A Study on the Radiance Distribution in the Canopy Affected by Non-Lambert Characteristics of Leaf Based on RGM
叶片非朗伯特性影响冠层辐射分布的辐射度模型模拟与分析

As one of the computer simulation models,the Radiosity-Graphics combined Model(RGM) has many advantages in calculating the bidirectional reflectance factor(BRF).Because it takes advantage of radiosity theory and computer graphics technique,the model can contain much more detailed and complex structures of vegetation canopy and take reflection,transmission and multiple scattering into account,which is useful to understand the interaction between the light and the canopy.A hypothesis of Lambertian is made in the general radiosity theory,namely,all surfaces of components(i.e.,leaves,stem and background) in the scene are Lambert reflection/transmission.In fact,studies of the properties of leaves have shown that the bidirectional reflectance distribution functions(BRDF) of most leaves' surfaces are not isotropic.In order to apply RGM to calculate the radiance distribution caused by the non-Lambert(specular) component,a semi-experimental Phong model is used to evaluate the specular radiosity from leaves' surfaces.This method is applied to the maize canopy,and the results are analyzed.As an interesting experiment,this extended RGM,which includes diffuse and specular component at the same time,not only keeps the advantages of the general radiosity theory,but also eliminates the hypothesis of Lambertian in vegetation scene.