| In this paper the theories of the electromagnetic scattering of rough surface such as the Kirchhoff Approximation, the Phase Perturbation Approximation and the Small Slope Approximation are introduced. And the results of above three methods are compared with each other and also the data of the reference. The effective regions of the three methods and other methods are given.The 2-D ocean surfaces with PM spectrum and JONSWAP spectrum are simulated. The conventional two-scale model is modified to calculate the electromagnetic scattering from 2-D rough ocean surface. The slope of large roughness is obtained numerically. For large incident angle,the Z-BUFFER method is applied to calculate the shadowing function and the curvature effect of large roughness is taken into account. By contrast with experimental data,it can be concluded that the modified two-scale model is effective.The model of volume scattering of the whitecaps is given, and the variety of the microwave reflectivity with the thickness of whitecaps is calculated. The coverage of the deep ocean whitecaps is given with the formula of the whitecaps coverage with JONSWAP spectrum. The backscattering coefficient of the ocean surface with a slap of the whitecaps is calculated with the VRT, and compared with the result of the modified two-scale method.The signals scattered from the ocean surfaces are obtained by the calculations of EM scattering from 2-D dynamic PM spectrum ocean surfaces in X-band and Ku-band. Then a statistical test to identify the distribution among the Rayleigh, Lognormal, Weibull and K-distribution families which best fits to the datum of amplitude of clutter is derived. The power spectrum density of the experiment datum is calculated. With the method of the Daubechies wavelet, the noise of the experiment datum from the target time series under the sea background is cleaned out, and the effect of false alerting signal is reduced. |
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