Unified scatter model for rough surfaces at large incident and scatter angles

A new unified surface scatter model has been developed that produces accurate results for rougher surfaces than the classical Rayleigh-Rice vector perturbation theory and for larger incident and scattered angles than the classical. Beckmann-Kirchhoff theory. It is a generalization of the linear systems formulation developed by Harvey and Shack in the mid 1970s. The scattered light behavior is characterized by a two-parameter family of surface transfer functions. The rather computationally intensive process of calculating the scattered intensity from rough surfaces at large incident angles is described and shown to agree well with experimental data. Furthermore, the smooth-surface approximation to this new generalized surface scatter theory yields an improved solution to the inverse scattering problem of characterizing optical surfaces from BRDF measurements. The new obliquity factor greatly reduces the ubiquitous and annoying "hook" at the high spatial frequency end of surface PSDs predicted by the Rayleigh-Rice theory. Comparisons of this new theory and the Rayleigh-Rice theory will be made with experimental BRDF measurements provided by John Stover, author of the companion paper entitled "Limitations of Rayleigh-Rice perturbation theory for describing surface scatter".