Report of the Fifth Session of the WMO Executive Council Panel of Experts on Environmental
Pollution, Garmisch-Partenkirchen, Federal Republic of Germany, 30 April - 4 May 1984 (TD No. 10)
23.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as Measured at BAPMoN Sites for the
Year 1982. November 1984 (TD No. 12)
24.
Final Report of the Expert Meeting on the Assessment of the Meteorological Aspects of the Second
Phase of EMEP, Friedrichshafen, Federal Republic of Germany, 7-10 December 1983. October
1984 (TD No. 11)
25.
Summary Report on the Status of the WMO Background Air Pollution Monitoring Network as at May
1984. November 1984 (TD No. 13)
26.
Sulphur and Nitrogen in Precipitation: An Attempt to Use BAPMoN and Other Data to Show Regional
and Global Distribution by Dr. C.C. Wallén. April 1986 (TD No. 103)
27.
Report on a Study of the Transport of Sahelian Particulate Matter Using Sunphotometer
Observations by Dr. Guillaume A. d'Almeida. July 1985 (TD No. 45)
28.
Report of the Meeting of Experts on the Eastern Atlantic and Mediterranean Transport Experiment
("EAMTEX"), Madrid and Salamanca, Spain, 6-8 November 1984
29.
Recommendations on Sunphotometer Measurements in BAPMoN Based on the Experience of a
Dust Transport Study in Africa by Dr. Guillaume A. d'Almeida. September 1985 (TD No. 67)
30.
Report of the Ad-hoc Consultation on Quality Assurance Procedures for Inclusion in the BAPMoN
Manual, Geneva, 29-31 May 1985
31.
Implications of Visibility Reduction by Man-Made Aerosols (Annex to No. 14) by R.M. Hoff and L.A.
Barrie. October 1985 (TD No. 59)
32.
Manual for BAPMoN Station Operators by E. Meszaros and D.M. Whelpdale. October 1985 (TD No.
66)
33.
Man and the Composition of the Atmosphere: BAPMoN - An international programme of national
needs, responsibility and benefits by R.F. Pueschel. 1986
34.
Practical Guide for Estimating Atmospheric Pollution Potential by Dr. L.E. Niemeyer. August 1986
(TD No. 134)
35.
Provisional Daily Atmospheric CO2 Concentrations as Measured at BAPMoN Sites for the Year 1983.
December 1985 (TD No. 77)
36.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1984. Volume I: Atmospheric Aerosol Optical Depth. October 1985 (TD No. 96)
37.
Air-Sea Interchange of Pollutants by R.A. Duce. September 1986 (TD No. 126)
38.
Summary Report on the Status of the WMO Background Air Pollution Monitoring Network as at 31
December 1985. September 1986 (TD No. 136)
39.
Report of the Third WMO Expert Meeting on Atmospheric Carbon Dioxide Measurement
Techniques, Lake Arrowhead, California, USA, 4-8 November 1985. October 1986
40.
Report of the Fourth Session of the CAS Working Group on Atmospheric Chemistry and Air
Pollution, Helsinki, Finland, 18-22 November 1985. January 1987
41.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1982, Volume II: Precipitation chemistry, continuous atmospheric carbon dioxide and suspended
particulate matter. June 1986 (TD No. 116)
42.
Scripps reference gas calibration system for carbon dioxide-in-air standards: revision of 1985 by
C.D. Keeling, P.R. Guenther and D.J. Moss. September 1986 (TD No. 125)
130
43.
Recent progress in sunphotometry (determination of the aerosol optical depth). November 1986
44.
Report of the Sixth Session of the WMO Executive Council Panel of Experts on Environmental
Pollution, Geneva, 5-9 May 1986. March 1987
45.
Proceedings of the International Symposium on Integrated Global Monitoring of the State of the
Biosphere (Volumes I-IV), Tashkent, USSR, 14-19 October 1985. December 1986 (TD No. 151)
46.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as Measured at BAPMoN Sites for the
Year 1984. December 1986 (TD No. 158)
47.
