Research On Characteristics Of Radar Echo From Sea Surface Based On Electromagnetic Simulations

The radar echo from sea-surface contains rich information of sea. Studying its characteristics is not only helpful to obtain sea state information from the echo, but also useful to improve the ability of radar detection in sea clutter. Therefore, the research is very important whether in civil or military field. This paper studies the characteristics of the sea-surface scattering signal by utilizing electromagnetic simulation, with which can obtain comprehensive information of the oceanic conditions and the radar parameters. For the high acquisition cost and incomplete scene coverage of the experimental data, electromagnetic simulation can be a good complement and lay a solid foundation for summarizing laws of sea clutter.The research contents of the paper is organized with four parts:1. In order to solve the problem of dynamic sea-surface geometry modeling in electromagnetic simulation, the spectral method that only generates static sea-surface is improved by adding a time factor with which the time varying dynamic sea-surface can be obtained. The linear filtering method that quickly generates the sea-surface plays an important role for improving the efficiency of the large scale sea-surface simulation. Since the Pierson-Moscowitz spectrum only reflects the deep sea and fully developed state of sea-surface, the Wen spectrum with more parameters is introduced to better describe the sea growth process and the influence of sea depth.2. Considering the efficiency and accuracy in the electromagnetic scattering computation of electronically large size sea-surface, this paper studies the scattering models based on the inner scattering mechanism of sea-surface first. Secondly, the advantages and disadvantages of the approximate and the numerical methods on the electromagnetic scattering computation of sea-surface are compared. Utilizing the multilevel fast multipole algorithm with high accuracy as a reference, the scope of the application of the physical optics method is decided. With the sensible accuracy, physical optics method is applied for reducing considerable computation burden.3. To solve the problem of the sea clutter generation, the quasi-static method with complete physical meaning is utilized to simulate the time series of sea clutter, also the selection of time interval is decided. By exploring the standard spectral estimation method, the Doppler spectrum of sea clutter in different oceanic conditions and radar parameters is obtained from the simulated sea clutter sequences. Moreover, some important conclusions of the Doppler spectrum are summarized with considering of the influence of frequency, wind speed, wind direction,wind area and incidence angle.4. To analysis the statistical characteristics of sea clutter, sea clutters in different oceanic conditions and radar parameters are simulated with the quasi-static method and the rules of their amplitude distribution are summarized. Separately, the amplitude distribution is fitted with the common Rayleigh distribution, Log-normal distribution, Weibull distribution and K-distribution. To eliminate the non-stationarity of sea clutter, the amplitude difference of sea clutter is calculated to study its distribution laws changing with oceanic conditions and radar parameters. Then, the Tsallis distribution is introduced to fit amplitude difference distribution. Finally, the K-S test method is utilized to evaluate the fitting error of each distribution. By studying the laws about the optimal distribution changing with oceanic conditions and radar parameters, the paper reports that the Tsallis distribution is a reasonable distribution for sea clutter in different conditions.