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

Abstract

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°) and off-vertical (30°). The estimates of PAD and plant area index (PAI) were more accurate at 30° than at 0°. The root-mean-square errors of PAD at each growth stage ranged from 1.04 to 3.33m2m−3 at 0° and from 0.42 to 2.36m2m−3 at 30°, and those across all growth stages averaged 1.79m2m−3 at 0° and 1.52m2m−3 at 30°. The absolute percent errors of PAI at each growth stage ranged from 1.8% to 66.1% at 0° and from 4.3% to 23.2% at 30°, and those across all growth stages averaged 30.4% at 0° and 14.8% at 30°. The degree of laser beam coverage of the canopy (expressed as index Ω) explained these errors. From the estimates of PAD at 30°, regressions between the areas of stems, leaves, and ears per unit ground area and actual dry weights gave standard errors of 7.9gm−2 for ears and 12.2gm−2 for stems and leaves.