Procedures and Methods for Integrated Global Background Monitoring of Environmental Pollution by
F.Ya. Rovinsky, USSR and G.B. Wiersma, USA. August 1987 (TD No. 178)
48.
Meeting on the Assessment of the Meteorological Aspects of the Third Phase of EMEP IIASA,
Laxenburg, Austria, 30 March - 2 April 1987. February 1988
49.
Proceedings of the WMO Conference on Air Pollution Modelling and its Application (Volumes I-III),
Leningrad, USSR, 19-24 May 1986. November 1987 (TD No. 187)
50.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as Measured at BAPMoN Sites for the
Year 1985. December 1987 (TD No. 198)
51.
Report of the NBS/WMO Expert Meeting on Atmospheric CO2 Measurement Techniques,
Gaithersburg, USA, 15-17 June 1987. December 1987
52.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1985. Volume I: Atmospheric Aerosol Optical Depth. September 1987
53.
WMO Meeting of Experts on Strategy for the Monitoring of Suspended Particulate Matter in BAPMoN
- Reports and papers presented at the meeting, Xiamen, China, 13-17 October 1986. October 1988
54.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1983, Volume II: Precipitation chemistry, continuous atmospheric carbon dioxide and suspended
particulate matter (TD No. 283)
55.
Summary Report on the Status of the WMO Background Air Pollution Monitoring Network as at 31
December 1987 (TD No. 284)
56.
Report of the First Session of the Executive Council Panel of Experts/CAS Working Group on
Environmental Pollution and Atmospheric Chemistry, Hilo, Hawaii, 27-31 March 1988. June 1988
57.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1986, Volume I: Atmospheric Aerosol Optical Depth. July 1988
58.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as measured at BAPMoN sites for the
years 1986 and 1987 (TD No. 306)
59.
Extended Abstracts of Papers Presented at the Third International Conference on Analysis and
Evaluation of Atmospheric CO2 Data - Present and Past, Hinterzarten, Federal Republic of Germany,
16-20 October 1989 (TD No. 340)
60.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1984 and 1985, Volume II: Precipitation chemistry, continuous atmospheric carbon dioxide and
suspended particulate matter.
61.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
for 1987 and 1988, Volume I: Atmospheric Aerosol Optical Depth.
62.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as measured at BAPMoN sites for the
year 1988 (TD No. 355)
131
63.
Report of the Informal Session of the Executive Council Panel of Experts/CAS Working Group on
Environmental Pollution and Atmospheric Chemistry, Sofia, Bulgaria, 26 and 28 October 1989
64.
Report of the consultation to consider desirable locations and observational practices for BAPMoN
stations of global importance, Bermuda Research Station, 27-30 November 1989
65.
Report of the Meeting on the Assessment of the Meteorological Aspects of the Fourth Phase of
EMEP, Sofia, Bulgaria, 27 and 31 October 1989
66.
Summary Report on the Status of the WMO Global Atmosphere Watch Stations as at 31 December
1990 (TD No. 419)
67.
Report of the Meeting of Experts on Modelling of Continental, Hemispheric and Global Range
Transport, Transformation and Exchange Processes, Geneva, 5-7 November 1990
68.
Global Atmospheric Background Monitoring for Selected Environmental Parameters. BAPMoN Data
For 1989, Volume I: Atmospheric Aerosol Optical Depth
69.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as measured at Global Atmosphere
Watch (GAW)-BAPMoN sites for the year 1989 (TD No. 400)
Report of the Second Session of EC Panel of Experts/CAS Working Group on Environmental
Pollution and Atmospheric Chemistry, Santiago, Chile, 9-15 January 1991 (TD No. 633)
70.
71.
Report of the Consultation of Experts to Consider Desirable Observational Practices and Distribution
of GAW Regional Stations, Halkidiki, Greece, 9-13 April 1991 (TD No. 433)
72.
Integrated Background Monitoring of Environmental Pollution in Mid-Latitude Eurasia by Yu.A. Izrael
and F.Ya. Rovinsky, USSR (TD No. 434)
73.
Report of the Experts Meeting on Global Aerosol Data System (GADS), Hampton, Virginia, 11-12
September 1990 (TD No. 438)
74.
