Recent progress on forward scattering modeling for GNSS reflectometry

A geometric optics limit of the Kirchhoff approximation is widely used for modeling the bistatic radar cross section of the ocean surface. The question of practically acceptable accuracy of this approximation for GNSS-R applications remains open. In this paper we use more accurate approximation, the small slope approximation to assess the validity of the geometric optics model. Here, we present the results of calculations of the bistatic radar cross section for L-band circular polarization signals using both the geometric optics model and the small slope approximation. Another issue addressed in this paper is the sensitivity of the modeled bistatic radar cross section to wind direction. Two semi-empirical surface spectral models are employed and in- and out-of-plane geometries are considered. Also, using the small slope approximation we investigate the sensitivity of the azimuthal angle dependence of the bistatic radar cross section to wave fetch.