Developing a generalized BRDF model from experimental data

In this paper, we present a model for BRDF that can be developed from a limited set of experimentally observed data, and which then can be used for predictive purposes in scene-generation or sensor-performance applications. The model is physics based and can be as detailed as desired, depending on the scope of experimental data available. Basic input parameters required are the complex refractive index of the material, or the directional hemispherical reflectivity (DHR) for s- and p-polarized radiation. At least one BRDF measurement is needed to determine the angular spread function. Incorporating BRDF measurements at several angles of incidence into the model yields better accuracy for describing behavior such as forward scatter, depolarization, the participation of volumetric and surface-scattering mechanisms in layered surfaces, diffuse-scatter coherence properties, and narrowing of the angular spread function which provides an indication of optical depth. Illustrations and demonstrations of the methodology are drawn from data sets measured on bead-blasted aluminum, automotive paint incorporating a clear-coat layer, and green low-gloss vehicle paint.