Report of the Experts Meeting on Aerosol Physics and Chemistry, Hampton, Virginia, 30-31 May
1991 (TD No. 439)
75.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as measured at Global Atmosphere
Watch (GAW)-BAPMoN sites for the year 1990 (TD No. 447)
76.
The International Global Aerosol Programme (IGAP) Plan: Overview (TD No. 445)
77.
Report of the WMO Meeting of Experts on Carbon Dioxide Concentration and Isotopic Measurement
Techniques, Lake Arrowhead, California, 14-19 October 1990
78.
Global Atmospheric Background Monitoring for Selected Environmental Parameters BAPMoN Data
for 1990, Volume I: Atmospheric Aerosol Optical Depth (TD No. 446)
79.
Report of the Meeting of Experts to Consider the Aerosol Component of GAW, Boulder, 16-19
December 1991 (TD No. 485)
80.
Report of the WMO Meeting of Experts on the Quality Assurance Plan for the GAW, GarmischPartenkirchen, Germany, 26-30 March 1992 (TD No. 513)
81.
Report of the Second Meeting of Experts to Assess the Response to and Atmospheric Effects of the
Kuwait Oil Fires, Geneva, Switzerland, 25-29 May 1992 (TD No. 512)
82.
Global Atmospheric Background Monitoring for Selected Environmental Parameters BAPMoN Data
for 1991, Volume I: Atmospheric Aerosol Optical Depth (TD No. 518)
83.
Report on the Global Precipitation Chemistry Programme of BAPMoN (TD No. 526)
84.
Provisional Daily Atmospheric Carbon Dioxide Concentrations as measured at GAW-BAPMoN sites
for the year 1991 (TD No. 543)
132
85.
Chemical Analysis of Precipitation for GAW: Laboratory Analytical Methods and Sample Collection
Standards by Dr Jaroslav Santroch (TD No. 550)
86.
The Global Atmosphere Watch Guide, 1993 (TD No. 553)
87.
Report of the Third Session of EC Panel/CAS Working Group on Environmental Pollution and
Atmospheric Chemistry, Geneva, 8-11 March 1993 (TD No. 555)
88.
Report of the Seventh WMO Meeting of Experts on Carbon Dioxide Concentration and Isotopic
Measurement Techniques, Rome, Italy, 7 - 10 September 1993, (edited by Graeme I. Pearman and
James T. Peterson) (TD No. 669)
89.
4th International Conference on CO2 (Carqueiranne, France, 13-17 September 1993) (TD No. 561)
90.
Global Atmospheric Background Monitoring for Selected Environmental Parameters GAW Data for
1992, Volume I: Atmospheric Aerosol Optical Depth (TD No. 562)
91.
Extended Abstracts of Papers Presented at the WMO Region VI Conference on the Measurement
and Modelling of Atmospheric Composition Changes Including Pollution Transport, Sofia, 4-8
October 1993 (TD No. 563)
92.
Report of the Second WMO Meeting of Experts on the Quality Assurance/Science Activity Centres of
the Global Atmosphere Watch, Garmisch-Partenkirchen, 7-11 December 1992 (TD No. 580)
93.
Report of the Third WMO Meeting of Experts on the Quality Assurance/Science Activity Centres of
the Global Atmosphere Watch, Garmisch-Partenkirchen, 5-9 July 1993 (TD No. 581)
94.
Report on the Measurements of Atmospheric Turbidity in BAPMoN (TD No. 603)
95.
Report of the WMO Meeting of Experts on UV-B Measurements, Data Quality and Standardization of
UV Indices, Les Diablerets, Switzerland, 25-28 July 1994 (TD No. 625)
96.
Global Atmospheric Background Monitoring for Selected Environmental Parameters WMO GAW
Data for 1993, Volume I: Atmospheric Aerosol Optical Depth
97.
Quality Assurance Project Plan (QAPjP) for Continuous Ground Based Ozone Measurements (TD
No. 634)
98.
Report of the WMO Meeting of Experts on Global Carbon Monoxide Measurements, Boulder, USA,
7-11 February 1994 (TD No. 645)
99.
