The study focused on scaling the surface bidirectional reflectance of the rugged surfaces from fine to coarse spatial resolutions. Different bidirectional shadowing functions were compared with computer simulation techniques such as raytracing and radiosity based on the simulated surfaces and real 30 m Digital Elevation Model （DEM） data. All algorithms show that topography has significant effects on radiation scaling. However

comparisons also reveal large differences among models suggesting that further development is needed for accurate estimation of topographic effects on BRDFs.