Estimating the leaf inclination angle distribution of the wheat canopy using a portable scanning lidar

The leaf inclination angle distributions of wheat (T. aestivum cv. Norin 61) canopy were estimated at different growth stages (tillering, stem elongation, flowering, and ripening stages) by using a high-resolution portable scanning lidar. The canopy was scanned three-dimensionally by optimally inclined laser beams emitted from several measuring points surrounding the canopy and 3-D point cloud images in each growth stage were obtained. After co-registration of lidar images between different measurement positions, leaves were extracted from the images and each leaf was divided into small pieces along the leaf-length direction. Each of the pieces was approximated as a plane, to which normals were then estimated. The distribution of the leaf inclination angles was derived from the angles of these normals with respect to the zenith. Consequently, distinctive features of the leaf inclination angle distributions at each growth stage clearly emerged. The mean leaf inclination angles on 6 April, 26 April, 16 May, and 5 June were 53.9°, 45.3°, 44.3° and 56.1° respectively and the standard deviations were 19.6°, 22.2°, 21.7° and 19.5° respectively. Moreover, laboratory measurements confirmed that the mean and standard deviations of the absolute error of lidar-derived leaf inclination angles were 4.3° and 2.0°, respectively.