Improved ray-tracing arithmetic of solar radiation model under Larix Dahuric

摘要

A method calculating ray-tracing of solar radiation distribution model under the Larix dahuric was improved to scientifically evaluate and estimate light environment for planting ginseng under forest scientifically. This method considered neighborhood zone of solar radiation, slope angle (α)and aspect (β), which were absent in existent studies. Besides,discussion about relative location between the ray and the canopy was made in more details than other researches. This improvement depended on aspect (β) related three-dimensional and two-dimensional Cartesian coordinate systems, which were established on slope and horizontal respectively. Furthermore, coordinates conversion was achieved by slope angle (α), aspect (β) and the solar elevation angles (θ). Confirmed extension of neighborhood of light protection was a rectangle with 2H（tree height）on the east and west, 0.8H on the south and 0.3H on the north removed from the point where radiation would be calculated. The direct radiation model based on improved arithmetic was also validated under the forests in JingYue Reservoir in Changchun. The regressions analysis between measured and calculated instantaneous values of points and accumulative total value of any point were both made. The regression analysis between measured and calculated instantaneous values of points without sunflecks with 12cm diameter and discriminated trunk-shading by statistics, coefficients of determination R2 were not less than 0.664 (P<0.01), and all percent mean absolute errors (MAE%) were less than 35.8% from May to September, which were more precise than 40% appeared in other researches. Furthermore, R2 between the accumulative total of measured values and calculated was 0.670 (P<0.01), MAE% was 15.5% and root mean square error (RMSE) was 86.7. These results show that improved pathway parameter arithmetic for the model was excellent to estimate direct radiation of most of fixed points in Larix dahuric trees with conical canopies. And it had higher predictions to simulate accumulative solar radiation of any point on soil under the trees during the whole time.