1. Strategy for calibration references
Special Issue of the IEEE TGRS on “Inter-Calibration of Satellite Instruments”:
Special Issue of the IEEE TGRS on “Inter-Calibration of Satellite Instruments”:
27 December 2018
Strategy for calibration references
Tim Hewison
(EUMETSAT) (GRWG Chair)

2. Overview Update on Prime GSICS Corrections
For information
How to select inter-calibration reference instruments
Improving the Moon
As a calibration reference
A case for international collaboration
Recommendation needed!

3. Overview Update on Prime GSICS Corrections
For information
How to select inter-calibration reference instruments
Improving the Moon
As a calibration reference
A case for international collaboration
Recommendation needed!

4. New Prime GSICS Corrections
Define one Primary GSICS Reference
For each spectral band/application
By consensus agreement within GSICS
Use others as Transfer References
Blend corrections from all references
After modifying Corrections to Primary GSICS Reference
Ensures long-term continuity
Without calibration jumps
Ensures Traceability
back to single Primary Reference
Simplifies users’ implementation
Could also blend multiple methods?

5. Correcting the Corrections and Blending References
Reference-1 (Primary)
Monitored Instrument
Reference-2
(Secondary)
GSICS Correction, g1 Mon1
GSICS Correction, g2 Mon2 -
Derived by GSICS
Delta
Correction, g1/2
21 +
Modified
Correction, g2,1/2
Mon 21 g̅
Prime GSICS Correction, g0 Mon1
MonRef1
Applied
by User

6. Users’ Application of Prime GSICS Correction
Monitored Instrument
Prime GSICS Correction, g0 Mon1
MonRef1

7. Overview Update on Prime GSICS Corrections
For information
How to select inter-calibration reference instruments
Improving the Moon
As a calibration reference
A case for international collaboration
Recommendation needed!

8. Reference Instrument Selection/Migration
GSICS products need an inter-calibration reference
Inter-calibration  Reference is one instrument
Other instruments may be used as transfer references
We need a way to select the reference
From a list of candidates
First question should be: “Is it suitable at all?”
Does it meet minimum threshold requirements (availability, coverage, ...)
Started asking “How good is it as a Reference?”
Impact on overall uncertainty
Score scheme

9. Example for SEVIRI-IASI IR
Scoring Scheme for GSICS Re-Analysis Correction for SEVIRI IR Channels
Threshold
Saturation
MetopA/IASI
Unit
Min
Max
Weight
OK?
Perfect
Score
Date Range
Year
2013
2006
2030 90
2007
2020
Pass
54%
48.8
Geographic Coverage: Lat
deg
-10 10
-90 2
100%
2.0
Geographic Coverage: Lon
-180
180
Dynamic Range K
270
300
330 5
310
87%
4.3
Spectral Range
cm-1
746
2564
650
2800
645
2760
98%
9.8
Geometric Range: VZA 15
0.5 55
61%
1.2
Geometric Range: VAA
0.0
Geometric Range: SZA
Geometric Range: SAA
Geometric Range: Pol
Diurnal Coverage hr 9 12 20
7.8
11.2
28%
5.6
Field of View km 3 1
1.0
Number of obs/day /d
Number of Collocations
10000
30000
5.0
Geolocation accuracy
0.1
3.3 3%
0.3
Polarisation knowledge
Radiometric Stability
K/yr
0.001
0.05 2%
0.2
Orbital Stability
hr/yr
Radiometric Noise
0.15
67%
0.7
Uncertainty from SBAF
0.01
0.008
20.0
Spectral Resolution
100
0.25
Spectral Stability
cm-1/yr
2E-06
SBAF Uncertainty 1%
Absolute Calibration Acc
Inter-channel calibration
Data Availability
Documentation
Community adoption
Traceability
Fail
Total
200.0
96%
51%
101.1
Example for SEVIRI-IASI IR
OneDrive Spreadsheet
All values for illustration only
And subject to change
Some variables more important for different inter-cal products
Timeliness important for NRTC
Date range critical for Archive Re-Calibration
Assumed time-stamp is correct!
Scheme needs road testing with other References

10. Expanding WMO OSCAR Capabilities
Observing Systems Capability Analysis and Review Tool
Adding Landing Pages with links to:
Instrument Specifications, Calibration Events, Data Outages, Instrument Monitoring
WMO expanding OSCAR
automatically assess instruments’ capability to address requirements
Based on pre-defined Expert Rules
Could be used to assess GSICS References
Action: Manik to interact with Jérôme to push forward the development of the expert system as a tool to select inter-calibration reference instruments 

11. Instrument view
GSICS - New Delhi- OSCAR 16-20/03/2015

12. Overview Update on Prime GSICS Corrections
For information
How to select inter-calibration reference instruments
Improving the Moon
As a calibration reference
A case for international collaboration
Recommendation needed!

13. Lunar Calibration Workshop
Organised by EUMETSAT in collaboration with USGS, CNES, NASA
Almost 30 people from 14 different agencies and departments attending (physically or remotely)  GSICS / CEOS-IVOS
All participants used GSICS Implementation of ROLO model (GIRO) developed at EUMETSAT in collaboration with T. Stone (USGS)
To develop inter-calibration algorithm, need accurate oversampling factors  difficulty encountered by all participants
Major outcomes:
the calibration community agreed the GIRO to be the international reference for lunar calibration, traceable to the ROLO model from USGS
Establishment of a Lunar Observation Database
Recommend investigating possible funding to establish infrastructure to traceable lunar observations
Participants in the Lunar Calibration Workshop
Hosted at EUMETSAT, 1-4 Dec 2014
A GIRO usage policy and a data policy will be defined in collaboration with the participants
USGS expected to have a new version of the ROLO by the end of 2015  updated GIRO by mid-2016
All participants agreed about the need to organise another Lunar Calibration Workshop (~1 year time)

