An improved topographic mapping technique from airborne lidar: application in a forested hillside

Abstract

We developed a robust method to reconstruct a digital terrain model (DTM) by classifying raw light detection and ranging (lidar) points into ground and non-ground points with the help of the Progressive Terrain Fragmentation (PTF) method. PTF applies iterative steps for searching terrain points by approximating terrain surfaces using the triangulated irregular network (TIN) model constructed from ground return points. Instead of using absolute slope or offset distance, PTF uses orthogonal distance and relative angle between a triangular plane and a node. Due to this characteristic, PTF was able to classify raw lidar points into ground and non-ground points on a heterogeneous steep forested area with a small number of parameters. We tested this approach by using a lidar data set covering a part of the Angelo Coast Range Reserve on the South Fork of the Eel River in Mendocino County, California, USA. We used systematically positioned 16 reference plots to determine the optimal parameter that can be used to separate ground and non-ground points from raw lidar point clouds. We tested at different admissible hillslope angles (15° to 20°), and the minimum total error (1.6%) was acquired at the angle value of 18°. Because classifying raw lidar points into ground and non-ground points is the basis for other types of analyses, we expect that our study will provide more accurate terrain approximation and contribute to improving the extraction of other forest biophysical parameters.

Acknowledgement

We gratefully acknowledge the use of lidar data sets supplied by Dr William E. Dietrich and the National Center of Airborne Laser Mapping (NCALM). J.H. Lee was funded by the W.S. Rosecrans Fellowship, Environmental Science, Policy, and Management, University of California, Berkeley. Dr Joshua B. Fisher contributed to this paper through work in the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.