應用光達系統於林道土壤沖蝕監測之研究-以小關山林道為例

本研究使用手持式光達掃瞄系統，運用其掃瞄技術，實測製作3D點雲模型資料，建立數值高程模型套疊，並針對小關山林道所設置之樣區，進行土方量驗算，並另用不安定指數與地理資訊系統，配合各項沖蝕因子，包括坡度、坡向、地形濕度指數、坡度粗糙度與坡向粗糙度，計算各因子指標權重值，繪製小關山林道沖蝕潛勢圖，最後再以地面光達作為對照組，將兩種光達之三維點雲資料進比較，瞭解手持式光達系統應用於土壤沖蝕與土方量測量之可行性，根據結果顯示手持式光達以及地面光達兩者所量測結果之差值皆於2 cm以內，精度誤差平均為0.86 %，在土方量計算方面，小關山第98林班之林道總沖蝕與堆積土方為63.97 m3與26.95 m3，而小關山第102林班之林道總沖蝕與堆積土方為40.37 m3與93.78 m3，兩者之土方變化量各為37.02 m3與53.41 m3，總體而言小關山第102林班之林道土方堆積量高於第98林班之林道，推測原因可能為第102林班之林道上方邊坡上地表植被較為稀疏，也無高大之喬木阻擋雨滴造成之沖蝕，因而造成大量土方被搬運到下方林道堆積。在沖蝕潛勢圖分析結果得到小關山第98林班之林道使用因子為坡度、坡向、地形濕度指數、坡度粗糙度與坡向粗糙度，低潛勢及中低潛勢區所占比例較高，共佔總網格數比例67.45 %，而在中高潛勢與高潛勢地區在總網格數比例佔了11.69 %。

關鍵字

光達掃瞄系統；林道沖蝕；土方量；不安定指數

並列摘要

This study uses a Hand-held Mobile LiDAR Scanner (HMLS) for data scanning and building and the making of 3D point cloud model to create a numerical terrain model and perform earthwork analysis within Xiao Guan Shan forest trail plots. The instability index with various erosion factors was analyzed in geographical information systems, including slope, aspect, topographic wetness index, slope roughness, and aspect roughness. The weights of each factor and the potential erosion of Xiao Guan Shan forest trails were established. TLS was used as the control group, and two kinds of 3D point cloud data were compared to understand the feasibility of the HMLS applied to soil erosion and earthwork measurement. According to results, the difference between the measured results of the HMLS and the TLS is less than 2 cm, and the accuracy error is 0.86 % on average. In terms of earthwork, the total erosion of the forest trail in the 98th forest class of Xiao Guan Shan. The accumulated earthwork is 63.97 m3 and 37.02 m3, while the total erosion and accumulated earthwork of the 102nd forest class of Xiao Guan Shan are 40.37 m3 and 93.78 m3, and the earthwork variation for the two forest class is 37.02 m3 and 53.41 m3, respectively. The earthwork accumulation of the forest trail in the 102nd forest class is higher than that of the 98th class. The sparse surface vegetation on the slope above the forest trail of the 102nd forest class and a lack in larger trees to block the erosion caused by raindrops leads to a larger amount of earthwork is transported to lower forest trail. Results of susceptibility analysis, factor of slope, aspect, topographic wetness index, slope roughness, and aspect roughness of the Xiao Guan Shan forest trails were taken into account, which the low susceptibility and moderately-low susceptibility accounts for 67.45% of total grids, in the moderately-high susceptibility and high susceptibility accounts for 11.69% of total grids.