CNES Activities in the Framework of GSICS Patrice Henry, Denis Blumstein, Denis Jouglet - CNES Thomas Colin - CS GSICS Executive Committee – WMO.
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CNES Activities in the Framework of GSICS Patrice Henry, Denis Blumstein, Denis Jouglet - CNES Thomas Colin - CS GSICS Executive Committee – WMO Geneva – June 06-08 2011 AIRS/IASI Intercalibration — sample of results ■ Intercalibration AIRS/IASI SNO events (high latitude only) operational in the IASI TEC activated on a regular basis 3 months ■ Updated to handle IASI L1C Day-2 products (from May 2010) GSICS Executive Committee – WMO Geneva – June 06-08 2011 2 IASI-A / IASI-B Intercalibration — Cal/Val preparation IASI-A IASI-B 16km 10km ~39° common zone ■ Metop-A / B are on the same trajectory (180 deg apart) Overlap between the swath of the 2 IASI instruments ■ Observation by 2 IASI of a same region on ground possible 50 min between overflight of a same point At all latitudes ■ Use of common zone where Sat Viewing Angle are “equal” common view by IASI-A / IASI-B We limit ourself to 4 IASI pixels width Satellite Viewing Angle between 0 deg (high latitude) and 39 deg (equator) ■ Limitation to uniform and stable (in time) geophysical situation GSICS Executive Committee – WMO Geneva – June 06-08 2011 3 Study of Asian and Australian Desert Sites for Sensor cross-Calibration in the VPIR Range ■ Sites selected in 2009 by B.J. Sohn using MODIS data Simpson desert (Australia) – 50x50 km2, centered at 26.075S, 137.175E Tengger desert (China) – 17x17 km2, centered at 38.125N, 103.0E ■ CNES studies Extraction of POLDER/PARASOL and SPOT5/VGT2 images over a 2 year period (2007-08) 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 ■ For the 2 sites : less suitable characteristics for calibration than African sites Tengger Very small site and not so homogeneous Calibration standard deviation much higher than for other sites No winter calibration opportunity (potential snow coverage) and poor results for sensors cross calibration Simpson Lightly less homogeneous than African sites Poor temporal stability : bad results for multidate calibration ■ No SADE extension with other PARASOL and VGT2 data but MERIS data will be added GSICS Executive Committee – WMO Geneva – June 06-08 2011 4 General view of the 5 sites Simpson Algeria 3 GSICS Executive Committee – WMO Geneva – June 06-08 2011 Tengger Libya 1 Libya 3 5 Sites temporal behaviour 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 Executive Committee – WMO Geneva – June 06-08 2011 6 VGT2 calibration versus Parasol Mean VGT2/PARASOL calibration results Standard deviation of VGT2/PARASOL calibration results • Good consistency for the red range • Simpson : 3% higher in the blue, 3% lower in the NIR •Tengger : 6% higher in the blue (very high s…) GSICS Executive Committee – WMO Geneva – June 06-08 2011 7 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 Executive Committee – WMO Geneva – June 06-08 2011 8 Deserts cross Calibration Method Assessment ■ Study performed to provide inputs for deserts calibration error budget ■ TOA reflectance of different sensors (MODIS, MERIS, PARASOL, VGT, ETM+) simulated using Hyperion hyperspectral TOA data Aqua/MODIS vs MERIS MERIS vs Aqua/MODIS ETM+ vs Terra/MODIS VGT2 vs Parasol/POLDER Parasol/POLDER vs Aqua/MODIS Parasol/POLDER vs MERIS ■ Different cross calibration method tested : Same geometry (data pairs simulated with the same Hyperion data) Close geometry (data pairs from close geometry Hyperion pairs) Closest spectral band (direct band to band comparison to spline interpolation) Omitted spectral bands to assess interpolation and extrapolation effect GSICS Executive Committee – WMO Geneva – June 06-08 2011 9 Acquisition geometry error ■ Comparison of same geometry and close geometry calibration Example of Aqua/MODIS vs MERIS Same geometry Close geometry ■ Very important increase of standard deviation (x2 to x10) but small effect on the mean value (0.5% max.) But viewing geometry is always the same (Hyperion geometry). Discrepancies are only due to : sun angles, atmospheric correction, annual variation of the site GSICS Executive Committee – WMO Geneva – June 06-08 2011 10 Reflectance interpolation error ■ Comparison of spline interpolation and band to band calibration Example of Landsat/ETM+ vs Terra/MODIS Spline interpolation Band to band ■ Increase of cross calibration unaccuracy ■ Increase of site to site discrepancy Band to band calibration shall be limited to very similar bands (VGT2/VGT1, Aqua/MODIS vs Terra/MODIS…) GSICS Executive Committee – WMO Geneva – June 06-08 2011 11 Reflectance extrapolation error ■ Comparison of cross calibration with different set of reference band Example of Aqua/MODIS vs MERIS Without 412 nm as reference band With 412 nm as reference band ■ Very important error due to extrapolation (> 20%) Site reflectance profiles do not allow any extrapolation neither in the blue or in the SWIR… GSICS Executive Committee – WMO Geneva – June 06-08 2011 12 Main Conclusions of the Study ■ Interpolation (extrapolation !) error : main contributor of the error budget Adequate choice for the reference sensor Good knowledge of the site reflectance Good knowledge of the directional effects over the sites ■ Statistics can take afford for atmospheric correction errors Necessity for a great amount of data Risk a small bias due to uncertainty on aerosol content ■ Good accuracy for multitemporal calibration ■ Sensors cross calibration only possible for ‘close’ spectral bands a more complete error budget has been undertaken GSICS Executive Committee – WMO Geneva – June 06-08 2011 13 SADE opening to GSICS and CEOS ■ Few feedbacks from beta-users : only one (very positive…) ■ SADE access through CNES scientific mission website http://smsc.cnes.fr/CALIBRATION/ Password mandatory ■ No procedure yet available for password delivery (contact Denis Blumstein or Patrice Henry) ■ A complete reprocessing of SADE exported files is foreseen for Nov. 2011 Data extension up to mid 2011 New sensors : Terra/Modis Landsat 7 Theos New MERIS reprocessing VGT1 updated calibration GSICS Executive Committee – WMO Geneva – June 06-08 2011 14