| Research of electromagnetic scattering from the sea surface has been drawing more and more attention in complex sea condition, because of its wide applications to target identification and acquisition. However, it is in urgent to develop fast and effective numerical computation methods in electromagnetic scattering with more and more ocean engineering applications. The main contribution of this dissertation is the combination of the forward-backward method,the general forward-backward, the modified forward-backward and parallelism technology(Open MP) for scattering calculation of breaking waves in different stages and sea surface.to provide a efficient, quickly and accurate numerical solution to electromagnetic scattering calculation under complex sea conditions. And then a plain interpretation about mechanism of the “sea spikes” is given.In numerical calculations of my dissertation, the geometric modeling of sea surface and breaking waves, the choice of the tapper width g and surface length L and some basic parameters is key, so a brief introduction is given and a one-dimensional PM sea surface is numerical simulated by the Liner Filtering method. The matrix equations of FBM is derivate from the integral equation and is used to program FBM. Besides, through studying the FBM convergence properties which is unrelated the height variation of sea surface and only related with the type of integral equations and the incident frequency, the FBM maximum iteration times for the worst case is given. What’s more, a detail verification of FBM under different wind speed, the incident angles and the incident frequency is made by LU decomposition and the results agree wel.The matrix equations of MFBM are derivate from the double integral equations and is used programming MFBM. Again, the convergence properties are discussed. Besides, we parallelize the processes of the FBM and MFBM, including impedance matrix filling, triangular matrix multiplication and the solution of triangular matrix equation and the performance of different parallel schemes were discussed to give the best programs. By comparing the results of the FBM and MFBM, we discussed the FBM accuracy under different wind speeds, the incident frequency, where the incident wave frequency greater effect on the result of the FBM than the wind speed. And when the incident frequency is increased to a certain value, the root-mean-square error is too great to be ignored. The accuracy of FBM can be effectively improved through reducing the sampling interval. We introduced the experimental measurements at low grazing incidence angle which measured the NRCS of low-wind-speed PM surface generated by the wave pool in S and K u band. By comparing the FBM results with the experimental measurement results, we verify the FBM accuracy.Then, we inducted the he matrix equations loaded the impedance boundary. The RSC of breaking waves, conductor and dielectric plate were calculated. The calculation results of breaking waves indicated that the breaking waves can greatly enhance the backscatter. And with the development of the breaking waves, the effect is more and more obvious. What’s more, we studied the electromagnetic scattering of breaking waves and sea surface by GFBM and FBM. The results show that, compared with the VV polarization, the HH polarization is apt to the geometry construction of sea surface, the incident frequency and the incident angle. The bistatic scattering has been greatly strengthened both HH and VV polarization, especially HH polarization. Besides, the existence of breaking waves result in peaks and downs, and the existence of sea surface affect the peaks and downs. |
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