RADARSAT Constellation Mission’s Operational Polarimetric Modes: A User-Driven Radar Architecture

Abstract

Canada’s Earth-observing RADARSAT Constellation Mission (RCM) is intended to serve operational users. The users’ main objectives were to have routinely available high-quality quantitative information about their applications, with large area coverage potential. That two-part requirement was sufficient to establish an innovative synthetic aperture radar (SAR) polarimeter’s end-to-end system profile, the hybrid compact polarimetric (HCP) architecture. HCP’s essential and defining characteristic is circularly polarized transmission. This is sufficient to evaluate the backscatterer Stokes vector, but only half of the scattering matrix elements are measured. Hence image classification methodologies for linearly polarized full- (or quad-) pol (FP) radars that depend on knowledge of all four of the scattering matrix elements if applied to HCP-derived data lead to erroneous results. HCP-appropriate classifications are based on the Stokes vector. Related methods traditionally used for radar astronomy—for which circularly polarized transmission is the norm—are reviewed. Those known methods are extended, bringing to light fundamental characteristics of a polarimetric electromagnetic field. Analysis tools appropriate for HCP’s polarimetric data are introduced. The resulting polarimetric portraits—defined as the Stokes vector of the backscattered field in response to balanced illumination of the scene—from FP and HCP polarimeters are shown to be equivalent.