Estimation of vertical plant area density profiles in a rice canopy at different growth stages by high-resolution portable scanning lidar with a lightweight mirror

We used a high-resolution portable scanning lidar together with a lightweight mirror and a voxel-based canopy profiling method to estimate the vertical plant area density (PAD) profile of a rice (Oryza sativa L. cv. Koshihikari) canopy at different growth stages. To improve the laser's penetration of the dense canopy, we used a mirror to change the direction of the laser beam from horizontal to vertical (0 degrees) and off-vertical (30 degrees). The estimates of PAD and plant area index (PAI) were more accurate at 30 degrees than at 0 degrees. The root-mean-square errors of PAD at each growth stage ranged from 1.04 to 3.33 m(2) m(-3) at 0 degrees and from 0.42 to 2.36 m(2) m(-3) at 30 degrees, and those across all growth stages averaged 1.79 m(2) m(-3) at 0 degrees and 1.52 m(2) m(-3) at 30 degrees. The absolute percent errors of PAI at each growth stage ranged from 1.8% to 66.1% at 0 degrees and from 4.3% to 23.2% at 30 degrees, and those across all growth stages averaged 30.4% at 0 degrees and 14.8% at 30 degrees. The degree of laser beam coverage of the canopy (expressed as index Omega) explained these errors. From the estimates of PAD at 30 degrees, regressions between the areas of stems, leaves, and ears per unit ground area and actual dry weights gave standard errors of 7.9 g m(-2) for ears and 12.2 g m(-2) for stems and leaves. (c) 2012 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS) Published by Elsevier B.V. All rights reserved.