根據水保局最新的統計資料,全臺灣有1705條土石流潛勢溪流,遍佈159個鄉鎮,做好土石流防災預警工作有著非常重要的意義。現有的土石流監測站均安裝有固定式的室外監控攝像機,但這些攝影機只能回傳影像供學者後續研究使用,還不具備監測預警功能(例如自動判別土石流和計算流速等)。本研究旨在探索一種適合土石流現場流速計算的方法,研究重點在於使用現有的監控攝像機恢復圖像實際的三維資訊,後續再結合LSPIV技術實現土石流監測預警。本文主要的研究方法是使用光學變焦相機,通過變化兩個焦距恢復圖像的實際三維座標,再利用粒子追踪測速技術計算流體的表面流速。 研究的內容包含以下幾點:第一,比較基於點和基於面積的變焦測距實驗,發現基於面積的變焦測距方式結果更加穩定,適合實際應用;第二,利用變焦技術恢復了圖像的中幾個參考點之後,結合影像處理的方法計算的實驗水槽中流體的表面流速,平均誤差在10%之內;第三,設計一套適合現場使用的參數檢定實驗,獲得相機的內外參數矩陣,計算結果較為可靠。 本研究的意義在于土石流發生時,河床高層變化顯著,原有的參考點坐標被破壞,變焦的方式可以實時更新現場目標的三維資訊。通過以上的研究內容,初步驗證變焦測距應用於表面流速測量具有一定的實用性,但是本研究還未能真正應用在土石流監測現場,這也是未來需要努力的方向。
According to the latest statistics of the Soil and Water Conservation Bureau, there are 1705 potential debris flows in Taiwan, all over 159 villages and towns, so it is very important to do a good job in disaster prevention and relief work. The existing earthwork monitoring stations are equipped with fixed outdoor surveillance cameras, but these cameras can only return images for follow-up study of the use of experts, do not have the ability to monitor and warning (such as automatic identification of debris flow and the flow rate, etc.). The purpose of this study is to explore a method for calculating the flow velocity. The research focus is to use the existing zoom cameras to restore the physical three-dimensional information of the image, and then follow the LSPIV technology to realize the monitoring of debris flow. The main method of this paper is to use the optical zoom camera to restore the physical three-dimensional coordinates of the image by changing two focal lengths, and then use the particle tracking velocity technique to calculate the surface velocity of the fluid. The results of the study include the following points: First, comparing the point-based and area-based depth measurement experiments, it is found that the area-based method is more stable and suitable for practical application. Second, using zoom technology to restore the three-dimensional information of the image, the surface velocity of the fluid in the experimental tank calculated by the method of image processing and the average error is within 10%, Third, a set of parameter calibration experiment is designed for calculating the camera's internal and external parameters matrix, and the results are reliable. The significance of this study is that when the debris flow occurs, the elevation of the riverbed changes significantly, then the original reference point coordinates will be destroyed, and the method of changing focus can update the three-dimensional information on the scene real-timely. Through the research, it is proved that applying depth estimation of the zoom images on surface velocity calculation is practical, but the research has not been applied to the monitoring site of the earth flow yet. This is also the future research direction.
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