1. Sébastien Wagner, Tim Hewison In collaboration with D. Doelling (NASA)
Inter-calibration of the SEVIRI VIS06 band against MODIS Aqua, using Deep Convective Clouds as transfer targets
Sébastien Wagner, Tim Hewison
In collaboration with D. Doelling (NASA)
Contact:

2. Outline GSICS activities for solar reflective bands at EUMETSAT
Current calibration system (for the solar reflective bands)
Inter-calibration with MODIS using DCCs
Main steps
Some results
Conclusions and future work

3. Outline GSICS activities for solar reflective bands at EUMETSAT
Current calibration system (for the solar reflective bands)
Inter-calibration with MODIS using DCCs
Main steps
Some results
Conclusions and future work

4. GSICS current activities for solar reflective bands at EUMETSAT
Users
Level 1b/c Data
(Radiances)
GOS
Corrections
Statement of Needs
SCOPE CM
NWP centres
Developers of Lev2/3 products
...
Inter-calibration with MODIS using DCCs
Inter-calibration with ROLO using the Moon
Absolute calibration
To be discussed !!!

5. GSICS current activities for solar reflective bands at EUMETSAT
The GOS box: Absolute calibration using the SEVIRI Solar Channel system
MVIRI/VIS band
SEVIRI/ VNIR bands + HRVIS
Prepare MTG/FCI
GSICS dataset for validation purposes + GSICS product generation planned (demonstration dataset)
GSICS dataset for validation purposes + potential product (demo dataset)
No GSICS product but increased understanding of the calibration system thanks to Act.1 and Act.2
Positive feedback
The GSICS box:
Inter-calibration with MODIS using DCCs
MET-9 VIS06
MET-8 and 10 VIS06 + MVIRI
Inter-calibration with ROLO using the Moon
All SEVIRIs (currently MET-8, 9 and 10) for all VIS/NIR bands (VIS06 / VIS08 / NIR16 / HRVIS)
Feasibility study for MVIRI (Meteosat First Generation) for the VIS band
Future programs (MTG/FCI + EPS-SG/MET Image)

6. Outline GSICS activities for solar reflective bands at EUMETSAT
Current calibration system (for the solar reflective bands)
Inter-calibration with MODIS using DCCs
Main steps
Some results
Conclusions and future work

7. What about the SEVIRI solar band calibration (GOS box)?
4 solar channels ( VIS06 / VIS08 / NIR16 / HRVIS )
Specifications for the solar channel calibration?
SEVIRI = 10% accuracy + 2% of the maximum dynamic range for long-term stability
Achieved by vicarious calibration  SEVIRI Solar Channel Calibration syst. (Govaerts et al., TGRS2004)
Reference = RTM simulations of Top-Of-Atmosphere radiances (evaluated against well-calibrated polar-orbiting instruments)
Comparison with TOA measured signal above desert and ocean targets
Currently:
Meteosat 8: launch = 28/08/2002  operation = 19/01/2004
Meteosat 9: launch = 21/12/2005  operation = 18/07/2006
Meteosat 10: launch = 05/07/2012  operation = 21/01/2013
VIS06
NIR16
HRVIS
VIS08

8. Outline GSICS activities for solar reflective bands at EUMETSAT
Current calibration system (for the solar reflective bands)
Inter-calibration with MODIS using DCCs
Main steps
Some results
Conclusions and future work

9. Inter-calibration of SEVIRI with Aqua/MODIS using DCCs
Starting point:
ATBD as provided by D. Doelling et al., 2011 (
Use of MODIS Aqua as a reference
Within EUMETSAT, two-fold approach:
Implementation of an inter-calibration algorithm based on the use of DCCs for VIS06  GSICS box
Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring)  GOS box
Satellite: MET-9 (0.0 Lat / 0.0 Lon)
Band: VIS 06

10. Main steps of the method as in Doelling et al, 2011
DCC identification
Time: for MET-9 (0.0 Lat / 0.0 Lon)  11:00 < t < 14:00
Geometry:
Lat / Lon between 0.0 and +/ degrees (with respect to the SSP)
SZA and VZA < 40 degrees
DCC identification  threshold using the MODIS 11m band and SEVIRI 10.8 m (BT<205K)
Spatial homogeneity (over boxes of pixels in the “11 m” BT + in the “0.6 m” radiances)
Conversion from counts to overhead sun + spectral transformation to account for Spectral Response Function differences between MODIS and SEVIRI
Use of an Angular Distribution Model (Hu model, Hu et al. 2004)
Use of correction factors as given by the GSICS ATBD (Doelling et al, 2011)
Construction of the Probability Density Functions on a monthly basis
Derivation of the gain from the calibration equation:

