To estimate spatial distribution of direct and diffuse radiation, an attempt was made to describe the soybean canopy architecture by eleven parameters. The morphological measurement were pursued periodically throughout the growing season from July to October. These prototype soybean models constructed in the computer were arranged as the planting pattern in the field. A rectangular net of mesh size 10 cm×10 cm was constructed over an unit region (80 cm×30 cm) between the rows as shown in Fig. 11, and the view factors from each of the nodes to the sky were calculated using hemispherical figures as shown in Fig. 12, 13. Spatial distribution of shortwave radiation of each stages was calculated. The calculated shortwave radiation at the ground level agreed well with the measurement by tubetype solalimeters distributed on the soil surface as shown in Fig. 14, 15, 16, 17, 18. This procedure can easily be expanded to estimate radiational environment of any crops, plant densities and growing stages.
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