title: Assessing and correcting topographic effects on forest canopy height retrieval using airborne LiDAR data.
abstract: 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.
authors.affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. zjj@mail.csu.edu.cn.|School of GeoSciences and Info-Physics, Central South University, Changsha 410083, China. zjj@mail.csu.edu.cn.|School of Sciences, Central South University of Forestry and Technology, Changsha 410004, China. zjj@mail.csu.edu.cn.
authors.forename: Zhugeng
authors.initials: Z
authors.lastname: Duan
authors.affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. zhaodan@radi.ac.cn.
authors.forename: Dan
authors.initials: D
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. zengyuan@radi.ac.cn.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. zhaoyj@radi.ac.cn.
authors.forename: Yujin
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth (RADI), Chinese Academy of Science, Haidian District, Beijing 100094, China. wubf@radi.ac.cn.
authors.forename: Bingfang
authors.initials: B
authors.lastname: Wu
authors.affiliation: School of GeoSciences and Info-Physics, Central South University, Changsha 410083, China. zjj@mail.csu.edu.cn.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Zhu
keywords: Dinghushan National Nature Reserve; LiDAR; canopy height point cloud; multi-resolution segmentation; topography