Duan Zhugeng, Zhao Dan, Zeng Yuan, Zhao Yujin, Wu Bingfang, Zhu Jianjun
Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China.
School of GeoSciences and Info-Physics, Central South University, Changsha 410083, China.
Sensors (Basel). 2015 May 26;15(6):12133-55. doi: 10.3390/s150612133.
Topography affects forest canopy height retrieval based on airborne Light Detection and Ranging (LiDAR) data a lot. This paper proposes a method for correcting deviations caused by topography based on individual tree crown segmentation. The point cloud of an individual tree was extracted according to crown boundaries of isolated individual trees from digital orthophoto maps (DOMs). Normalized canopy height was calculated by subtracting the elevation of centres of gravity from the elevation of point cloud. First, individual tree crown boundaries are obtained by carrying out segmentation on the DOM. Second, point clouds of the individual trees are extracted based on the boundaries. Third, precise DEM is derived from the point cloud which is classified by a multi-scale curvature classification algorithm. Finally, a height weighted correction method is applied to correct the topological effects. The method is applied to LiDAR data acquired in South China, and its effectiveness is tested using 41 field survey plots. The results show that the terrain impacts the canopy height of individual trees in that the downslope side of the tree trunk is elevated and the upslope side is depressed. This further affects the extraction of the location and crown of individual trees. A strong correlation was detected between the slope gradient and the proportions of returns with height differences more than 0.3, 0.5 and 0.8 m in the total returns, with coefficient of determination R2 of 0.83, 0.76, and 0.60 (n = 41), respectively.
地形对基于机载激光雷达（LiDAR）数据的森林冠层高度反演有很大影响。本文提出了一种基于单木树冠分割来校正地形引起的偏差的方法。根据数字正射影像图（DOM）中孤立单木的树冠边界提取单木的点云。通过从点云高程中减去重心高程来计算归一化冠层高度。首先，对DOM进行分割以获得单木树冠边界。其次，基于这些边界提取单木的点云。第三，从通过多尺度曲率分类算法分类的点云中导出精确的数字高程模型（DEM）。最后，应用高度加权校正方法来校正地形效应。该方法应用于在中国南方获取的LiDAR数据，并使用41个实地调查样地对其有效性进行了测试。结果表明，地形影响单木的冠层高度，表现为树干下坡侧升高而上坡侧降低。这进一步影响了单木位置和树冠的提取。在坡度梯度与总回波中高度差大于0.3、0.5和0.8 m的回波比例之间检测到强相关性，决定系数R2分别为0.83、0.76和0.60（n = 41）。
