河川礫石之幾何形狀與排列方式影響河道中的水流運動，對於生態復育與瞭解河川輸砂能力具有重要意義。本研究利用地面光達可快速量測地物三維空間坐標之特性，以台北新店溪一裸露砂洲為實驗區，分析裸露砂洲之二維碎形幾何特性。
　　本文首先探討地面光達產生之數值高程模型與斷面尺量測(地真)之相關性，並針對不同取樣區塊大小(2m×2m 與6m×6m)之數值高程模型資料作空間統計之分析，最後討論地面光達測站之擺設及數目，以提昇整體外業作業效率。
　　研究結果顯示，光達確實可快速提供河床礫石之三維空間資料，相較於傳統的斷面尺量測的線型結果更具完整的空間描述。值得注意的是，光達資料必須經過濾除作業再網格化產生數值高程模型，以減少光達資料的誤差影響。本研究中考慮之取樣區塊大小之測站架設，小範圍(2m×2m)於grain 尺度光達掃瞄測站組合不可少於六測站組合，而form 尺度最少可使用二測站組合進行掃瞄，大範圍(6m×6m)因距離較遠及遮蔽問題之影響，需要位於角落之四測站結合資料。

　　The water flow field is significantly affected by the geometrical shape and formation arrangement of gravels, that makes up the river bed, both are important for ecology restoration and sediment transportation.
　　In this study, we employ the ground-based lidar (Light Detection and Ranging), which is able to provide rapid 3D information of the gravel bed surface, and conduct 2D fractal analysis on a gravel bar in Sindian rive of Taipei. Ground truth data are collected by the method of manual profiling at 1cm interval. The spatial statistical analyses are conducted on different patch sizes: 2m×2m and 6m×6m.
　　The results show that the correlations between the lidar derived DEM (Digital Elevation Model) and the manual profile data are high. The lidar DEM provides more detailed 2D fractal parameters than the traditional manual profiling method with the complete description of spatial continuity. It is found that the lidar data need to be filtered before they can be used for fractal analysis. It is also found that 2m×2m patch can use the different scan station number under the different scale consideration, and 6m×6m patch can be completed by four lidar scans.

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