POSTEL Radiation BRDF
The “radiation” biogeophysical products of Postel are spatialized variables derived from optical or micro-wave sensors measurements acquired over many years at regional to global scales. The Bidirectional Reflectance Distribution Function (FDRB) describes how terrestrial surfaces reflect the sun radiation. Its potential has been demonstrated for several applications in land surface studies (see Bicheron and Leroy, 2000). The space-borne POLDER-1/ADEOS-1 instrument (November 1996 – June 1997) has provided the first opportunity to sample the BRDF of every point on Earth for viewing angles up to 60°-70°, and for the full azimuth range, at a spatial resolution of about 6km, when the atmospheric conditions are favorable (Hautecoeur et Leroy, 1998). From April to October 2003, the land surface BRDF was sampled by the POLDER-2/ADEOS-2 sensor. From March 2005, the POLDER-3 sensor onboard the PARASOL microsatellite measures the bi-driectional reflectance of the continental ecosystems. These successive observations allowed building : 1- a BRDF database from the 8 months of POLDER-1 mesurements : The POLDER-1 BRDF data base compiles 24,857 BRDFs acquired by ADEOS-1/POLDER-1 during 8 months, from November, 1996 to June, 1997, on a maximum number of sites describing the natural variability of continental ecosystems, at several seasons whenever possible. The POLDER-1 bidirectional reflectances have been corrected from atmospheric effects using the advanced Level 2 algorithms developed for the processing line of the ADEOS-2/POLDER-2 data. The BRDF database has been implemented on the basis of the 22 vegetation classes of the GLC2000. 2- a BRDF database from the 7 months of POLDER-2 measurements : The POLDER-2 BRDF data base compiles 24,090 BRDFs acquired by ADEOS-2/POLDER-2 from April ro October 2003, on a maximum number of sites describing the natural variability of continental ecosystems, at several seasons whenever possible. The POLDER-2 bidirectional reflectances have been corrected from atmospheric effects using the advanced Level 2 algorithms described on the CNES scientific Web site. The BRDF database has been implemented on the basis of the 22 vegetation classes of the GLC2000 land cover map. 3- 4 BRDF databases from one year of POLDER-3 measurements :The LSCE, one of the POSTEL Expertise Centre, defined a new method to select the BRDFs from POLDER-3/PARASOL data acquired from November 2005 to October 2006 in order to build 4 BRDF databases. 2 MONTHLY databases gathering the best quality BRDFs for each month, independently : one based upon the IGBP land cover map, the second based upon the GLC2000 land cover map. 2 YEARLY databases designed to monitor the annual cycle of surface reflectance and its directional signature. The selection of high quality pixels is based on the full year. The first database is based upon the IGBP land cover map, the second one is based upon the GLC2000 land cover map.
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