GRWG Report
Tim Hewison
1 November 2012
Outline
• Status Updates – For Information only
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GEO-LEO IR
GEO Solar
Lunar
Archive Re-Calibration Products
IEEE TGARS Special Issue
Instrument Event Logs
GRUAN
• Issues for Exec Panel decisions
– Statement on GSICS-GRUAN interaction
– Chairing GRWG
– Procedure for GSICS Membership
GEO-LEO IR (1)
• Most of the GSICS Corrections for the infrared channels of current
geostationary imagers are now in demonstration mode.
• NOAA and EUMETSAT hope to have the products for the GOES
and MSG series promoted to pre-operational status during Fall
2012. While these are mature products, they are subject to
limitations - in particular the range of time over which they are valid.
• Many GEOs suffer from diurnal variations in the calibration - and in
particular during the period around local midnight. These are being
addressed by the development of a method to transfer the intercalibration reference over more of the diurnal cycle, initially using
Aqua/AIRS to transfer the calibration from Metop-A/IASI.
GEO-LEO IR (2)
• GRWG have also been preparing a framework to allow the
transfer our inter-calibration reference instrument from MetopA/IASI to Metop-B/IASI by calculating "Delta Corrections",
based on double-differences of the GSICS Corrections
calculated using each independently.
• This is complemented by CNES' plans to perform
comparisons of Metop-A/IASI and Metop-B/IASI by a number
of different methods to account for the unavailability of
simultaneous collocated observations due to the orbital
configuration.
GEO-LEO IR (3)
• The common format developed for the GSICS Corrections by
GDWG have allowed a new plotting tool to be developed to
generate GSICS Bias Monitoring, by reading the contents of the
netCDF files directly from the GSICS servers.
• The same tool can be used to generate and compare intercalibration products from different instruments generated by
different GPRCs.
• This has required extensive interaction with GDWG to define
additional attributes in the netCDF files to allow the conversion of
the results into brightness temperatures, which are more
meaningful to the users than the radiances used in the calculation.
GEO Solar (1)
• Development work has continued to focus on inter-calibration
for the channels of the current geostationary imagers in the
reflected solar band.
• Outline ATBD was produced by Dave Doelling (NASA),
– based on comparing statistical distributions of the reflectances of Deep
Convective Clouds (DCCs) observed from the GEO imagers
– and MODIS, as an inter-calibration reference instrument.
• EUMETSAT are currently implementing this algorithm.
• NASA are preparing centralised processing of MODIS data
– to generate statistics of the reference instrument,
– which will be commonly used for all GEO imagers.
GEO Solar (2)
• Members of GRWG have also been involved in a review of
the Saharan desert sites currently used as calibration
reference targets.
• The spatial, temporal and spectral variability of different sites
has been analysed to quantify the uncertainties associated
with their use, and potentially to reduce this by refining the
site selections.
– This has included a dedicated workshop on the Libya #4 site,
coordinated by IVOS.
• GRWG to investigate potential use of GOME/SCIAMACHY
hyperspectral observations to validate models and/or as an
inter-calibration reference for solar band channels.
Lunar
• Several GRWG members have been investigating the Moon
as a calibration transfer reference for Geostationary imagers
channels in the reflected solar band
– although it is also applicable to LEO instruments.
• GRWG has encouraged USGS to set up an online facility to
provide irradiance predictions from their ROLO model
– customised for specific observations of various instruments,
– accounting for their viewing geometry and spectral response.
• GRWG has encouraged NIST to consider tying the current
lunar irradiance models to SI-traceable standards,
– Would allow lunar observations to provide useful absolute calibration
– (at present their application is practically limited to detecting calibration
trends and inter-channel differences).
Archive Re-Calibration
• GRWG identified need for new class of inter-calibration product:
to provide a consistent calibration for whole datasets from different satellite
instruments
– to generate Fundamental Climate Data Records.
• These Archive Re-Calibration products will complement existing products,
– which have mostly focused on near real-time applications.
• Examples now in demonstration mode:
– PATMOS-x product for AVHRR
– (A)MSU inter-calibration products, developed at NOAA
• EUMETSAT are also developing inter-calibration products for the Meteosat
archive, using various HIRS instruments as references.
IEEE TGARS Special Issue
• Special issue of IEEE Transactions on Geoscience and
Remote Sensing on the Inter-Calibration of Satellite
Instruments
– proposed jointly by GSICS and IVOS
– including four guest editors from GRWG.
