Spatial distribution of Sahelian land surface properties from airborne POLDER multiangular observations

This paper presents the spatial distribution of land surface parameters in southwestern Niger, a region composed mainly of shrub and grassland fallows , millet crop, and tiger bush. The regional patterns of the surface albedo, the leaf area index, the fractional vegetation cover, and the fraction of absorbed photosynthetically active radiation are estimated through the grow ing season from airborne POLDER (Polarization and Directionality of Earth R eflectances) data acquired during the Hydrologic Atmospheric Pilot Experime nt in Sahel (HAPEX-Sahel). The retrieval of these parameters is via a bidir ectional reflectance model, appropriate vegetation indices, and Sun-view ge ometries. Comparison of the POLDER-derived surface parameters with airborne and ground measurements shows that the procedure generally performs well, enhancing the ability to constrain soil-vegetation-atmosphere transfer (SVA T) models in the Sahel area by providing spatially averaged and updated inf ormation. This will enable a more valid assessment of the role of the land surface in determining the Sahelian climate, with a better determination of the scaling effect of surface processes. Although the algorithms described in this work rely primarily on multiangular observations, such as those pr ovided by spaceborne POLDER data sets, they should be useful in a number of remote sensing applications.