| The study of electromagnetic (EM) scattering from sea surface environment has great application value on the areas of ocean remote sensing, ocean environment detection and recognition of maritime targets. However, scattering signatures from radar will often give rise to supre scattering phenomena of sea spikes, high polarization ratios and large Doppler offsets, and how to describe and explain these phenomena is a hot topic and key point. In face, the nonlinearity of ocean wave and breaking wave are the main contributor to these supre scattering phenomena. And there are some difficulties for the study of EM scattering from nonlinearity of ocean wave and breaking wave, and the mainly difficulty displays in the following points:First, the complex motion of ocean waves and the random influence of the wind or atmosphere above the sea surface will make the ocean waves change very random and nonlinear; Second, the ocean waves will become steep and even breaking with the increase of wind speed. Turbulence, foams, and droplets will arise with the occurrence of wave breaking, which seems impossible to be described by the existing mathematical theory; Third, the traditional EM scattering theory can not deal with the scattering problem of complex structure of breaking wave and indicate super scattering phenomena very well. Therefore, this dissertation is aimed at the study of the EM scattering from the nonlinearity of ocean wave and wave breaking. The main works are as follows:1. Based on the narrow-band Lagrange model, a nonlinear fractal sea surface is establish, which is with vertical and horizontal skewnesses. The EM scattering characteristics of the nonlinear model is calculated by applying the method of second-order small-slope approximation. The calculation result can indicate the value of the nonlinearity on the radar cross section and Doppler spectrum. And also, the influences of the vertical and horizontal skewnesses on the scattering result are discussed.2. A semiempirical breaking points distribution is obtained based on the slope criterion and the measured breaking wave coverage model. On the basis of the breaking points distribution model, the mesoscale breaking wave model is introduced to approximate the breaking wave on the sea surface. The contribution of breaking wave is considered by letting the breaking wave model with different parameters randomly distributed at the breaking points. Accounting for the contribution of breaking waves, the backscattering coefficients and Doppler spectrum are analyzed.3. The modified backscattering coefficients of sea surface with breaking wave can be obtained by accounting for the breaking wave coverage model and the statistical averaging the scattering coefficients from mesoscale breaking waves with different parameters. Based on this, the distribution of scattering coefficient of sea surface are applied for SAR imaging, and the SAR imaging model of sea surface including the contribution of breaking is obtained.4. Different scales of breaking waves have been obtained by employed the commercial computational fluid dynamics software FLUENT. The generated breaking waves are connected with the EM scattering, and the scattering characteristics of the breaking waves are analyzed by the method of moments. The results can indicate the super scattering characteristics of sea spikes and high polarization ratios.5. The turbulence structures after breaking are simulated by FLUENT, and the turbulence structures of different stages are obtained. And also, the scattering characteristics of the turbulence structures are calculated with the method of moments. Besides, the turbulence structures generated by a propeller are simulated and different intensity of turbulence structures are generated with different rotating speeds. The scattering characteristics of turbulence structures have also been analyzed.This dissertation has made corresponding study of the nonlinearity of sea surface, the approximation model of breaking and numerical model of breaking. The semiempirical breaking wave model can act as a basis for establishing the EM scattering model of complex sea surface environment, and the scattering results of the simulated breaking waves and turbulences can provide more bases to explain the anomalies of EM scattering from sea surfaces.
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