Reflection Functions for Inhomogeneous Land Surfaces

Bidirectional reflection distribution functions (BRDFs) of inhomogeneous land surfaces that consist of protruding structures on a flat suface are modeled. The components are allowed to have individual reflection properties. Modeling the BRDFs takes into account the simultaneous influence of vertical structure and of different anisotropic BRDFs assigned to the components. A realistic simulation of bare soil and partly or fully vegetated surfaces with a pronounced 3-D structure is possible. A sensitivity study shows to what extent surface reflection is affected by vertical structure and zenith angle of incidence when different BRDFs are assigned to both surface components. The results can be used to decide for which conditions area weighted adding of BRDFs from homogeneous surfaces is sufficient to get an average BRDF for an inhomogeneous surface. It tends to be insufficient when vertical structure, zenith angle of incidence, and the albedo of the ground increase in relation to the albedo of the protrusions.