一般高地面解析影像要能充分發揮其實際的應用功能，其輻射的品質扮演極重要的角色。福爾摩沙五號衛星(福衛五號)已於2017年8月發射升空，其主要的光學遙測酬載為資源遙測應用的高地面解析遙測儀器(Remote Sensing Instrument，RSI)。福衛五號在升空後一年內RSI的輻射參數明顯變化，為維持RSI之輻射品質，定期得在軌絕對輻射校正極其重要；另一方面，根據前期的校正結果，特定目標輻射校正與相互輻射校正間仍有差異存在，對於輻射校正係數之選用尚其不確定因素有待釐清。為達成提供高品質影像資料之目標，本研究將藉由衛星與地面同步量測實驗，檢驗並整合輻射校正方法，研擬最佳之福衛五號在軌輻射校正作業方法與程序，包括特定目標輻射校正 (vicarious calibration)與相互輻射校正 (cross calibration)，針對福衛五號RSI進行密集在軌絕對輻射校正掌握儀器輻射特性變化，以期維持福衛五號觀測影像之輻射品質。校正結果顯示，兩種方法之校正結果相當一致，且所獲之RSI輻射轉換係數在升空後持續地變化，與發射前之相對差異在可見光頻道達27%；全色態頻道達22%，各頻道彼此間的相對差異約5-8%，相較於2017年校正結果相對穩定。此外，本研究結果亦確認特定目標法的主要不確定因素來自於大氣氣膠光學參數。;FORMOSAT-5 (FS-5), launched in August 2017. The main payload onboard is optical sensor named Remote Sensing Instrument (RSI). The radiometric sensitivity of a new optical sensor may be unstable especially during the first year after launched. Therefore, the on-orbital absolute radiometric calibration is essential and significant to maintain the image quality of optical sensor, which is the main aim of this study. Two on-orbital radiometric calibration approaches, vicarious and cross calibration, are examined by field campaigns on the calibration sites. The ground-based measurements of atmospheric parameters and surface reflectance are primarily collected for vicarious calibration, while the reference images from Landsat-8 Operational Land Imager (L-8 OLI) are employed for cross-calibration. The derived calibration coefficient of RSI spectral bands are based on the near simultaneous observations between the received radiance on the top of atmosphere, FS-5 RSI and L-8 OLI spectral digital numbers. The results indicate that the variation of optical sensitivity of RSI are obvious after launched. The calibration coefficient in each band has no evident consistency in 2017, but it tends to stable on the order of 5-8% of variation for most part of spectral bands in 2018. The results of calibrations indicate that the atmospheric environment should be taken into account, especially the aerosol optical depth. The results also suggest that the periodical calibration is necessary and very important to the further scientific applications.