• When published, in early 2013, this special issue will provide
a valuable reference to the inter-calibration community,
– bringing together a large collection of papers focusing on this topic.
• These include many from GRWG authors,
– covering the generation, validation and analysis
– of various GSICS products,
– as well as an extensive overview of inter-calibration techniques.
• Papers can be made Open Access – at a price (US$3000)
EUMETSAT activities on Calibration Event Logging
Achievements to date:
1. Set-up of an internal EUMETSAT Working Group on Calibration Event Logging after a
recommendation from CGMS and GSICS
 Focus = log any event capable of affecting data quality and calibration
2. Assessment of the current logging systems available at EUMETSAT
3. Draft of the concept for a calibration event logging system  database providing
information on:
• Mission
GSICS Research & Data Working Group to
• Irregular Events
provide advice and support for standard
• Processing Events
definitions and reporting
• Data Outages
4. Contribution to be presented at the CGMS meeting 40 (CGMS-40 EUM-WP-09)
Next steps forward:
1. Ask CGMS + GSICS partners to review of the proposed concept
2. Formulation and formalization of the user requirements
3. Regular reporting to the internal EUMETSAT Climate Monitoring Coordination Group
4. Incorporate feedback from internal + external users into the database
5. Iteration through GSICS with external partners to refine the system before deployment
Slide:
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GRUAN (GCOS Reference Upper Air Network)
Representation at GRUAN Expansion Workshop
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Participation in group writing white paper on sat cal/val
Emphasis on quality, not quantity of radiosondes
Launches timed for satellite overpasses
Can select sites where these are synoptic hours (0z, 12z)
Real-time evaluation of representativeness errors
– Based on observed variability in space & time
• 3-way interaction for validation of L2 products
– e.g. UTH (w/ SCOPE-CM/CMSAF)
Proposal by GSICS-EP-13
for a Statement on GSICS-GRUAN interaction (1)
Why would it be good to have such a statement?
 the relationship between GSICS and GRUAN is being
addressed at various meetings. And generally speaking,
perception and perspectives are not aligned.
 therefore a general statement reflecting the standpoint of
GSICS could be helpful for reference in future discussions.
Proposal by GSICS-EP-13
for a Statement on GSICS-GRUAN interaction (2)
Proposal for a formulation:
The GSICS Executive Panel sees potential for mutual benefits of
GRUAN and GSICS activities. The EP wishes to stress that
the benefit is clearly mutual. Therefore coordinated activities
in specific areas are recommended (an example is presented
on the following slide).
Proposal by GSICS-EP-13
for a Statement on GSICS-GRUAN interaction (3)
Example for mutual benefit:
GRUAN measurements could provide improved input data for radiative
transfer simulations of the high resolution radiance spectra at the top-ofthe-atmosphere , those spectra can be compared with hyperspectral
satellite measurements (e.g. AIRS and IASI).
• Differences between measured and calculated spectra should in principle
be the same for all GRUAN stations under the assumption that the
measurements are stable (this is a very valid assumption) and that
GRUAN stations have the same bias errors (this is to be shown)
• Thus, GSICS would provide via the hyperspectral satellite measurements
a ‘travelling reference standard’ for GRUAN stations.
• It is understood that the realisation of such benefits requires coordination
between GSICS and GRUAN, for instance the launching of radiosondes
sufficiently close to a satellite overpass.
Other Issues: Chairing GRWG
GRWG Chairing - Suggestion:
• Identify specific roles to be covered by vice-chairs of GRWG
e.g. Grouped by Product Class
• Development of GSICS Products for Solar Band GEOs
• LEO-LEO products
• Developing methods for Archive Re-Calibration
Or grouped by spectral band:
• Thermal Infrared
• Reflected Solar Band (incl. Ocean Colour?)
• Microwave
Other Issues: Expanding Membership
• Expansion of GSICS
– from a GRWG perspective the main issue is additional need for
resources to keep up with the additional needs/expectations and the
science development
– GRWG asks the GSICS EP to provide firmer guidance
• There are already some firm rules/constraints for membership
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Adherence to scope of GSICS,
Commitment for free & open exchange,
Developing inter-calibration products for their instruments
tying to GSICS standards…
• Procedure for Membership application