SHOTA GOYA

Fundamental Study on Rice Plant Height Estimation in Wide Areas by UAV-LiDAR Measurements

KAZUYOSHI TAKAHASHI

Plant height, one of the fundamental crop growth parameters, is usually collected by a direct measurement. Phan et al. have developed a method for the estimation of rice plant height by using a short-range LiDAR measurement from above a paddy rice canopy. Phan et al. showed that plant height can be estimated with estimated error (RMSE) of 4 to 10 cm in terrestrial LiDAR experiments targeting paddy rice until heading time. In their method, the estimated rice plant height is calculated based on the analysis of the vertical distribution of 3D point cloud data, therefore the estimation is affected by foliage abundance, laser incident angle conditions and laser footprint size. 
In this paper, for rice plant height estimation in wide areas, I measurement rice growth periods of 2017 and 2018 from 1 month after transplant to heading stage using a short-range LiDAR. Then, I examined effect by foliage abundance, laser incident angle conditions and laser footprint size of rice plant height estimation.
Based on analysis of examination data, the following results have been obtained;
1) The influence of the incident angle condition was similar in different foliage abundance until the maximum tiller number stage in plants with similar height but different foliage abundance. In addition, the estimation of rice plant height was not affected by foliage abundance in a laser incident angle less than 8 degrees which is almost a vertical incident condition.
2) The influence of the laser footprint size could not be confirmed of LiDAR measurement same area at different altitude.
3) Plant height estimation was impossible in the actual field. The cause may be the influence of weeds in paddy rice cultivation method and rice community.
From the above 1), even if the measured altitude is changed, if the footprint diameter is the same, there is a possibility that the plant height estimation method can be applied by limiting to the vertical incidence area.