Status of the WMO Global Atmosphere Watch Programme as at 31 December 1993 (TD No. 636)
100.
Report of the Workshop on UV-B for the Americas, Buenos Aires, Argentina, 22-26 August 1994
101.
Report of the WMO Workshop on the Measurement of Atmospheric Optical Depth and Turbidity,
Silver Spring, USA, 6-10 December 1993, (edited by Bruce Hicks) (TD No. 659)
102.
Report of the Workshop on Precipitation Chemistry Laboratory Techniques, Hradec Kralove, Czech
Republic, 17-21 October 1994 (TD No. 658)
103.
Report of the Meeting of Experts on the WMO World Data Centres, Toronto, Canada,
17-18 February 1995, (prepared by Edward Hare) (TD No. 679)
104.
Report of the Fourth WMO Meeting of Experts on the Quality Assurance/Science Activity Centres
(QA/SACs) of the Global Atmosphere Watch, jointly held with the First Meeting of the Coordinating
Committees of IGAC-GLONET and IGAC-ACE, Garmisch-Partenkirchen, Germany, 13-17 March
1995 (TD No. 689)
105.
Report of the Fourth Session of the EC Panel of Experts/CAS Working Group on Environmental
Pollution and Atmospheric Chemistry (Garmisch, Germany, 6-11 March 1995) (TD No. 718)
Report of the Global Acid Deposition Assessment (edited by D.M. Whelpdale and M-S. Kaiser) (TD
No. 777)
106.
133
107.
Extended Abstracts of Papers Presented at the WMO-IGAC Conference on the Measurement and
Assessment of Atmospheric Composition Change (Beijing, China, 9-14 October 1995) (TD No. 710)
108.
Report of the Tenth WMO International Comparison of Dobson Spectrophotometers (Arosa,
Switzerland, 24 July - 4 August 1995)
109.
Report of an Expert Consultation on 85Kr and 222Rn: Measurements, Effects and Applications
(Freiburg, Germany, 28-31 March 1995) (TD No. 733)
110.
Report of the WMO-NOAA Expert Meeting on GAW Data Acquisition and Archiving (Asheville, NC,
USA, 4-8 November 1995) (TD No. 755)
111.
Report of the WMO-BMBF Workshop on VOC Establishment of a “World Calibration/Instrument
Intercomparison Facility for VOC” to Serve the WMO Global Atmosphere Watch (GAW) Programme
(Garmisch-Partenkirchen, Germany, 17-21 December 1995) (TD No. 756)
112.
Report of the WMO/STUK Intercomparison of Erythemally-Weighted Solar UV Radiometers,
Spring/Summer 1995, Helsinki, Finland (TD No. 781)
113.
The Strategic Plan of the Global Atmosphere Watch (GAW) (TD No. 802)
114.
Report of the Fifth WMO Meeting of Experts on the Quality Assurance/Science Activity Centres
(QA/SACs) of the Global Atmosphere Watch, jointly held with the Second Meeting of the
Ed
Coordinating Committees of IGAC-GLONET and IGAC-ACE , Garmisch-Partenkirchen, Germany,
15-19 July 1996 (TD No. 787)
115.
Report of the Meeting of Experts on Atmospheric Urban Pollution and the Role of NMSs (Geneva, 711 October 1996) (TD No. 801)
116.
Expert Meeting on Chemistry of Aerosols, Clouds and Atmospheric Precipitation in the Former USSR
(Sankt Peterburg, Russian Federation, 13-15 November 1995)
117.
Report and Proceedings of the Workshop on the Assessment of EMEP Activities Concerning Heavy
Metals and Persistent Organic Pollutants and their Further Development (Moscow, Russian
Federation, 24-26 September 1996) (Volumes I and II) (TD No. 806)
118.
Report of the International Workshops on Ozone Observation in Asia and the Pacific Region
(IWOAP, IWOAP-II), (IWOAP, 27 February-26 March 1996 and IWOAP-II, 20 August-18 September
1996) (TD No. 827)
119.