11. Example of DCCs tracking with MODIS and SEVIRI as implemented
Aqua/MODIS 11m
Met-9/SEVIRI 10.8m
Missing DCCS due to test on VZA
Test on the view zenith angle
MODIS Aqua (01/04/2010 – 13:00)
SEVIRI Met-9 (01/04/2010 – 12:57)

12. Preliminary results for a few cases... as shown in September 2012
MODIS Aqua DCC radiance – 0.6 m
SEVIRI Met-9 DCC counts – 0.6 m
What is wrong???
Shift in the PDFs + double peaking for 07/2008
Shift in the PDFs
Derived gain for Julys
2008
2009
2011
2010
2012
1.2 %
1.7 %
-2.8%
-5.7 %

13. Possible reasons for bad results and solutions...
Standard uncertainty u / mean < 0.2% with
Sampling problem but not only...
MODIS PDF derived dynamically (in parallel with SEVIRI PDF)  wrong!
MODIS PDF to be derived for a time interval in early years of operations
Implementation of the ADM correction
Angle calculation
Correction calculation
Other?
Latest changes in the algorithm:
MODIS reference radiance derived from a PDF covering 07/2002 – 02/2003
MET-9 PDF built independently

14. New results... just the Julys
Significant improvement! At least apparently...

15. New results...

16. Comparisons of the PDFs before and after ADM corrections
Before ADM correction
After ADM correction
Shifted distributions!
MODIS radiances

17. Comparisons of the PDFs before and after ADM corrections
Count PDFs after ADM correction
PDFs for the original counts
MET-09/SEVIRI counts

18. Outline GSICS activities for solar reflective bands at EUMETSAT
Current calibration system (for the solar reflective bands)
Inter-calibration with MODIS using DCCs
Main steps
Some results
Conclusions and future work

19. Conclusions Implementation of the GSICS ATBD still on-going:
Requires further checks and debugging as some issues still to be solved
Uncertainty analysis still missing
Limited to the MET-09/SEVIRI VIS06 band
Future work:
Validation against D. Doelling results
Generation of a GSICS product (demo) for MET-9
Generation of validation datasets for GSICS community
Integration of the algorithm in the monitoring processing chain (MET-8, 9 and 10)
Reprocessing of the past data:
MFGs (in particular MET-7)
MSGs (MET-8 and 9)
Once problems are solved  Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring)
For the NIR16, we would be sensitive to ice crystal. So it is more difficult to do.

20. Thank you

21. Back-up slides for general purposes

22. Context... GSICS What is GSICS?
Initiative of CGMS and WMO
Effort to produce consistent, well-calibrated data from the international constellation of Earth Observing satellites
What are the basic strategies of GSICS?
Improve on-orbit calibration by developing an integrated inter-calibration system (GEO-LEO, LEO-LEO)
Best practices for prelaunch characterisation (with CEOS WGCV)
Benefits:
Improve consistency between instruments
Reduce bias in Level 1 and 2 products
Provide traceability of measurements
Retrospectively re-calibrate archive data
Better specify future instruments
EUMETSAT
CNES
JMA
NOAA
CMA
KMA
ISRO
NASA
WMO
USGS
NIST
JAXA
ROSHYDROMET
IMD
ESA

23. Context... GSICS principles
Systematic generation of inter-calibration products
For Level 1 data from passive satellite sensors (weather, climate and other environmental applications)
To compare, monitor and correct the calibration of monitored instruments to community references
By generating calibration corrections (NRT / Re-analysis applications) with specified uncertainties
Through well-documented, peer-reviewed procedures
Based on various techniques to ensure consistent and robust results
Delivery to users
Free and open access
Adopting community standards
To promote
Greater understanding of instruments’ absolute calibration
More accurate and more globally consistent retrievals
Inter-operability for more accurate environmental, climate and weather forecasting products
TRACEABILITY / UNBROKEN CHAINS OF COMPARISONS

24. Using Deep Convective Clouds as transfer target for inter-calibration of SEVIRI with Aqua/MODIS
DCCs = invariant targets
Available all around the Earth (not the case for desert for example)  seen by all GEO satellites
Well characterized and easily detectable (infra-red threshold)
Higher part of the dynamic range
Seen by well calibrated instruments on board polar satellites  calibration transfer targets
Outcome:
Improved calibration and long term monitoring of the instruments
Consistent calibration across the GEO satellite constellation
Within the GSICS framework:
ATBD as provided by D. Doelling et al., 2011 (
Use of MODIS Aqua as a reference
Within EUMETSAT, two-fold approach:
Implementation of an inter-calibration algorithm based on the use of DCCs for VIS06
Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring)