運用超高解析衛星進行疏濬高程控制可行性研究

Potential of Elevation Control in River Channel Dredging with Super High-Resolution Satellite Images

臺灣河川受地質及地形之影響，中下游土石堆積快速，常須經由適當的疏濬或河道整理以維持河川水文流徑並保障河道週邊生命財產安全，然而過去在疏濬工程過程中產生的有價土石常有違法的情事發生。為杜絕超深越界等情形，主管機關訂定相關機制做為防堵的手段，然而過程中仍須地面監測作為輔助資料。隨著遙測科技的進步，新一代次米級超高解析度衛星在軌道運行過程拍攝之立體像對，結合數值地表模型（digital surface model, DSM）產製技術，可解決傳統現地測量點狀施測需耗費較高的時間及人力成本，以及河道中高程落差大與砂質鬆軟區域難以量測之問題。因此本研究以高屏溪主要支流荖濃溪做為研究區域，採用超高解析度Pléiades衛星立體像對配合影像匹配技術產製數值地表模型，並以無人飛行載具系統（UAS）及地面高程測量所提供之獨立數據進行精度驗證，將Pléiades衛星及UAS產製DSM進行高程套合比對，探討其作為土方濬深高程控制檢核的依據，檢驗河川疏濬過程河道變化。在比對兩者所產製之DSM後，可計算Pléiades相對高程精度為0.70公尺。而經由主管機關提供的地面檢測，驗證Pléiades在河道斷面平均高程的相對精度為0.47－0.84公尺，控制精度約為衛星影像1－2像元。衛載遙測方式可有效率的產製面狀地形，彌補地面測量空間密度不足問題，故後續建議針對各大型疏濬區可辦理遙測方式配合地面測量，而達到實際監測之目的。

As formed by the steep terrain and fragile geological conditions, river channels in Taiwan have long been required to dredge deposited sand and gravel and to ensure the safety along the river banks. However, the dredging works are sometimes loomed by the alleged illegal operations including overstepping and over-dredging along the designated profiles. To prevent the illegal activity, remote sensing technology has a great potential to monitor the work. Spaceborne images are considered superior in coverage and efficient in contrast to conventional ground surveying. Hence, this study investigates the possibility of monitoring the dredging work by using satellite data. We analyze the temporal evolution of the digital surface model (DSM) through the super high-resolution Pléiades stereopairs, and examine the model accuracy by other data such as unmanned aerial system (UAS) DSM and ground measurements. The vertical accuracy of Pléiades DSM, as compared with UAS DSM and ground points, reaches 0.70 m and 0.47-0.84 m, respectively, which is about the order of 1-2 image pixels. We conclude that the spaceborne data is a feasible approach in company with ground leveling to keep track of the procedure of gravel removal works, especially for those large and remote areas.