Study on Using Thermal Image to Establish Digital Surface Temperature Model

熱影像可獲取不同於可見光與近紅外光的溫度資訊，可運用於監測地表火山及斷層帶的溫度或災害防治上。以往於空載或衛載上的熱感測器解析度皆較低，判釋熱影像受到限制；如今，低成本、高機動性的無人飛行載具發展趨於成熟，可搭載熱感測器，並近空垂直拍攝近景熱影像，得到較高空間解析度之熱影像。 然而，熱影像上之地物內容與邊緣較一般可見光影像模糊，若要將熱影像應用於地理空間資訊系統上時，為使熱影像可與其他地面坐標資料結合，勢必需先幾何改正熱影像，並以相同區域之數值地表模型，正射化熱影像，同時三維展示熱影像與地表模型，提供研究者地形與熱分佈資訊；此外，對於火山地帶來說，高程資料也常是研究者判釋分析的重點資訊，此做法可看出區域之溫度分佈。 為正射糾正熱影像，利用共線式執行空中三角測量平差，本研究不僅率定熱像儀，求其內方外元素，更以空中三角測量平差，計算熱影像之外方位元素。此外，因熱影像紀錄地表輻射資訊，與可見光資訊大不相同，故熱影像經共線式空中三角測量平差後，建製之數值地表模型 (Digital Surface Model, DSM)，並非該拍攝地區之真實地表起伏模型，因此本研究利用一既有的DSM，正射糾正空中三角測量後之熱影像，並以誤差向量圖表示正射糾正之成果。Usually, thermal images contain abundant temperature information which can often be used to monitor the surface temperature or volcanic disaster prevention. Previously, thermal images acquired by satellite platform have low resolution. Today, low-cost, highly maneuverable unmanned aerial vehicle (UAV) can carry thermal sensors and obtain close-range thermal images with high spatial resolution. Due to the distortion of thermal sensor, geometric correction should be applied to the thermal images. In this study, a UAV-borne thermal sensor has been calibrated, and used for taking thermal images. The exterior orientation elements of the thermal images have been determined by using aerial triangulation. A digital surface model generated by LiDAR was then used to ortho-rectify the thermal images. Gray values of the rectified thermal images were also normalized for generating a thermal mosaic. The resultant rectified thermal mosaic has excellent appearance for showing the temperature distribution and elevation simultaneously