Active detection of off-diagonal Mueller elements of rough targets

Off-diagonal Mueller elements indicate polarization transformations as occur in polarizers and retarders. Target scattering may also generate off-diagonal elements, which then provide information unavailable from passive polarimetry or active depolarization measurements. The target and observation parameters required in active, monostatic systems for the detection of off-diagonal Mueller elements due to target scattering are investigated. The dependences of off-diagonal elements on incident angle, surface roughness, material composition, and target symmetry are investigated through analysis and measurements from two polarimeters. Multiple scattering and anisotropic roughness, which may result either from innate surface anisotropy or oblique incidence, are found to generate off-diagonal elements in the monostatic geometry. Results from a polarized microfacet scattering model corroborated with polarimeter data reveal a particular application of off-diagonal Mueller elements in the discrimination of dielectric from metal targets, of similar roughness.