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

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 26.075S, 137.175E Tengger desert (China) – 17x17 km2, centered at 38.125N, 103.0E GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

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

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

CNES studies Extraction of POLDER/PARASOL and SPOT5/VGT2 images over a 2 year period (2007-2008) 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

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

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

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

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

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

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

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

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

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

Multitemporal calibration PARASOL 2008 calibration versus PARASOL 2007 VGT-2 2008 calibration versus VGT-2 2007 Good for Tengger (except blue ?) A few percent discrepancy for Simpson (temporal stability ?) GSICS GRWG Meeting – March 2011 – Patrice HENRY / CNES

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