Investigation of polarization scatter properties using active imaging polarimetry

Abstract

This work investigates complete Mueller matrix polarization signatures in scattered light. A number of samples are studied using Mueller matrix imaging polarimetry, where samples are actively illuminated with a sequence of known polarization states. The capabilities of the Mueller matrix imaging polarimeter for scatter measurements are explored. Measuring polarization properties in scattered light from targets is important in remote sensing because polarization offers additional information unavailable from intensity measurements alone. Polarization helps discriminate surface features or material properties. The Mueller matrix contains detailed polarization and depolarization information possible for scattering objects, and every Mueller element conveys polarization coupling information. Polarization signatures are obtained at a number of different illumination and scatter angles, and a Mueller matrix bidirectional reflectance distribution function (MBRDF) in one dimension is used to compare various targets. Polarization metrics including diattenuation, retardance, and depolarization obtained from Mueller matrix data images provide methods for comparison, classification, and discrimination of targets. This work examines these reduced polarization parameters and how they vary as a function of scattering geometry, in order to determine which polarization signatures are the best discriminants for remote sensing or metrology. The Mueller matrix bidirectional reflectance distribution function, diattenuation, retardance, and depolarization properties are studied for a diverse group of manmade samples. A group of leaf samples is also studied, to see how natural samples behave and to compare natural and manmade samples. The most prevalent and useful discriminants for scattering samples appear in the depolarization data. Although this is not unexpected, these depolarization properties have not been studied in detail before and are not well described in the literature. Most depolarizing samples investigated showed an inverted Gaussian profile of depolarization magnitude versus scatter angle, with minimum depolarization for specular reflection which increases asymptotically as the scatter angle changes. Other patterns are found in the more noisy diattenuation and retardance data.