Analysis Of Electromagnetic Scattering And Clutter Characteristic From 2-D Sea Surface With Two-scale Facet-based Model

Electromagnetic scattering from two-dimensional sea surfaces at high microwave frequencies is mainly based on the linear conditions. Simple filtering or superposition neglects the interaction of different components of the linear case. The actual sea-surface is the combination of all kinds of interactions which have a certain influence on the model itself and the properties of subsequent electromagnetic scattering. Thus, studying the scattering of two-dimensional nonlinear sea surfaces in this frequency band is very important.In this paper, the effect of nonlinear interaction on the electromagnetic scattering for two-dimensional cases at high microwave frequencies is analyzed using three parameters, namely, scattering coefficient, Doppler spectrum and the amplitude and amplitude ratio of the sea clutter. Numerical analysis of these parts is realized based on the establishment of a sea-surface model. Specific work is as follows:The method and step for establishing the linear sea-surface model based on the spectrum is introduced, and a relatively simple nonlinear model(Creamer) is obtained by improving and optimizing the linear model. The two kinds of surfaces in same conditions are compared in detail. The modified two-scale method, which is a conventional calculation method for electromagnetic scattering, is briefly introduced. This method is based on Kirchhoff approximation and small perturbation method. The influence of the curvature correction factor is also introduced. Calculation of scattering coefficients of the aforementioned two surfaces in the same condition using the modified two-scale method is presented.This paper briefly introduces the facet-based model method based on the two-scale theory. The derivation of the formula to obtain the scattered field for the two kinds of components is described. The hypothesis of the nonlinear effect on large-scale components is proposed to realize the modulation of the small-scale part. Thus, the sea clutter of the two kinds of sea surfaces at the X-band is obtained. The difference in Doppler shift and broadening of the Doppler spectra of the two kinds of clutter under different polarizations, wind speeds and wind direction are also calculated.Several relatively mature sea clutter distribution models are introduced. The sea clutter obtained by the above method is discussed in terms of amplitude and amplitude ratio. Statistical and parametric analysis of the sea clutter distribution model is performed under different physical parameters. Then, the influences of semi-nonlinear assumption on the statistical parameters of amplitude and amplitude ratio are compared. Finally, the modulation on the small-scale micro-rough structures of the large-scale components caused by the semi-nonlinear hypothesis is analyzed.