| Overturning wave cast is considered to be a reason of sea-spike generation,which increases the risk of radar false alarms.Therefore,study on electromagnetic scatteing characteristics of the 2-D dynamic sea surface with overturning wave is of great significance.In this paper,the main works focus on the discuss of the modelling of the overturning wave,the backscattering and the Doppler spectrum.Firstly,the improved time-varying rough overturning wave crest is modeled,and the two-dimensional(2-D)sea surface model is established,which combined the improved time-varying rough overturning wave with the traditional PM sea surface.Based on this,the backscattering of overturning wave model and the Doppler spectrum of above-mentioned 2-D sea surface model is calculated and studied by Mo M.At the last,the effect of overturning waves on the sea spikes is analysed systematically.The main works of the paper are as follows:1.The basic theory of Mo M is introduced,and the integral equations and the matrix equations for calculating the electromagnetic scattering of 2-D dielectric rough surface are discussed in detail,and the calculation formula of backscatteing coefficient is provided.The electromagnetic scattering characteristics of 2-D Gaussian dielectric rough surface is also analysed.2.At for the modeling of overturning wave is concerned,a time-varying overturning wave crest model is modeled considering the effect of wind speed on the width and height of overturning wave.Based on this,the improved time-varying rough overturning wave crest model is proposed,and the roughness attached on the smooth overturning wave meets the Gauss distribution.In addition,a superimposed overturning wave model is provided,which describes the phenomenon of “one wave after following another”.Three kinds of time-varying sea surface models with overturning wave are built at the same wind speed.3.The backscattering characteristics of time-varying overturning wave is simulated at the different incidence conditions and different wind speeds using Mo M method,and the eletromagnetic scattering from pure sea surface is analysed.The paper compares the scattering characteristics of three kinds of sea surface models combined the overturning wave crest and the pure sea surface,mainly aimed at the time-dependent characteristics ofdifference between the HH polarization and the VV polarization backscattering.Finally,the occurrence conditons and physical mechanism of the sea spike are alse summarised.4.Based on Mo M,firstly the Doppler Spectrum of pure time-varying sea surface is examined,and its main features are obtained.And the Doppler Spectrum of the sea surface combined overturning wave with high wind speed and S-band incident wave is compared with that of the pure sea surface,and the theory that how the single,superimposed and double overturning wave influences the Doppler Spectrum of pure sea surface is summarized at the aspects of Doppler broadening and Doppler frequency shift. |
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