Link Budget Analysis for the Modeling of GNSS-R Sea Surface Returns in Far-from-Specular Acquisition Geometries

For the analysis of sea surface using Global Navigation Satellite System-Reflectometry (GNSS-R), Geometrical Optics (GO) is typically adopted for modeling scattering around the specular reflection direction, where conventional GNSS-R receivers operate. However, the exploitation of GNSS-R for maritime surveillance applications, e.g., ship detection, is feasible in far-from-specular acquisition geometries, where the validity of GO is questionable. In this paper, we present the results of a link budget analysis for the sea surface return in arbitrary viewing geometries. The study is aimed at comparing GO with a more accurate closed-form bistatic two-scale model, named BA-PTSM, for the simulation of GNSS-R signals in acquisition geometries other than the conventional forward-scattering one. Numerical results show that a reliable simulation of airborne GNSS-R signals in far-from-specular acquisition geometries requires sea surface scattering models more accurate than GO, e.g., BA-PTSM.