Variability of BRDF with land cover type for the west central HAPEX-Sahel super site

The issue of bidirectional reflectance distribution function (BRDF) spatial variability on the landscape and its linkages to surface characteristics has received little attention. Data sets such as those collected by the Advanced Solid-State Array Spectroradiometer (ASAS), an airborne imaging spectroradiometer with along-track pointability, are ideal for such investigations. ASAS data collected during the Hydrologic and Atmospheric Pilot Experiment (HAPEX-Sahel) near Niamey, Niger were analyzed to address spatial variability with land cover type, the effects of scale on the directional reflectance trends, and how well a simple BRDF model accounted for the principal plane reflectance trends. A hypothesis was also tested that critical elements of the BRDF of the land cover types, as captured by the terms of a simple model, could be scaled up to the BRDF of the full scene using a linear mixture model.