- Bare soil surfaces show variation in their upward radiance depending on the direction of irradiating solar energy and the direction along which the reflected energy is viewed. Desert surfaces can exhibit both a backscattering and forward scattering characteristics. The authors tried to infer the roughness of desert rocky surfaces from their bidirectional reflectance data sets, using a geometrical reflectance model inversion technique. To achieve this, virtual equivalents of the surfaces were generated. These virtual surfaces simulate real surfaces with equal-sized opaque spheroids regularly dispersed on freely sloping plane. The capabilities of the model inversion were tested on semiarid surfaces of the Negev desert including rough rocks and smooth dune sands.