1. Study of Asian and Australian desert sites for sensor cross-calibration in the VPIR range
Patrice Henry, Bertrand Fougnie, Sophie Lacherade, Philippe Gamet, Denis Blumstein - CNES Thomas Colin - CS
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

2. Sites selection Study performed in 2009 by B.J. Sohn using MODIS data
Analysis of different properties
Simultaneous view from MTSAT, COMS, FY2C
Target brightness
Temporal stability
Spatial stability
NDVI
Data yielding ratio
Solar zenith angle, satellite viewing angle
2 sites proposed to GSICS mid 2009
Simpson desert (Australia) – 50x50 km2, centered at S, E
Tengger desert (China) – 17x17 km2, centered at N, 103.0E
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

3. Simpson desert 0.5 deg Lakes
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

4. Tengger desert
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

5. CNES studies
Extraction of POLDER/PARASOL and SPOT5/VGT2 images over a 2 year period ( )
Data processing (cloud screening…) and insertion in the SADE data base
Sites analysis using ‘standard’ CNES tools
Spatial, spectral, temporal and directional behaviour
PARASOL and VGT2 cross calibration
Results comparison with 3 African desert sites : Algeria 3, Libya 1 and Libya 3
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

6. General view of the 5 sites
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

7. Snow filtering over Tengger site
Large reflectance scaterring in winter 07/08
Tengger site
Need for snow filtering
23 Nov. 2007
1 Feb. 2008
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

8. Brightness behaviour Simpson lightly less bright than African sites
Mean TOA PARASOL reflectance
Mean TOA VGT2 reflectance
Simpson lightly less bright than African sites
Tengger highly less bright than African sites
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

9. Spectral behaviour Simpson very similar to African sites
Mean TOA PARASOL reflectance normalized by the blue reflectance
Simpson very similar to African sites
Tengger more ‘blue’ than the other sites
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

10. Spatial behaviour
Simpson
Tengger
Algeria 3
Libya 1
Libya 3
PARASOL TOA reflectance standard deviation
Simpson lightly less homogeneous than African sites (x2)
Tengger highly less homogeneous than African sites (x3)
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

11. Same level of seasonal variation
Temporal behaviour (1)
Simpson
Tengger
Algeria 3
Libya 1
Libya 3
PARASOL TOA reflectance versus date
Same level of seasonal variation
but …
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

12. Temporal behaviour (2)
Simpson
Tengger
Algeria 3
Libya 1
Libya 3
PARASOL TOA reflectance normalized by the red reflectance
Spectral dependance of seasonal effect on spectral range for Tengger (vegetation ?)
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

13. Directional behaviour
Simpson
Tengger
Algeria 3
Libya 1
Libya 3
VGT2 TOA reflectance versus zenith viewing angle
Very similar directional behaviour
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

14. VGT2 calibration versus Parasol
Mean VGT2/PARASOL calibration results
Standard deviation of VGT2/PARASOL calibration results
Good consistency for the red
Simpson : 3% higher in the blue, 3% lower in the NIR
Tengger : 6% higher in the blue (very high s…)
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

15. Multitemporal calibration
PARASOL 2008 calibration versus PARASOL 2007
VGT calibration versus VGT
Good for Tengger (except blue ?)
A few percent discrepancy for Simpson (temporal stability ?)
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

16. Conclusion
For the 2 sites : less suitable characteristics for calibration than African sites
Tengger
Very small site
Not so homogeneous
Calibration standard deviation much higher than other sites
No winter calibration opportunity (potential snow coverage)
No good results for sensors cross calibration
Simpson
Lightly less homogeneous than Afircan sites
Poor temporal stability : bad results for multidate calibration
CNES does not intend to extend SADE data base with other PARASOL and VGT2 data but MERIS data will be added
GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES