以VBS RTK GPS輔助UAV熱影像定位定向之研究

Abstract

熱像儀獲取之地表溫度變化常反映地物重要資訊，若能提高其空間解析度，將可擴展其應用領域，故本研究嘗試以單旋翼無人機系統(Unmanned Aircraft System, UAS)酬載熱像儀，期更有效率地蒐集高解析度熱影像，供防災、環境監測使用。但熱控制點佈設不易，本研究欲以GPS輔助單旋翼UAS熱影像定位定向，降低地面控制點需求，故於UAS上加裝Trimble BD970 GNSS OEM接收模組，以VBS-RTK (Virtual Base Station -Real Time Kinematic, VBS-RTK) GPS定位技術，將GPS觀測資訊作為空中控制使用。但此需解決GPS天線相位中心與相機透視中心之偏移量(即GPS天線偏移量)的問題，故本研究基於光束法空中三角測量平差，視GPS天線偏移量為一定值，發展一數學模式，解決此偏移量的問題。此外，熱像儀屬於非量測型相機，本研究以野外率定場法，執行熱像儀率定，取得較精確之相機參數，供後續空中三角測量平差使用。 由模擬資料驗證本研究所發展模式之可行性，且得知GPS天線偏移量於具有其對應之觀測量約制且GPS觀測量精度高時，可成功解算GPS天線偏移量；而於真實資料中，因GPS觀測量精度不佳，即使有GPS天線偏移量觀測量約制，仍無法成功解算GPS天線偏移量，但其精度已經可供防災與監測之用。雖真實資料之GPS觀測量精度不佳，但於影像連結性佳之情形下，仍可達到有效之空中控制，降低地控點之需求。 Thermal infrared images can show the temperature change of objects that represent the significant characteristics; therefore they have been applied on many fields. With the development of UAS (Unmanned Aircraft Systems), the thermal infrared camera can be carried on the Helicopter UAS to collect thermal images with high resolution in a local area more efficiently. However, the ground control marks for thermal images are uneasy to be set up. In this study, the Trimble BD970 GNSS OEM board will be carried on the Helicopter UAS to collect GPS data by VBS-RTK GPS technique to support the bundle adjustment for the positioning and orientation of collected thermal images, i.e. AT(Aerial Triangulation). In theory, the GPS antenna offset is not changed and can be viewed as constant. Therefore, in this study, the new model based on bundle adjustment will be developed to solve GPS antenna offset, exterior orientation parameters and the object coordinate of tie points simultaneously by unified least squares adjustment. Besides, thermal infrared camera is a non-metric camera. In order to acquire high precision camera parameters for AT, thermal infrared camera will be calibrated by field method. In this study, the simulated tests verify the feasibility of the new developed model for GPS supported aerial triangulation and show that the GPS antenna offset can be solved based on the ideal accuracy of GPS observations and the observation constraint of GPS antenna offset. Due to the bad accuracy of GPS observations in real data collection, the GPS antenna offset can be not solved. Although the accuracy of GPS observations is bad, the GPS observations can also be used to support the bundle adjustment for the positioning and orientation of thermal images under better block geometry and ground control points still can be reduced.