合成孔徑雷達可以全天候的觀測地球環境變化，因此使用合成孔徑雷達影像來做資料的分析與蒐集(例如:地質調查，國土監測，地形變遷，海洋污染…等)，有無法取代的優勢。 然而，精確的幾何校正和輻射校正在合成孔徑雷達影像處理上是很重要的步驟。本實驗室目前已分別發展出利用延遲器產生斜距方向的延遲點，或使用頻移器產生方位方向的移動點，來做為影像的幾何校正控制點與輻射校正參考點。 對於考慮成本、便利、效率的前提下，本研究將改良第二代使用類比延遲器產生斜距方向延遲點的主動式雷達校正器，改以FPGA來實現數位式的延遲器，得以產生不同的延遲時間點。由於產生的延遲點距離可隨自行調整，對於影像上的幾何校正有很大的幫助。最後再以c波段的ERS-2衛星做測試。 經由實驗結果得知，此FPGA電路已經可以產生一至六個任意時間延遲的校正點。除此之外，第二代類比式主動式雷達校正器時間延遲誤差約為30ns至50ns，而第三代數位式主動式雷達校正器時間延遲誤差約為10ns以內，且時間延遲與輸出功率穩定性也優於第二代類比式主動式雷達校正器。Synthetic aperture radar(SAR) is capable of observing the changes of the earth surface in all weather. It has a great deal of the advantages to analyze and to collect the information about the environment on the earth, such as geological survey, the movement of the surface of the earth, and the ocean polluted extent, to name a few. However the precise geometric and radiometric calibrations are the critical points for SAR image processing. Our team has developed the delay line and the multiplier to produce the shift points at range direction and azimuth directions respectively. For the consideration of costs, convenience and efficiency, the focus in this study is to design a digital delay in active radar calibrator that can produce equal distance point target responses that serve as control points for both geometric and radiometric calibrations, by using FPGA. Performance of the digital ARC is tested on C-band ERS-2 SAR image. From the experimental results, the FPGA circuit can produce one to six calibration points of any time delay . In addition, the time delay error of the second-generation analog devices active radar calibrator is about 30ns to 50ns while the third one is less than 10ns. And the stability of the time delay and output power in the third one are both much better than in the second one.
