The role of specular reflectance in surface anisotropy

For smooth surfaces, specular reflection constitutes a major source of anisotropy in the surface bidirectional reflectance and introduces a strong illumination angle dependence in diurnal albedo. A prior formulation has been employed by the authors to account for the surface anisotropy of other natural surfaces. It is shown that this formulation is appropriate to successfully explain the specular characteristics of other rough surfaces as well as that of the ocean. The angular dependence of the diffuse component of the reflected radiance is explained using the Ahmad-Deering formulation, which is based on Chandrasekhar's radiative transfer solution. Results for a smooth silt-playa lake bed in a volcanic region of Nevada are presented. It is shown that this formulation is capable of explaining the specular features measured in the field and can be effectively used in any surface bidirectional reflectance model.