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.
Highlights
In the past decades, electromagnetic (EM) scattering has attracted many researchers as well as government departments
The permittivity of the seawater calculated in Kelvin model is 48.396 − 36.603i, where i is the imaginary unit
For every facet, final contribution computed by with the diffusion contribution by for every facet, the backscattering coefficients are composed of scattering contributions of each individual facet on the final backscattering coefficients are composed of scattering contributions of each individual facet on the sea surface, either given by the Kirchhoff approximation (KA) if the region division judgement in the local vectors is satisfied or calculated by the small perturbation method (SPM)
Summary
Electromagnetic (EM) scattering has attracted many researchers as well as government departments. Among these individuals and departments, the European Space Agency alone has developed many types of radar for airborne and spaceborne platforms, including advanced. For example, launched Radarsat-1 and Radarsat-2 in 1995 and 2007, respectively These SARs provided valuable radar image data for various applications, such as environment monitoring, natural resources managing, and coastal surveillance. Those ocean image data acquired from SAR are often limited by continuous variation in ocean conditions, observation geometry and radar parameters. As a very efficient and cost-effective approach, the EM scattering estimation of marine scene becomes more valuable and has been proven
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