Polarimetric bidirectional reflectance distribution function of glossy coatings

An analytic expression is derived for the angle-dependent polarimetric bidirectional reflectance distribution function (BRDF) of a glossy coating consisting of a Lambertian reflector covered by a specular dielectric layer. This model conforms to all the requirements of a real BRDF and explains the angular dependence of the polarized BRDF measurements of a glossy paint. Two common assumptions about the properties of paint coatings are shown to be incorrect: Multiple scattering by paint pigments will seldom completely depolarize the reflected energy, and, even when it does, the first surface and the volume scattering cannot be completely separated based on polarization alone. Guidelines for using the model to separate first-surface and volume scattering components are proposed.