14. Number of Obs (GSICS dataset)
Instruments
Team
Satellite
Sensor
G/L
Dates
Number of Obs (GSICS dataset)
Phase angle range (°)
CMA
FY-3C
MERSI
LEO 9
[43 57]
FY-2D
VISSR
GEO
FY-2E
FY-2F
JMA
MTSAT-2
IMAGER 62
[-138,147]
GMS5 50
[-94,96]
Himawari-8
AHI
2014- -
EUMETSAT
MSG1
SEVIRI
380/43
[-150,152]
MSG2
312/54
[-147,150]
MSG3
45/7
[-144,143]
MET7
MVIRI
128
[-147,144]
CNES
Pleiades-1A
PHR
2012 10
[+/-40]
Pleiades-1B
NASA-MODIS
Terra
MODIS
136
[54,56]
Aqua
117
[-54,-56]
NASA-VIIRS
NPP
VIIRS 20
[50,52]
NASA-OBPG
SeaStar
SeaWiFS
204
(<10 , [27-66])
NASA/USGS
Landsat-8
OLI 3
[-7]
NASA
OCO-2
OCO
2014
NOAA-STAR 19
[-52,-50]
NOAA
GOES-10 33
[-66, 81]
GOES-11
[-62, 57]
GOES-12 49
[-83, 66]
GOES-13
2006 11
GOES-15 28
[-52, 69]
VITO
Proba-V
VGT-P 25
KMA
COMS MI 60
AIST
ASTER 1
-27.7
ISRO
OceanSat2
OCM-2 2
INSAT-3D
Instruments with lunar observation capabilities, with the minimum number of Moon observations provided to the GSICS Lunar Observation Dataset (GLOD) - more observations may be available.

15. Examples of Moon observations from participating instruments

16. According to OSCAR (WMO)
Courtesy B. Fougnie, CNES
LEO (CWL)
GEO (band)
Landsat-8
According to OSCAR (WMO)

17. Courtesy B. Fougnie, CNES
LEO
GEO
Landsat-8

18. Courtesy B. Fougnie, CNES
LEO
GEO
Landsat-8

19. Improving the Moon (as a reference)
Where we are:
GSICS Implementation of ROLO (“GIRO”) v1.0.0 now available, validated against ROLO
Starting to compile GSICS Lunar Observations Database (“GLOD”)
Already found significant dependencies in relative biases of Observed-GIRO irradiances
But still good enough to inter-calibrate 0.6m band to <1% uncertainty (NIR not so good)
Absolute calibration using GIRO limited to 5-10% by original ROLO dataset
Short-term plan:
Develop inter-calibration algorithm
Integrate results with DCCs in new GSICS products
Continue to expand GSICS Lunar Observations Database (“GLOD”)
Form community consensus on absolute scale of GIRO
Long-term plan:
Tie GIRO to SI-traceable standards
Ideally through long-term campaign of new hyperspectral lunar observations

20. Proposal for activities to address inter-calibration using the Moon
In EUMETSAT’s proposal, points to be addressed:
Estimating the over-sampling factor
Drift correction
Estimation of the SBAFs from GIRO and verification of the results.
Establishing an absolute scale for lunar calibration
Medium and long term activities on lunar calibration

21. ROLO/GIRO and absolute calibration
KNOWN DEFICIENCIES OF THE CURRENT REFERENCE
SI traceability
Absolute scale uncertainty (5 – 10 % uncertainty in absolute irradiance scale)
Residual geometry dependencies
Multi-band spectral coverage
ESTABLISHING THE REQUIREMENTS
Defining potential improvements and requirements on user applications
Independent method to verify that operational visible calibration meets requirements 
Support climate applications and past instruments (e.g. no onboard calibration available)
GOAL
Getting absolute uncertainties to under ~1%
Surface stability + predictability of the Moon’s brightness = lunar reflectance model valid for all times
Level of accuracy of 0.5% is achievable
WHAT IS NEEDED?
Need for a new lunar measurement program (= many years of observations, to characterize the variations of the lunar brightness with phase and librations)
Minimum 3 years to capture the libration dependence within the bounds of its relative effect (ROLO operated for more than 8 years)
Traceable high-spectral resolution observations over several years with specific measurements to validate the atmospheric correction.
FUNDING: Currently under investigation (inter-agency [international] collaboration?)

22. E. Medium and long term activities on lunar calibration
Investigate the possibility to participate to an international consortium to fund dedicated measurement campaigns.
Review planned activities in this area:
CMA: Obtained funding for new ground-based observations from CAS
CNES?
ESA: interest in contributing but no existing mechanism for such an international funding. Further investigations needed.
EUMETSAT: no existing mechanism for international funding but possibility still under investigation. Science Working Group defines users requirements.
ISRO? IMD?
JMA: no possibility for funding
KMA?
NASA: Proposed ARCSTONE mission for Earth Venture funding
NOAA?
CEOS/IVOS members: AIST, JAXA, KIOST, VITO?

23. Conclusions Advice of CEOS-WGCV for GSICS: Requirements:
Develop inter-calibration using current GIRO as soon as possible
Support SI-traceable lunar observations to tie ROLO to absolute scale
Encourage independent reproduction of ROLO observations
Requirements:
System suitable for operational application (source code)
Globally accessible common lunar irradiance model
Recommendation is sought from GSICS/CGMS:
How to establish international cooperation to establish, operate and process
A campaign of new lunar observations over full range of conditions (>3yr)
Covering full reflected solar band at high spectral resolution (hyperspectral)
Directly traceable to SI standards

24. 27/12/2018
Thank You 24