Electromagnetic Modeling And Measurement Of Scattering From Multi-scale Sea Surface

It is important to research the scattering from sea surface in the remote sensing of ocean,early warning,and target recognition.It also provides an important theoretical support and guidance to inverse the marine parameters,improve radar performance,and optimize the algorithm of target recognition.Echo from sea surface depends on sea condition,the radar system parameters and detect conditions.Sea clutter is non-Gaussian,non-stationary,and complex spatial distribution.Therefore,it is still a challenge to study the characteristics of the scattering from sea surface on high resolution at low grazing angle.This dissertation is mainly based on the experiment of scattering from wave tank and electromagnetic theory to establish scattering model from sea surface.Integral equation method,beam simulation method,and small slope approximation(SSA)are used to analyze the characteristics of the clutter amplitude and Doppler spectra.The main contents and innovations are as follows:1.The scale of sea wavelength and significant wave height is proved to be equivalent to the scale of sea condition.The error of backscatter coefficient is discussed by simulating scattering from sea surface with different permittivity at different frequencies.It is proved that the backscattering coefficient from rough surface satisfied scaled relationship by using Kirchhoff approximation(KA)and small perturbation method(SPM).Based on the geometric scale model and electromagnetic scale model,the feasibility of measurement the sea scattering characteristics of high sea condition in wave tank is proved.After calibrating the data from wave tank in anechoic chamber,the backscattering coefficient of different frequency,different polarization,and different sea condition can be obtained.2.It needs a large number of unknowns,when use numerical method based on integral equation method to calculate the backscattering from sea surface at low grazing angle.In the sparse matrix canonical grid(SMCG),the original full matrix equation is decomposed into a band matrix which represents strong interaction and a translating invariance matrix which represents the weak interaction part.This paper derived the third-order Taylor expansion of the weak interaction matrix incident by HH and VV polarization.It effectively improves the convergence of the iterative solution.Based on the correlation of two points on the surface and the attenuation of the Green’s function in dielectric medium,sparse matrix canonical grid and physics-based two-grid(PBTG)are used to reduce the number of unknowns.It makes possible to implement the electromagnetic scattering from large area at low grazing angle.A comparison of the absolute value of the backscattering coefficient shows the theory and experiment to be in good agreement.3.SMCG is used to solve problem of backscattering from two-dimensional dielectric sea surface.The numerical results of backscattering from two-dimensional sea surface can be obtained by using the fifth-order Taylor expansion of weak interaction matrix.Based on decomposition of the one dimensional beam,I proposed a two-dimensional sub-beam decomposition method of Gaussian beam.The scattering from one-dimensional sea surface is calculated by combination one dimensional sub-beam and one-dimensional integration equation method.The two-dimensional sub-beam and two-dimensional integration equation method are combined like that.After computation the backscattering coefficient,the sub-beam decomposition is proved to be correct.The sub-beam decomposition also provides a theoretical basis of domain decomposition,which can be used for parallel computation of the backscattering from large and complex sea surface.4.The numerical integral equation method is used to calculate the Doppler spectra characteristics of the linear and non-linear sea surface on different polarization and different incident angle.Because numerical integral equation method needs a large number of memory and long execution time for calculating the scattering from two-dimensional dielectric sea surface,SSA-II is used to solve this problem.The characteristics of Doppler spectra are analyzed.The results show that the width of Doppler spectra of nonlinear sea surface is broader than that of linear surface,and the nonlinearity of one-dimensional sea surface is more obvious than two-dimensional surface.The model of sea surface currents is established and calculated by SSA-Ⅱ for Doppler spectra.The results illustrated that the Doppler spectra is broaden significantly by introducing ocean currents.5.The CUD A parallel model based on double-layer vegetation is established.By using the registers for faster memory access,the shared memory for parallel reduction,the pipelined multiple-stream asynchronous transfer,the parallel random number generator and the CPU-GPU heterogeneous computation,we take advantage of the massively parallel computation capability of NVIDIA to achieve the speedup of 216-fold.By using Intel MKL DFT library and partition computation in spectra domain,the ocean model is parallelism.By blocking operation of matrix-vector multiplication,the performance of calculating scattering from sea surface is improved.