Estimating Vertical Leaf Area Density Profiles of Tree Canopies Using Three-dimensional Portable Lidar Imaging

In this paper, a new method for estimation of vertical leaf area density (LAD) profile of tree canopy using portable scanning lidar is proposed. In this method, which we refer to as the voxel-based canopy profiling (VCP) method, several measurement points surrounding the canopy and optimally inclined laser beams are adopted to facilitate full laser beam illumination of whole canopy up to the internal. After the scanning, each data obtained from each measurement point are co-registered and the 3-D information is reproduced as the voxel attributes in the 3-D voxel array. Based on the voxel attributes, contact frequency of laser beams on leaves is computed and LAD in each horizontal layer is obtained. In addition, influence of non-photosynthetic tissues and leaf inclination angle on the LAD estimation are corrected. Using the method, good agreement between estimated and actual LAD was obtained in an individual tree of Camellia sasanqua. Next, the method was applied to broad leaved woody canopy of Japanese zelkova (Zelkova serrata (Thunb.) Makino). In the experiment, LAD profiles had different accuracy depending on each quadrat established on the measurement plot and on the laser incident angles. From the results, it was shown that the number of laser beam incidences N and G(c) (the mean projection of a unit leaf area on a plane perpendicular to the direction of the laser beam) are the factors to influence the accuracy of LAD estimation.