A STUDY OF EFFECT OF PLANTING DENSITIES AND DIRECTIONS ON RICE GROWTH MEASUREMENT USING LASER SCANNER

摘要

Laser scanning methods have been proposed to obtain rice growth measurements for high quality rice production. Airborne laser scanners have the capability to observe large areas of rice paddies. However, planting density and planting direction or the moving direction of the rice planting machine general varied among paddy fields, which affects the three dimensional (3D) point-clouds of rice plants obtained with a laser scanner. In this study, the effect of planting densities and directions on rice growth measurement by using a laser scanner was examined on the basis of field observation data. Test field was divided into five plots with sparse, moderate, and dense planting densities of 11.2 plants/m~2, 15.1 plants/m~2 and 21.2 plants/m~2 respectively and two planting directions parallel and perpendicular to scanning plane. The laser scanner was mounted on rack at height of 3 m to observe rice canopies in the nadir direction. Plant height, number of stems and vegetation coverage were measured manually. The rice growth indices were computed as the product of plant height and number of stems. The percentile heights at special percentile ranks were calculated to compare the vertical distance profiles among test plots. A comparison between the 99th percentile values (H_(99)) and plant height revealed a high correlation despite the various planting densities and directions. H_(99) corresponded to plant height in 60-85% of the cases. Moreover, the percentile heights corresponding to the top layers of the plants at H_(75), H_(95) and H_(99) related to rice growth index did not differ significantly between the plots when the vegetation coverage was less than 50%. Thus, the effect of planting densities and directions on rice growth monitoring by using a laser scanner was negligible within the early study period.