Ocean-scattered polarized bistatic radar signals modeled with small-slope approximation

Currently, theoretical predictions for the performance of remote-sensing applications using Global Navigation Satellite System (GNSS) reflected signals such as altimetry and scatterometry are based mostly on the geometric optics (GO) limit of the Kirchhoff (physical optics) model. For a bistatic forward-scattering regime and for a predominant, left-hand circularly polarized (LHCP) scattered component, the GO model works quite satisfactorily. However, the GO gives incorrect predictions for a right-hand circularly polarized (RHCP) scattered component. Also, it is not applicable for a scattering process at wider angles, which are affected by diffraction or Bragg scattering. The use of the first-order SSA for calculating the LHCP scattered component of the GNSS signal was demonstrated previously [1]; however, it cannot correctly predict the RHCP scattered component and the effects of out-of-plane bistatic scattering. The second-order SSA is needed to overcome these difficulties. Here, we present results of calculations for bistatic LHCP and RHCP radar cross sections for the case of ocean surface elevations described by Gaussian statistics and the empirical wave spectrum.