Angular Composite Facet Model with Shadowing Treatment for Backscattering from Two-Dimensional Rough Sea Surface

Abstract

Recent diverse applications on ocean wave synthetic aperture radar (SAR) images have a potential demand for individual facet scattering contribution rather than the total average radar cross-section (RCS) by statistical scattering models. However, only a few facet methods have been proposed and fewer have considered shadowing effects, which are thought to be non-negligible at large incident angle. In view of this, we proposed an angular composite facet model (ACFM) with shadowing treatment to investigate the backscattering from two-dimensional rough sea surface. First, a region division formula for ACFM without shadowing treatment is proposed to classified sea surface facets into specular facets and diffusion facets based on which kind of scattering is dominate from each facet, and the corresponding scattering contribution is calculated either by Kirchhoff approximation (KA) or by a small perturbation method (SPM) with a tilting process. Second, an electromagnetic shadowing algorithm based on facets grouping is adopted to handle the shadowing effects in a geometric manner with moderate computation complexity gained. Finally, comparisons between numerical backscattering evaluations and experimental data demonstrate that this new ACFM can attain accurate numerical results and the geometric facets grouping method is a practical way to tackle shadowing effects despite a certain acceptable gap. Therefore, the whole ACFM can simulate ocean wave SAR imaging, especially for those electrically large surfaces and to evaluate the scattering from sea surface with different local nature, such as sea spikes, foams, spilled oil, swells, and ship wake.