GSICS VIS/NIR subgroup report
David Doelling (sub-lead-facilitator), and all
other VIS/NIR members
GSICS Annual Meeting, Darmstadt,
Germany, March 24-28, 2014
NASA Langley Research Center / Atmospheric Sciences
Outline
• An example of how calibration impacts retrievals
• Calibration accuracy through time
• Reference sensor and traceability to future
instruments and methods
• Comparison of visible calibration techniques
• Coordination of GPRC for common short and long
term goals
• Proposed forward progress
• This years goals
NASA Langley Research Center / Atmospheric Sciences
CERES fluxes
• CERES measures the Earth’s broadband shortwave and
longwave fluxes
• MODIS cloud properties aid in converting measured CERES
radiances to fluxes, since the SW BRDF is scene based,
– absolute calibration is tied to CERES instrument
– The current CERES Edition 3 products uses a combination of
MODIS C4 and C5 radiances
• CERES users try to correlate cloud/aerosol/land retrievals with
CERES fluxes to evaluate climate change
MODIS C5 DCC stability
NASA Langley Research Center / Atmospheric Sciences
Wu et al. 2013
The effect of MODIS band 1 calibration on
retrieved optical depth
•
Compute global monthly mean optical depth from MODIS pixel level
retrievals
–
•
A 2.5% MODIS calibration drift has resulted in a ~8% decrease in cloud
optical depth
–
–
•
+0.4
Deseasonalize to determine trend over time
Which may be falsely interpreted as climate change
Collection 6 stable to 1%/decade
GSICS calibration goal is to improve and harmonize cloud/aerosol/land
retrievals
+0.4
Terra-MODIS C5
+0.0
Aqua-MODIS C5
+0.0
http://ceres.larc.nasa.gov/order_data.php
-0.4 2000
2012
2005
-0.4 2002
NASA
Langley Research Center
/ Atmospheric 2007
Sciences
2012
VIS/NIR Calibration Milestones
• 1980 ISCCP 5% calibration accuracy
– “The Earth is more stable than your sensor” Bill Rossow
• 1995 to 2000 First solar diffusers for VIS bands
– ERS2-ATSR2, TRMM-VIRS, Terra-MODIS
• 2006 MODIS band 1 C5 calibration 2%/decade trend
• 2010 MODIS band 1 C6 calibration 1%/decade trend
• 2014 Predicted VIIRS stability
– Desert Calibration stability 1%/decade
– DCC calibration stability 0.5%/decade (Bhatt et al. 2014)
• Predicted anthropogenic SW forcing, 0.3%/decade
• 2025 CLARREO/TRUTHS absolute calibration accuracy 0.3% 2K
• Solar Cycle amplitude 0.1%/11years
NASA Langley Research Center / Atmospheric Sciences
Reference Calibration
•
•
Reference Instrument or reference calibration tied to radiative transfer
(RT) predicted radiances?
How traceable are the radiative transfer (RT) radiances
– Dependent on RT method and inputs, how traceable in time are they?
– The inputs were based on MODIS cloud properties, which are tied then to
the MODIS calibration
•
Either way we agree on reference instrument for traceability
Okuyama. GSICS 2009 web meeting
RT based
Reference Instrument based
NASA Langley Research Center / Atmospheric Sciences
VIS/NIR reference instrument
• Ideal traceable on orbit calibration hyper-spectral
instrument such as the future CLARREO/TRUTHS
– If the calibration is traceable on orbit you need no overlap
between successive instruments
– You can monitor change with an equivalent instrument years in
the future
• Now given todays instruments
– The data must be freely available, user friendly, and widely
used, very familiar with the community (retrievals well
documented)
– Must be a well characterized sensor and stability referenced
through a solar diffuser and/or moon
• Navigation, instrument radiometric noise, polarization knowledge
– Must be traceable (inter-calibrated) with future instruments
NASA Langley Research Center / Atmospheric Sciences
Traceable inter-calibration
• if the VIS reference instruments can be faithfully intercalibrated, then the absolute calibration of a future
instrument can be reference back in time
– Eventually future instruments will have excellent absolute and
SI traceable calibration
• Factors that increase the confidence of inter-calibration
– Overlapping successive or follow on operational instruments,
such as NPP/JPSS-VIIRS, Metop-SG-MetImage
– Length of overlap period
– Similar spectral channels, known SRFs
– Similar (equator crossing time) well maintained (non drifting
LEO) orbits, to observe entire dynamic range over all earth
targets
NASA Langley Research Center / Atmospheric Sciences
Reference Instrument
• The reference instrument absolute calibration is secondary as
long as the calibration is very stable and well characterized
• However it is important that the absolute calibration can be
traced to the reference instrument for all contemporary
operational visible calibration methods
– This allows the comparison of calibration methods
– This allows uniform cloud/aerosol/land retrievals over multiple
platforms both spatially and temporally
– This allows future calibration enhancements to improve the entire
record
• GSICS goal is to verify the operational instrument stability so
that the reference instrument calibration can be transferred
effectively
NASA Langley Research Center / Atmospheric Sciences
Visible Calibration Methods
• No traceable reference VIS hyper-spectral instrument is available,
therefor a multiple calibration approach is taken
– Agreement among methods validates the resulting calibration
– Each method has its advantages and disadvantages
Hewison, GSICS annual meeting 2009
NASA Langley Research Center / Atmospheric Sciences
VIS calibration technique comparison
(not comprehensive)
GEO Method
Stability at
TOA
SBAF
Traceable to
reference
Sampling
Historical
application
Lunar
•Geological
variability
• Earth view
optics?
