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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/48000


    Title: 陸基LFM-CW 合成孔徑雷達系統運動補償之研究;Motion Compensation for a Ground-Based LFM-CW SAR System
    Authors: 王俊偉;Jung-Wei Wang
    Contributors: 遙測科技碩士學位學程
    Keywords: 運動補償;合成孔徑雷達;線性調變連續波;motion compensation;SAR;LFM-CW
    Date: 2011-07-26
    Issue Date: 2012-01-05 14:24:34 (UTC+8)
    Abstract: 合成孔徑雷達(Synthetic Aperture Radar, SAR)是一個全天候主動微波成像雷達。它利用微波信號傳播到目標物計算其回波延遲的時間獲得垂直軌跡方向的分辨率,平行軌跡方向的分辨率則是利用載具與目標物之間的都卜勒效應來判定入標物間相對的空間關係。以線性調變連續波(Linear frequency modulation continuous wave, LFM-CW)取代傳統脈衝波(Pulse)的雷達系統,有著體積小、重量輕、傳輸能量低的優勢,適合放置在地面和無人載具的短距離量測系統,但也因為其傳輸能量低的特性,探測距離也受到限制,適合用來做近距離量測。 理想的成像演算法是假定載具以恆定速度沿一直線運動。然而,實際上載具的運動並非理想狀況,因地面系統容易受到地形影響會造成載具的震動、速度控制、姿態變化,導致回波信號存在一個相位誤差。且因為運動在方位方向並非為一恆定速度,在成像演算法中方位方向壓縮的匹配濾波器(matching filter)會造成方位方向壓縮品質不好。因此為獲得高品質的雷達影像,必須校正系統的運動軌跡對雷達回波進行相位上的補償,將信號還原成理想假設,改善方位方向壓縮品質。 利用慣性測量裝置(Inertial Measurement Unit, IMU)放置在天線中心,記錄天線的運動軌跡,將運動軌跡分解成距離方向及方位方向,分別進行回波相位的補償。IMU提供三軸角速度陀螺儀、三個正交線性加速度計、三個正交磁性方位計和16bit A/D轉換器。應用三軸陀螺儀推算動態的角度變化與三軸的線性加速度計,得到的三個方向的加速度與姿態資訊進行載具距離方向位置與方位方向速度的補償,推導運動補償的演算法,以獲得高品質影像。 本研究利用數值模擬方位方向速度變化量及距離方向天線位移量的影響,與地面實驗測試相互驗證模型與演算法。由模擬及實驗中,當天線在距離方向的位移變化兩公分時,幾乎無法壓縮成像。當速度變化與載具平均速度的比值越大時,方位方向壓縮效果越差。套用路徑補償的演算法後,其PSLR(peak sidelobe ratios)大約落在4dB,有效提高方位方向的壓縮能力。 Synthetic aperture radar (Synthetic Aperture Radar, SAR) is an all-weather active microwave imaging radar. It transmits microwave signals toward the target on a moving platform and records the returned signals. Conceptually, the resolution along the transmission path is determined by the echo path delay time while the resolution along the moving track is resolved by the Doppler effect between SAR platform and the target objects. Compared to pulse wave radar, LFM-CW (Linear Frequency Modulation Continuous Wave) radar has advantages of compact size, light weight, and low energy transfer, among others, which are suitable for ground and unmanned platforms requirements.. Ideal imaging algorithm assumes the vehicle is moving at a constant speed and along a straight line. In practice the platform movement is subject to turbulence that causes vibration and perturbation in speed and attitude, in turn. resulting undesired phase noise in the returning signals and thus degrading the image quality. Hence, to achieve good quality of SAR image, the phase changes, due to system motion must be properly compensated. In this study, an IMU (Inertial Measurement Unit), consisting of a three-axis rate gyroscope, linear accelerometer, magnetic tap, and A/D converter, was installed at the phase center of the antenna to record the trajectory of the platform. By measuring the linear and angular acceleration and attitudes, a motion compensated LFM-CW SAR imaging algorithm was developed to produce high quality SAR image. Simulations and experiments at both C and K bands ground demonstrator are used to verify and validate the algorithm.
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