Bidirectional reflectance distribution function signatures of major biomesobserved from space

Land surface bidirectional reflectance distribution function (BRDF) measure ments were acquired from November 1996 to June 1997 at global scale and 6 k m spatial resolution with the POLDER instrument onboard the ADEOS-1 satelli te. We selected 395 BRDF data sets on areas distributed on the 17 biomes of the IGBP 1-km land cover classification (DISCover data set) at 443, 670, a nd 865 nm, at several periods (November and December 1996, May and June 199 7). The selected BRDF data are characterized by a low noise level, a suffic ient number of clear days during the month, and a roughly even sampling of directional space. The data show large differences of the directional and s pectral signatures of the various land cover classes, both in shape and in magnitude. Except for the desert and ice classes, all signatures present a peak in the backscattering direction, with sometimes an additional strong p eak in the specular direction for wetlands. The data permit an assessment o f the BRDF temporal evolution due to changes of surface state or Sun elevat ion, as well as a quantification of the BRDF variability within a land cove r class. The maximum error level of the BRDF database is estimated to be of the order of 0.01 and 0.03 (in units of reflectance) in the red and near i nfrared, respectively. The BRDF database is available to the science commun ity through the Internet. It should be helpful for the prototyping of vario us science applications, including the test of radiative transfer models an d algorithmic schemes of corrections of angular effects on remote sensing d ata. As an example of application of the database, various semiempirical BR DF models published in the literature are tested and intercompared. Whereas all tested models catch reasonably well the overall shape of the BRDF, som e differences appear between the red and the near infrared, between classes , and between models, which the use of the database permits to quantify.