Charecteristics Analysis And Modeling Research On Electromagnetic Scattering From3D Complicated Rough Sea Surface

The research on electromagnetic (EM) scattering from the randomly rough seasurface is of great theory value and application prospect in many fields such as seamicrowave remote sensing, radar guidance and acquisition, radar target recognizing andfeature extraction. How to efficiently simulate the EM scattering characteristics of3-dimensional (3D) dielectric rough sea surface has been a hot topic in real engineeringapplication. The emphases of this paper are concentrating on its own characteristics ofEM scattering and relevant methods, especially majored on the computational problemsrelated to the scattering from sea surface and the composite scattering from roughsurface and above target using the analytical methods, numerical methods and thehybrid method. The main contents are as following.1. The basic theories and some issues of concern in the sea scattering have beenintroduced. In term of radar equation, the scattering coefficient of extended roughsurface and the parameters of2-dimensional (2D) tapered incident wave were studied.Then, we gave the relationship between electrical characteristics of seawater andfrequency, temperature, salinity based on the Debye model. At last, several typicalgeometry structures of the different sea states, including the wind-driven sea, internalwaves and breaking waves, were modeled in this paper.2. The comprehensive studies of the local forward-backward iterative physical optics(LFBIPO) and its optimization techniques were carried out. The application of physicaloptics (PO) based on the frequency domain integral equation has been applied in thescattering anlysis of relatively flat rough surface. In order to deal with the scatteringproblem of rougher surfaces, the iterative PO (IPO) was introduced to analyze the EMcoupling effects among the sea surface elements. Some experiments showed that thehigher computational accuracy was achieved without the extra computational costs.Meanwhile, the forward-backward methodology (FBIPO) and its modification withunder-relaxation iterative method were employed to speed up the convergence of thecommon IPO. Then, based on the scattering characteristics of rough surface, the farfield approximation (FaFFA) and local iteration methodology were proposed to reducethe computational complexity and further improve the efficiency in each iterationprocess. At last, the scattering analysis for the rough surfaces with different roughnessand permittivity were investigated according to the above methods. 3. The principle of multilevel fast multipole algorithm (MLFMA) and its applicationsin the EM scattering from sea surface have been studied. Firstly, the framework inMLFMA has been introduced and its aggregation and disaggregation terms werededuced based on the impedance boundary condition (IBC). Secondly, some specialtreatments were analyzed, including the truncation parameters of sea surface, edgeeffects control. Thirdly, some optimization techniques were also adopted, including theadaptive higher order hierarchical Legendre basis functions to reduce the number ofunknowns, sparse approximation inverse (SAI) precondition for the efficient solution oflarge-scale problems,3D Fourier fast transform (FFT) to accelerate the solution in thetransformation operator. Finally, the EM scattering of time-evolving breaking waveswere simulated numerically at the low grazing angles (LGA), and its scatteringmechanism of the sea spike phenomenon and Doppler shift/splittng effects in the radarecho have been validated and explained in this paper. The numerical studies in this fieldcan provide requisite reference data.4. The bi-iteration model was proposed to analyze the composite scattering betweenrough surface and target.The hybrid method combining the PO/FBIPO and MLFMAwas applied to solve scattering of the rough surface and target, respectively, and theiteration process was utilized to analyze the EM coupling effects between them. For thedifferent roughness of rough surface, the relevant truncation rules of rough surface andanalytical methods were discussed to reduce maximum the computational complexity.Furthermore, aiming at the efficiency, the FaFFA technique was also used to speed upthe interaction process between rough surface and target.5. According to the quasi-stationary algorithm, the series of time domain radar echowere acquired for the time-evolving sea surfaces using the frequency domain methods.Then, the Doppler shift and Bragg scattering for the simple dynamic sea surfaces havebeen analyzed using a standard spectral estimation technique. The typical scatteringphenomena in engineering experiments were reoccurred by the electromagneticnumerical simulations.The studies demonstrate the efficiency of the several proposed methods in the EMscattering of3D rough sea surface. The analysis and the numerical results in this papercan provide the physical mechanism explanations in the scattering from rough surfaceand valuable data in the electromagnetic simulation engineering.