Abstract
The leaf inclination angle is a fundamental variable for determining the plant profile. In this study, the leaf inclination angle was estimated automatically from voxel-based three-dimensional (3D) images obtained from lidar (light detection and ranging). The distribution of the leaf inclination angle within a tree was then calculated. The 3D images were first converted into voxel coordinates. Then, a plane was fitted to some voxels surrounding the point (voxel) of interest. The inclination angle and azimuth angle were obtained from the normal. The measured leaf inclination angle and its actual value were correlated and indicated a high correlation (R2 = 0.95). The absolute error of the leaf inclination angle estimation was 2.5°. Furthermore, the leaf inclination angle can be estimated even when the distance between the lidar and leaves is about 20 m. This suggests that the inclination angle estimation of leaves in a top part is reliable. Then, the leaf inclination angle distribution within a tree was calculated. The difference in the leaf inclination angle distribution between different parts within a tree was observed, and a detailed tree structural analysis was conducted. We found that this method enables accurate and efficient leaf inclination angle distribution.
Highlights
The leaf inclination angle is one of the most important plant structural parameters
It was reported that leaf inclination angle distribution should be characterized first to evaluate the leaf area index [5]
The leaf inclination angle distribution is a fundamental variable for determining the plant profile
Summary
The leaf inclination angle is one of the most important plant structural parameters. It determines the radiation transmission within vegetation canopies [1], relates to light distribution within a canopy, affects the photosynthetic productivity of the entire plant [2,3], and helps to calculate the flux densities of radiation on leaf surfaces [4]. Some previous studies on leaf inclination angle estimation with 3D images are available [32,33,34,35,36,37] In these studies, the points that composed each leaf were fitted to a plane by a least-squares method, and normals to the planes were calculated. Owing to the manual operation, the number of leaves that can be examined is limited To overcome this problem, a previous study [38] converted 3D point cloud images obtained with structure from a motion method into a voxel-based 3D image. The described method was applied to 3D images of trees obtained from lidar, and the leaf inclination angle at each small point was estimated accurately. The leaf inclination angle distribution within a tree was explored
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