空用脈衝普勒雷達海洋雜波模擬

Abstract

本篇論文旨在建立一個模擬空用脈衝都普勒雷達之海洋雜波之模型。要求出海洋雜波之雷達反射信號之頻譜，首先要考慮距離混淆(Range ambiguity)及都普勒頻率混淆(Doppler ambiguity)之影響，然後模擬出海洋反射係數之分佈特性以及天線增益圖形。 海洋雜波之雷達反射信號可區分為以下這二點：<1>其雷達反射信號之振幅機率分布可用偉伯(Weibul)機率分布函數來表示，而偉伯函數之形狀參數(shape parameter)呈相關於俯視角(grazing angle)之線性函數，<2>海洋雜波之平均單位面積雷達截面積(RCS)可藉由已知之量測資料展成一組相關於海浪級數及俯視角之多次函數。 本篇採用一個改良的距離都普勒格之面積計算方法，它將所有會發生之面積形狀考慮過後寫成一個完整之公式。由於這個方法不再需要運用數值積分方法去求這些多變形狀之面積，可大大的減低雷達模擬系統之計算負荷。 另外要求地面上任一塊區域所對應之天線增益，勢必要找出此區域相對於天線之球面座標。在本模型中天線之指向可任意改變。本文也建立一套座標變換方法來解決這個幾何問題。

The purpose of this thesis is to develop a sea clutter simulation model for airborne pulse-Doppler radar. Sea clutter characteristics has been reviewed. The amplitude statistics of sea backscattering is modeled by Weibull distribution with shape parameter linearly depends on the grazing angle. Using interpolation in least square sence on available data [10], the mean backscatter coefficient of sea is implemented by a set of polynomial functions of sea state and grazing angle. The problem for evaluating the size of range-Doppler cell of arbitrary shape is overcomed by using the closed-form expression developed by Jao and Goggins [8]. This method avoids the need of complicated numerical integration. Consequently, the computational load is greatly reduced. Also a coordinate transformation procedure is developed to determine the angular location of cell relative to the antenna beam axis. Our simulation model for the generation of sea clutter map is applicable for an arbitrary combination of radar pulse-Doppler waveform, platform velocity and altitude, and antenna pointing direction half power beamwidth and sidelobe level. The simulation result show the ability of calculating clutter return in altitude line, side lobe and mainbeam associated with arbitrary antenna orientation.