Report on BoM/NOAA/WMO International Comparison of the Dobson Spectrophotometers (Perth
Airport, Perth, Australia, 3-14 February 1997), (prepared by Robert Evans and James Easson) (TD
No. 828)
120.
WMO-UMAP Workshop on Broad-Band UV Radiometers (Garmisch-Partenkirchen, Germany, 22-23
April 1996) (TD No. 894)
121.
Report of the Eighth WMO Meeting of Experts on Carbon Dioxide Concentration and Isotopic
Measurement Techniques (prepared by Thomas Conway) (Boulder, CO, 6-11 July 1995) (TD No.
821)
122
Report of Passive Samplers for Atmospheric Chemistry Measurements and their Role in GAW
(prepared by Greg Carmichael) (TD No. 829)
123
Report of WMO Meeting of Experts on GAW Regional Network in RA VI, Budapest, Hungary, 5-9
May 1997
124
Fifth Session of the EC Panel of Experts/CAS Working Group on Environmental Pollution and
Atmospheric Chemistry, (Geneva, Switzerland, 7-10 April 1997) (TD No. 898)
125.
Instruments to Measure Solar Ultraviolet Radiation, Part 1: Spectral Instruments (lead author G.
Seckmeyer) (TD No. 1066)
134
126.
Guidelines for Site Quality Control of UV Monitoring (lead author A.R. Webb) (TD No. 884)
127.
Report of the WMO-WHO Meeting of Experts on Standardization of UV Indices and their
Dissemination to the Public (Les Diablerets, Switzerland, 21-25 July 1997) (TD No. 921)
128.
The Fourth Biennial WMO Consultation on Brewer Ozone and UV Spectrophotometer Operation,
Calibration and Data Reporting, (Rome, Italy, 22-25 September 1996) (TD No. 918)
129.
Guidelines for Atmospheric Trace Gas Data Management (Ken Masarie and Pieter Tans), 1998 (TD
No. 907)
130.
Jülich Ozone Sonde Intercomparison Experiment (JOSIE, 5 February to 8 March 1996), (H.G.J. Smit
and D. Kley) (TD No. 926)
131.
WMO Workshop on Regional Transboundary Smoke and Haze in Southeast Asia (Singapore, 2-5
June 1998) (Gregory R. Carmichael). Two volumes
132.
Report of the Ninth WMO Meeting of Experts on Carbon Dioxide Concentration and Related Tracer
Measurement Techniques (Edited by Roger Francey), (Aspendale, Vic., Australia)
133.
Workshop on Advanced Statistical Methods and their Application to Air Quality Data Sets (Helsinki,
14-18 September 1998) (TD No.956)
134.
Guide on Sampling and Analysis Techniques for Chemical Constituents and Physical Properties in
Air and Precipitation as Applied at Stations of the Global Atmosphere Watch.
Carbon Dioxide
135.
Sixth Session of the EC Panel of Experts/CAS Working Group on Environmental Pollution and
Atmospheric Chemistry (Zurich, Switzerland, 8-11 March 1999) (WMO TD No.1002)
136.
WMO/EMEP/UNEP Workshop on Modelling of Atmospheric Transport and Deposition of Persistent
Organic Pollutants and Heavy Metals (Geneva, Switzerland, 16-19 November 1999) (Volumes I and
II) (TD No. 1008)
137.
WMO RA-II/RA-V GAW Urban Research Meteorology and Environment (GURME) Workshop
(Beijing, China, 1-4 November 1999) (WMO-TD. 1014)
138.
Reports on WMO International Comparisons of Dobson Spectrophotometers, Parts I – Arosa,
Switzerland, 19-31 July 1999, Part II – Buenos Aires, Argentina (29 Nov. – 12 Dec. 1999 and Part III –
Pretoria, South Africa (18 March – 10 April 2000).
139.
The Fifth Biennial WMO Consultation on Brewer Ozone and UV Spectrophotometer Operation,
Calibration and Data Reporting (Halkidiki, Greece, September 1998)(WMO TD No. 1019).
140.
WMO/CEOS Report on a Strategy for Integrating Satellite and Ground-based Observations of Ozone
(WMO TD No. 1046).
135