Method for estimating rice plant height without ground surface detection using laser scanner measurement

Abstract

A method for estimating the height of rice plants, using three-dimensional laser range data from point clouds, is proposed and assessed. Rice plant height ( H ) is estimated using a reference position at the top of the rice plant, avoiding the need to determine the ground position. Field experiments were performed with a SICK LMS 200 laser scanner in 2013 and 2014 on a test field with five different planting geometries. Percentile analysis identified the closest percentile to the top of the rice plant ( p t =1), with vertical distances at the first percentile unaffected by planting geometry. The plant bottom position was identified using three different percentile ranks ( p b =95, p b =80, and p b =70). Relative vertical distances ( rD ) were computed from the difference between the top and bottom positions of the rice plant. These correlated well with measured H , with slopes greater than 1.0. A greater number of stems in 2014 led to steeper slopes. Estimated H was more accurate when plant bottom positions were closer to the ground surface, and the best results were obtained with p b =95 ( r 2 0.87; RMSE≈4  cm). Overall, H was typically 16.0 cm greater than rD with p b =95.