| In this thesis, according to the theory of electromagnetic wave scattering from complex environment and the principle of action and reaction, the properties of electromagnetic scattering field from oceanic surface and typical targets are investigated. Emphasis is put on studying the scattering from 1- and 2-D fractal sea surface, the scattering from the non-Gaussian rough sea surface, the Doppler spectrum of sea clutter, the composite scattering from several targets, as well as the interaction between 1-D sea surface and a target above it. The main works are as follows:Firstly, an improved 1- and 2-D fractal sea surface model is present for modeling the oceanic surface. The fractal spectrum of this new model satisfies the negative power law spectrum when the spatial wave number is larger than the fundamental wave number, whereas it takes the form of the positive power law spectrum. The spatial correlation function and the spectrum of this improved model show good agreements with those given in the literatures. Based on the Kirchhoff approximation, the scattering coefficient and the scattering intensity coefficient of the new model are derived and calculated.Secondly, based on the horizontal-and vertical-skewness of sea waves, a modified two-scale model has been developed for the non-Gaussian sea surface. A complementary term is added to the first-order scattering coefficient of classical SPM (small perturbation method), which is proportional to the surface bi-spectrum and critical for explaining the difference between upwind and downwind observations. Meanwhile, in the new modified model, the effects of the shadow function and the curvature of the surface on the scattering are also considered.Thirdly, the first-order small slope approximation (SSA-1) is applied to a rough sea surface with non-Gaussian statistics, for which the third- and the fourth-order statistics are taken into account in the calculation of the scattering coefficient. Meanwhile, the result of SSA-1 is accorded with that obtained by the geometrical optics theory for the case of the incident wave with high frequency.Fourthly, based on the 2-D ocean-like surface of linear model and the first-order SSA, the Doppler shift of the scattered echoes is derived and obtained. By employing the two-scale model of rough surface, a formula of the spectrum widening for the scattered field from the oceanic surface is also present. The numerical results evaluated by the formulae in this work are also compared with the simulated and the measured data, and the dependences of the Doppler shift and the spectrum widening on the parameters, suchas the wind speed, the frequency of the incident wave and the incident angle etc, are discussed. It is found that the formulae obtained in this research can be used to estimate the actual results.Fifthly, combined with the equivalence principle, the application of the reciprocity theorem to evaluate the composite scattered field from two adjacent targets is developed. In general, the first-order solution can easily be obtained by calculating the scatted field from isolated targets when illuminated by an incident wave. However, due to the difficulty in formulating the couple scattering field, it is impossible to find an exact analytical solution for the second-order scattered field. In this study, the second-order solution of electromagnetic scattering from two adjacent conducting/ dielectric objects is derived by employing the reciprocity theorem and this solution is simplified from the volume integral to the surface integral form by the equivalence principle. The relationship between the secondary scattering field from one target and the other is derived.Sixthly, using the reciprocity theorem in connection with the equivalence principle, the characteristics of the composite scattering field from two adjacent objects, such as two adjacent circular cylinders with infinite length, two adjacent spheres, are investigated. In addition, this method has been extended to evaluate the scattered field from several adjacent targets. The bi-static scattering pattern is discussed and the results are compared with those calculated by the Time Domain Integral Equation Method (TDIEM).Seventhly, based on the numerical method (MOM, MOMI) and the reciprocity theorem, the scattering field from a 2-D target, which is above a dielectric plane or a conducting rough sea surface, is evaluated. It is proved that the efficiency of the new method presented in this work is much higher than that of MOM. In addition, using PO approximation and Mie theory in connection with the reciprocity theorem, the electromagnetic scattering of a simple 3-D target, e.g., a conducting plate or a spherical particle, above a Pierson-Morkowitz sea surface is numerically simulated, and the properties of the Doppler spectrum for the scattering field are analyzed and discussed in detail.
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