由於合成孔徑雷達可以全天候的觀測地球環境變化，利用合成孔徑雷達影像作資料的蒐集與分析 (例如：變遷偵測、地物分類、國土監測) 有不可取代的優勢。然而要分析這些資料，影像的輻射校正是很重要的步驟，所以本論文發展C 波段可調式都卜勒頻移主動雷達校正器，針對歐洲太空總署(ESA)的兩顆合成孔徑雷達衛星ERS-2、ENVISAT，進行合成孔徑雷達影像校正。 本研究應用都卜勒效應研製C波段可調式都卜勒頻移主動雷達校正器，利用合成孔徑雷達信號做都卜勒頻移，產生方位方向的移位，作為影像方位方向的幾何校正控制點。經實驗證實，可以從影像中萃取合成孔徑雷達影像校正係數(K)值為54.24dB，且將合成孔徑雷達信號分別產生180 赫茲與240 赫茲的頻移，其空間的移動量分別為565.87 公尺與749.18 公尺,與理論值相符。由本研究發展的校正器可以得到兩個可靠的方位方向移動點，提供方位方向的幾何校正參考點，而獲得到的校正係數(K)值，可作為精密輻射校正之用。 Operating in all weather, the synthetic aperture radar(SAR) has great advantage to collect and analyze the earth environmental information,such as change detection, land cover classification, and land use monitoring, just to name a few. However, before these can be done, a precise radiometric calibration is critical. This study is devoted to developing a C-band tunable Doppler shift active radar calibrator for such purpose. The experimental measurements and tests were carried out by using SAR onboard ERS-2 and ENVISAT satellites. By shifting the frequency along the azimuth direction, it is possible to generate point response along that direction and hence provide good control points on the ground for both radiometric and geometric calibrations. Experimental data confirms that the calibrator constant, K, is about 54.24 dB for ERS-2 and ENVISAT SAR. The dual frequency shifts at 180 Hz and 240 Hz produce a spatial shift at 565.87m and 749.18m, respectively, which are in excellent agreement with theoretical values. Hence, the operational function of the developed calibrator is successfully demonstrated. It should be very useful to precise geometric and radiometric calibration for satellite SAR.
