Bistatic scattering from rough surfaces is typically approached through the analysis of the scattered field in the conventional H and V polarization basis, which coincides with the zenith and azimuth unit vectors in a spherical reference frame. This study delves into the impacts of different choices of the transmit and receive linear basis on the performance and design of a synthetic aperture radar (SAR) mission receive-only companion. This article formalizes the rotation of the scattered wave orientation at the antenna axes of the companion with respect to the transmitted one and introduces a novel set of linear polarizations, named principal polarizations, in transmit and receive, deemed more suited to represent the scattering mechanisms of rough surfaces. Such a set is defined by the polarization bases that maximize the radar cross section. It is shown that the theoretical estimates from the proposed geometrical framework provide a good agreement with analytical and numerical simulations, performed considering state-of-the-art numerical solutions. In addition, this article promotes the hypothesis that a bistatic radar configuration, defined through the conventional H and V linear basis, presents a strong similarity, from a target information retrieval standpoint, to a monostatic compact φ-pol mode, i.e., with the transmission of a linear polarization rotated by an angle φ. The rotation φ varies over the swath and as a function of satellite separation. For baselines of 250-300 km, such as those envisioned by the European Space Agency (ESA) Harmony Earth Explorer candidate, and for steep incidence angles, an equivalent π8-pol can be achieved for rough surfaces.

Approximate numerical modeling of microwave bistatic scattering (BS) from anisotropic rough surfaces, simulating large baselines radar bistatic system, is analyzed in this contribution. The investigation is performed in the framework of the SAOCOM-CS scientific satellite mission, a small satellite under design by the European Space Agency, to be associated with the Argentinian SAOCOM 1B satellite, aiming at collecting bistatic radar data at L-band. Similar bistatic concepts are being investigated at C-band as well. The main features of the normalized radar cross section (NRCS) of the sea surface in different operating conditions are discussed. This represents the first step to assess the potentiality of bistatic radar observations of natural surfaces with large baseline, and to gather valuable information on the bistatic scattering properties for the design of future spatial missions.