The Research On FDTD Numerical Calculation From Rough Sea Surfaces And Its Application On Wind Speed Retrieving

With the development of marine radar remote sensing technology, the retrievalmethod of the sea surface wind speed parameter also has got deeper and further study. Butno one model function is the best for all of the sea conditions, and there is little modelfunction which is based on electromagnetic theory. In this paper, a number of attempts to aretrieval method of the sea surface wind speed which is based on the electromagneticscattering theory of random rough sea has been made. The specific content is to build arandom rough sea surface using the PM spectrum first, then using the finite-differencetime-domain (Finite Difference Time Domain, FDTD) method,radar backscattercoefficient of random rough sea surface (Normalized Radar Backscatting Cross-section,NRCS) is calculated, and finally using the results of the sea surface backscatteringcoefficient, the wind speed parameter is retrieved.Firstly, the paper summarizes the research progress of electromagnetic scattering ofrandom rough surface and the retrieval of sea surface wind speed of altimetry. And thefeasibility and significance of this study is demonstrated as well.Secondly, the basic principle of FDTD method is introduced in detail. It starts directlyfrom Maxwell’s curl equations to separate the variables using second-order centraldifference form, then take alternate sampling of each component of the electric field andmagnetic field components in space and time domain, then with updated of each time stepby step, the numerical electromagnetic field problem is solved. It also issues points thatare worth of notations in the analysis process of FDTD method, such as the basic iterativederivation and application methods, the introduction of electric flux density instead of theelectric field component, stability of the algorithm and numerical dispersion problems,etc.Then, the FDTD method is validated. The paper establishes a Gaussian randommedium rough surface using classical FFT methods.Then its electromagnetic scatteringvalues are calculated using the FDTD method. Through simulation by MATLABprogramming, the backscatter coefficient is obtained. By comparison with similar carried out studies, the paper verifies the feasibility and effectiveness of the FDTD method inrandom rough surface electromagnetic scattering problems.Finally, the FDTD method is applied to the retrieval of wind speed of sea surface. Inorder to get closer to the actual rough sea, the paper builds a model of sea surface usingthe PM spectrum. And using the FDTD method to establish the rough sea simulations, thebackscattering parameters is calculated. Then using the above backscattered parametersthe sea surface wind speed is retrieved. By comparison and analysis of the FDTD methodto retrieve sea surface wind speed and the existing available model functions of seasurface wind speed retrieval, in this paper, the results are generally consistent with trendsand empirical model function and in7-10m/s wind speed region the results are in goodagreement. But because the retrieval is only simply based on the backscattering coefficient,there existing a larger error in low wind and high wind area. So the method needs to beimproved.In this paper, study of the retrieval method of wind speed for satellite radar altimeterbased on random rough sea surface electromagnetic scattering model is illustrated. And ithas certain reference value for the future retrieval algorithm research of sea surface windspeed.