Application of an estimation model for radiation incidence to the complex terrain of Kuma in Ehime prefecture [Japan]

Evaluation of the intensity of solar radiation on surfaces sloping indifferent directions is important to carry out agricultural operatons over complex terrains. To investigated the distribution of the actual solar energy, a mesh model developed by Kurose was applied to Kuma area, Ehime prefecture in Shikoku, using a grid size of 250m. Emphasis was placed on the performance of the model and characteristics of the spatial distribution of radiational elements. Steps involved in computations of the present model was as follows: (1) collection of basic data of elevation provided by the National Land Numerical Information; (2) calculation of the background of direct beam and diffuse solar radiation on a horizontal surface and a free surface; (3) calculation of the slope inclination, orientation and mean elevation of the surface with a mesh grid of 250m in size as reference; (4) calculation of the shading effect of aerial view factors derived from the relationship between the solar elevation angle and perspective line of the surrounding configuration; (5) evaluation of the spatial distribution of sunshine duration and global radiation fields. Over complex terrains, it was available to estimate the sunshine duration after considering the effects of shading by surroundings. The estimation error was about 0.3 hours in the analyzed area of Kuma. The sunshine duration in the northern surface and area surrounded by steep-slopes was reduced to a minimum. Differences in the sunshine duration over whole meshed areas amounted to about 50 minutes in July and 2 hours in December. A linear relation with a correlation coefficient of 0.991 was observed between the estimated global radiation energy over a horizontal surface and the total solar radiation energy measured with a solarimeter. Estimation error resulted mainly from the interruption by relatively small obstacle at the reference mesh and the value amounted to 8% of the observed value