1. Crossing Multiple Methods
GSICS Annual Meeting 24-28th March 2014, Darmstadt, Germany
Synergic Calibration
Crossing Multiple Methods
Bertrand Fougnie
and CNES Calibration Center
(CNES-DCT/MO and CNES-DCT/ME)

2. Crossing Multiple Methods
Synergic Calibration
Crossing Multiple Methods
Context
CNES Calibration Tool Box
Outlines
advantage / drawbacks or limitations
Application for PARASOL end-of-life reCalibration
Application in the OCR-Virtual Constellation context
Application to SEVIRI

3. Context
In the past years, several calibration methods were developed using natural targets
various calibration methods, different approaches
operational configuration now available
In the past years, several sensors provided extensive calibration time series
a large experience has been developed on the use of each method
a feedback exists on the real advantage and limitations

4. CNES Calibration Tool Box (MUSCLE)

5. SADE/Muscle – The Operational Arsenal
Several calibration methods are operational
Desert, Rayleigh, Sunglint, Cloud-DCC, Antarctica, Moon
Deserts
Domes
Sunglint
Moon
DCC
Rayleigh

6. SADE/Muscle – The Operational Arsenal
Muscle / SADE
(Tools) (Database)

7. Outlines, strength, limitations
Several calibration methods are available
Desert, Rayleigh, Sunglint, Cloud-DCC, Antarctica, Moon
Each target has its own behavior :
Magnitude: from very dark to very bright
Spectral shape : from white to very pronounced
Angular signature : from nearly uniform to large BRDF
Polarized properties : from non-polarized to nearly fully polarized
Short-term stability : from variable to fully stable
Long-term stability : from seasonal variable to fully stable
So efficiency range …
Indicative behavior of targets
May sensitively vary with various parameters

8. Synergic : What does it mean ?
So the observation is :
Calibration methods are like “Bordeaux Wines” : every method is good
but in fact, all the methods show limitations
it is impossible to address all calibration/radiometric aspects (the so-called “system calibration”) with one single method
Basic idea = develop the synergic use of several method in order to :
take advantage of the complementarities of all method
document the confidence from consistency between methods
improve the “system calibration” when integrating various results
assess radiometric aspects others that the absolute calibration
“Indicative” cartography – range of efficiency for each method

9. Absolute cal. Rayleigh Scattering Interband cal. Desert sites
The “Great Mixture” !
Absolute cal.
Rayleigh Scattering
Interband cal.
Desert sites
Field-of-view cal.
Snow (domes)
Temporal monitoring
Clouds (DCC)
Cross-calibration
Sunglint
Polarisation
Moon
Characterization
Method

10. Applications to - PARASOL end-of-life reCalibration - Validation of MERIS calibration - MODIS-Aqua validation - SEVIRI evaluation

11. 1/ PARASOL end-of-life reCalibration
Recent example#1 = PARASOL :
bidirectional polarimeter :
± 50° wide fov optic + 2D focal plane 1400x2000km²
up to 16 viewing directions
9 channels, and 3 polarized (490, 670, and 865nm)
a “3M” concept
Multi-directional + Multi-spectral + Multi-polarization
No on-board calibration device
in-flight calibration only based on natural targets
(Fougnie et al., IEEE-TGARS, )
Multi-method Synergic Approach
Launched in dec-2004, on A-train up to end-2009
currently drifting, End-of-life in September 2013
3MI follow-on serie of instrument is expected on Post-EPS (~2018)
2000 km
along-track
1400 km
cross-track
Satellite
PARASOL
image
zenith viewing angle
⇒ No on-board
calibration
device

12. 1/ PARASOL end-of-life reCalibration
Synergic calibration for the in field-of-view evolution
Clouds suppose the reference band is stable (765nm)
Desert (reference = POLDER1) : more noisy, validation of cloud results
Combination of 765 from desert (small evolution) + interband from clouds
Desert
865/ / / /
Clouds
combination

