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Received Jul 25, 2017; Accepted Nov 8, 2017
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1. Introduction
Composite electromagnetic scattering from a target above sea surface has attracted great attention in recent years, since it has a wide range of applications in target detection and tracking, remote sensing, radar imaging regime, and so forth [1–4]. In this issue, the EM scattering from the sea surface and the coupling interactions between the target and sea surface can greatly affect the overall radar target characteristics. In the present researches, many of the electromagnetic theories treat sea surface as a sort of rough surface and handle the EM simulations with various numerical methods, such as the most used method of moment (MoM) [5], finite difference time domain (FDTD) [6], finite element method (FEM) [7], and multilevel fast multipole algorithm (MLFMA) [8]. But they are generally limited by the computational requirements in terms of time and memory for handling the electrically small scale EM simulation issue, which is far from the practical needs. In comparison, high frequency approximation methods have the obvious advantage of electrically large EM simulations. Shooting and bouncing ray (SBR) method [9–12] is a popular and effective high frequency technique in consideration of the multipath coupling mechanisms, which can offer convincing physical insights and adequate accuracies. The traditional SBR method comprises a ray tracing process on the geometrical optics (GO) and physical optics (PO)/Kirchhoff approximation (KA) method to handle the coupling interactions among the meshed facets of the simulation model. In this process, a fine mesh size (smaller than 1/10 of the incident wavelength) for both the target and the sea surface is required. However, it can cause a heavy computation burden, which bottlenecks SBR by not being able to maintain both the accuracy and the efficiency in calculating the composite scattering from a target at the practical maritime scene with an electrically very...