Numerical Study Of Electromagnetic Scattering For One Dimensional Freak Wave

Freak waves on the sea are potential disasters that ships can encounter. The formative mechanism is the object of increasing research. Freak waves are said to occur when the maximum wave height exceeds 2.2 times the significant wave height Hs of the background sea. Recently, analysis of synthetic aperture radar (SAR) wave mode images from the ERS and ENVISAT satellites have been applied to the detection of areas of freak wave events. In order to develop a methodology for detecting targets on the storm sea surface such as freak waves by radar, the study of electromagnetic (EM) backscattering characteristics of freak waves is meaningful.In this paper, the background, research purpose and meaning of freak wave are introduced firstly, as well as the current situation of dissertation research. Then three kinds of commonly analytical methods:Kirchhoff Approximation Method, Small Perturbation Method and the Two-scale Method are summarized by study of the electromagnetic (EM) scattering from rough surfaces. The Kirchhoff Approximation Method is used to develop the EM model of the 1D nonlinear fractal sea surfaces. We calculate the associated normalized radar cross section (NRCS) of the sea surface with this model and then compare the NRCS characteristics of the backscatter resulting from a linear fractal sea surface. The result shows that the NRCS of a nonlinear sea surface is quite different from that of a linear sea surface. An EM backscattering model is established using a Two-scale Method. Numerical results show that the NRCS of freak waves is much smaller than that of the background waves. Thus, the NRCS may be used as an indicator of freak waves.What the writer has done is as follows:analyzed and summarized three kinds of commonly and classically electromagnetic scattering analytical methods of the rough surface; developed a EM model of the 1D nonlinear fractal sea surfaces, and analyzed the characteristics of the 1D nonlinear fractal sea surfaces; developed a EM model of the 1D freak wave, and analyzed the characteristics of the 1D freak wave; at last, obtained an indicator by analyzing the result above.