• 作者： 陳錕山
• 作者服務機構： 中央大學太空及遙測研究中心
• 中文摘要： 藉由蒙地卡羅模擬（Monte Carlo Simulation）電磁波散射的模式，可以分析雙態海洋雜訊的統計特性。在此只考慮非同調回波，強調的重點是天線照射區尺度對海洋雷達雜訊的影響。照射區尺度大小的定義是經由其與入射波長的比較得來，大致上可分為：大、中、小三種尺度。為了進行這項研究，採用適用於微波雷達散射的海洋波譜半經驗式，以模擬海洋面的波譜。結果共產生1100個樣本。利用標準動差法（Standard Moment Method)對散射場進行計算，且用最小平方法對大量的散射場資料及常用的統計模式進行處理，以求得最適合的統計模式。結果發現在背向方向上，場量區域內的訊號統計特性遵守Weibull模式。當照射區尺度增大時近似Rayleigh模式。此外，散射場強度的平均值及變異數減低。在前進方向上且方位角135度時，不論照射區尺度大小為何，Camma模式對回波有最好的匹配。當方位角轉到45度時，訊號的分佈接近Gaussian模式。若減小照射區尺度，即使在前進方向上Weibull式仍有良好的訊號分佈型態。在垂直的方向上，Weibull模式對雜訊有最好的描述。這篇論文提供這些觀測的理論基礎。
• 英文摘要： The statistical characteristics of bistatics sea clutter were analyzed by means of Monte Carlosimulation of EM wave scattering. Only the incoherent returns were considered. Particular attention wasgiven to the effects of the size of the antenna footprint illuminating the surface on sea clutter. Relativeto the incident wavelength, the footprint was roughly divided into three different sizes: small, mediumand large. To conduct the study, a semi-empirical sea spectrum suitable for microwave radar scatter wasused to synthesis a sea-like surface. As a result, 1100 ensemble samples were generated. Numericalcalculations of the scattered fields were then performed by using the standard moment method. A largenumber of ensemble samples of a scattered field were then collected, followed by a least square fit tocommonly used statistical models to find the best fitted model. It was found that in the backward direction,the signal statistics of the field envelope followed the Weibull model. It approaches Rayleigh when thefootprint size increased. In addition, the means and variance of the scattered field strength decreased.In the forward direction and with an orientation angle of 135°, the Gamma model best matches the returnenvelope regardless of the footprint size. As the orientation angle was switched to 45°, the signal distributionapproaches the Gaussian model. Reducing the footprint size, however, leads to the Weibull distributioneven in the forward direction. In the perpendicular direction, Weibull generally best describes the clutter.Rationale of these observations were given in this paper.
• 中文關鍵字： antenna footprint; radar sea clutter; Monte Carlo simulation
• 英文關鍵字： --