ROLO model
at
MODIS/VIIRS
phase angles
•Monthly
•Long phase
and libration
period
Dependent on
sampling
DCC
•0.5%/decade
(VIIRS)
• tropopause
Nearly flat
spectrally
•DCC
raymatch
•Domain
mean
Large sample
collective
method
Reference
calibration
difficult
Rayliegh
RT depends
Wind speed
Chlorophyll
RT at surface,
good for
interband
Reference/RT
compare
Use
coincident
MODIS .8µm
Need 0.8µm
reflectivity
Desert
1.0%/decade
(VIIRS)
• surface
Need
observed
hyper-spectral
SADE with
atmosphere
Not available
over all GEO
domains
Long term
invariance not
known
Liquid Water
Clouds
Direct
compare
RT model
MODIS cloud
properties
Dependent on
reference
orbit
Need
coincident
reference obs
Ray-match
Direct
compare
Needed for
clear-sky and
low clouds
MODIS
radiances
Dependent on
reference
orbit
Need
coincident
reference obs
NASA Langley Research Center / Atmospheric Sciences
GSICS GEO VIS ATBDs
• ATBD is the first step to implement VIS method within GSICS
• VIS ATBDs in GSICS library, effort started in 2011
–
–
–
–
–
–
–
–
Liquid Water Clouds (JMA) – Arata Okuyama
Liquid Water Clouds (SNU) B.J. Sohn
Lunar (NOAA) – Fred Wu
Stellar (NOAA) – Fred Wu
DCC (NASA) – David Doelling
DCC (SNU) – B.J. Sohn
(MODIS/GEO) Ray-matching (NASA) – David Doelling
Combining Methods (EUMETSAT) – Tim Hewison
• VIS ATBDs TBD
–
–
–
–
Rayleigh (CNES) draft status? - Bertrand Fougnie
Desert (CNES) – Patrice Henry
Desert (EUMETSAT) – Sebastien Wagner
Sunglint (NOAA) Andy Heidinger
NASA Langley Research Center / Atmospheric Sciences
Implementation of VIS methods
Fred Wu, GSICS web meeting 2009
• Common VIS method goals
– Common effort
– Common product (requires more GPRC commitment)
– Common algorithm (creates more uniformity)
• Common VIS calibration product goals
– Quantify the bias
– Correct the bias (benefits the retrieval community)
– Diagnose the bias
• Common VIS record goals
– Common algorithm during reference sensor record
– Common algorithm for reference sensor and historical record
• Common GPRC goals
– Best to coordinate various GPRC goals and commitments
NASA Langley Research Center / Atmospheric Sciences
VIS calibration method product timeline
• Calibration method timeline
Fangfang Yu, GPPA workflow 2013
– Year 1: Agree on calibration approach from existing methods or a
combined approach
– Year 2: GPRC’s implement common approach – have verification
dataset to ensure uniform implementation
– Year 3: GPRC’s deliver submission/demonstration phase products
to GSICS – formatted, documented, peer reviewed, user tested
– Year 4: GPRC’s deliver pre-operational/operation phase products,
version control, made public, accepted
• Can method implementations be staggered to accelerate
products?
2012
2013
2014
2015
2016
2017
2018
DCC
Lunar
Rayleigh?
NASA Langley Research Center / Atmospheric Sciences
VIS calibration product timeline
• Do we spend time to modify method for historical
instruments?
• Do we spend time to modify method for LEO
instruments?
• How will these efforts be redirected when the next
generation GEOs are launched in a few years?
– These will have their calibration stability tied to solar views
• The methodology will be straight forward once either
CLARREO or TRUTHS hyper-spectral radiances are
available for calibration
– Probably at least 10 years from now
NASA Langley Research Center / Atmospheric Sciences
Goals/Discussion for this year
• DCC
– Agree on methodology (Version 1)
– Product, bias monitoring and path to demonstration product
– Determine DCC reference calibration tied to MODIS and SBAF
• Lunar
– Agree on methodology that applies uniformly to all
– Reference ROLO with MODIS at MODIS phase angles
– Improve ROLO with Plaiedes?
• Rayleigh
– Requires 0.86µm channel, use coincident MODIS 0.86µm?
– Prepare for next generation GEO
• Explore next technique
– Desert (IVOS), liquid water, combining methods
NASA Langley Research Center / Atmospheric Sciences