Atsushi Rikimaru

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 (pt=1), with vertical distances at the first percentile unaffected by planting geometry. The plant bottom position was identified using three different percentile ranks (pb=95, pb  =80, and pb  =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 pb=95 (r2>0.87; RMSE≈4  cm). Overall, H was typically 16.0 cm greater than   rD with pb=95.

Fundamental study for estimating rice-plant stem number using laser scanner measurements

Abstract. The number of rice-plant stems (S), directly affecting the competition among rice plants and contributing to rice yield, is estimated from laser data. The laser data were normalized to eliminate the increasing plant height effect. Relative spatial volume (rVslaser) was derived and scaled as an exponential function of S. A relationship between rVslaser and S is confirmed in two growing seasons (2014 and 2016, separately obtained by two different laser scanners). The scaling and exponent factors (β and α) depended on the planting geometry, planting density, and bottom position of the rice plants (Dbottom) but were almost independent of the number of divided layers in the rVslaser computation. From the estimated stem number using Dbottom at the 80th percentile (D80), the maximum S was obtained at ∼50 days after transplanting. In both years, the relative error in the estimate was below 0.10, and the bias was small. In the models with D80 in 2014 (MD201480) and D95 in 2016 (MD201695), the β and α values were very similar. Using the rVslaser measure, we can disregard the footprint characteristics and voxel size. The presented results support the proposed approach as a useful future method for estimating rice-plant stems.

Study on effects of unit irradiation area in reflectance characteristics of terrestrial laser scanner

Terrestrial laser scanner(TLS)that have utility in the spatial information acquisition was used in such as three-dimensional measurements of the structure and topography.Reflectance values,which have been recorded together with the three-dimensional information,but it is hardly used for the analysis.TLS Reflection values are affected by several factors. For improvement of TLS data analysis, it is important to elucidate the reflection characteristics of several factors.In this study,it elucidated of the characteristics of the observed object and the unit irradiation,as below.Depending on the occupancy in the unit irradiation area of the objects,the reflectance value is change.