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.