The retrieval of land surface albedo in rugged terrain

Land surface albedo may be derived from the satellite data through the estimation of a bidirectional reflectance distribution function (BRDF) model and angular integration. However many BRDF models do not consider explicitly the topography. In rugged terrain, the topography influences the observed surface reflectance, and varies the distribution of downward irradiance, so that BRDF and angular integration will change from flat area to rugged area. This paper details an approach to take into account the topography influences on the surface reflectance, and outlines an algorithm considering the topographic factor. This algorithm makes use of a Digital Elevation Model (DEM) to correct the incidence angle and the reflection angle in a BRDF model, and performs the angular integration based on the different distribution of downward irradiance between a flat area and a rugged area. This approach was applied to HJ-1A/B data and the results were compared with the ones obtained with the algorithm designed for NASA's MODIS data.