13. 1/ PARASOL end-of-life reCalibration
Synergy : calibration of the temporal monitoring
Calibration versus month
B565 = 0.11
B865 = 0.024
B1020 = 0.018
B765 = 0.01

14. 1/ PARASOL end-of-life reCalibration
Synergic calibration for the calibration adjustment
Final adjustment = best compromise
Confidence where consistency is observed : e.g. 865nm
Investigation conducted when curious behavior are observed :
443nm due to a stray light problem
565nm over clouds due to ozone
Remaining investigations to improve the results : e.g. versus MERIS

15. 2/ Validation of MERIS calibration
Validation of the monitoring
Interband stability over DCC and desert : perfect stability, artifacts
reference
VIS
DESERT
DCC
reference
reference
NIR

16. 2/ Validation of MERIS calibration
Validation of the interband behavior
Interband over DCC and sunglint
GLI (10 yrs) N=30,560
442 nm
DCC (10 yrs) N=9,391
442 nm
vs reflectance
vs reflectance
GLI (10 yrs) N=30,560
665 nm
DCC (10 yrs) N=9,391
665 nm
vs reflectance
vs reflectance
GLI (10 yrs) N=30,560
885 nm
DCC (10 yrs) N=9,391
885 nm
vs reflectance
vs reflectance

17. 2/ Validation of MERIS calibration
Behavior within the field-of-view : Versus viewing angle
DES (10 yrs) N=15,963
DES (10 yrs) N=15,963
442 nm
620 nm
vs VZA
vs VZA
RAY (10 yrs) N=99,631
RAY (10 yrs) N=99,631
620 nm
442 nm
vs # camera
vs # camera
DCC (10 yrs) N=9,371
DCC (10 yrs) N=9,371
620 nm
442 nm
vs # camera
vs # camera

18. 2/ Validation of MERIS calibration
Validation of the calibration through Synergy
Agreement – validation within 1%
Some light discrepancies :
1/ known limitation of the method
2/ unknown limitation of the method
3/ significant signature ? May be under the accuracy of individual method, but Synergy may help !
Compare to System Ocean Color Vicarious Calibration

19. 3/ Aqua-MODIS validation
Validation of the radiometric stability
Absolute and Interband over Desert and Rayleigh
Calibration stability
Rayleigh
Desert
Interband stability
Desert
Rayleigh

20. 3/ Aqua-MODIS validation
Validation of the interband behavior for SWIR
Interband over Sunglint and Desert
GLI (Dec N=7,861)
DES ( N=4,839)

21. 3/ Aqua-MODIS validation
Validation of the calibration through Synergy
Agreement – validation within 1% for OC bands, some discrepancies for Land bands
Some light discrepancies :
1/ known limitation of the method
2/ unknown limitation of the method
3/ significant signature ? May be under the accuracy of individual method, but Synergy may help !
Compare to System Ocean Color Vicarious Calibration
Lunar Calibration

22. 4/ Application to GEO and SEVIRI
Same approach for GEO sensor with SEVIRI/MSG2
Rayleigh, Desert, Sunglint
This preliminary result has to be developed
Backscattering signature on Rayleigh scattering to be explained
Angular dependency with sun azimuth angle on Desert to be investigated
Cross-calibration with MODIS to be generated (here very preliminary results)

23. Final comments Cross different methods =
a powerful diagnostic whatever the nominal calibration method
a coverage of most of the system calibration aspects (absolute, angular, spectral, temporal, cross)
A good consistency between multiple methods =
a good confidence on the final calibration (nominal + validation)
a “realistic” estimation of the final calibration accuracy (as if the theoretical evaluation of the error budget for the nominal cal method is excellent)
no radiometric artifacts remain : such as non-linearity, straylight, offset, polarization, inside the field-of-view…
Differences between results from methods =
need investigation to understand why – radiometric artifact
require a good knowledge of the instrumental characteristics
The state of the art cannot be reached through only 1 method
One calibration method has its own accuracy : e.g. 2%, 3%...
we can try to go down this limitation by mixing results
A good consistency between sensors AND for multiple methods =
a very high level of confidence can be claimed