Extending RGM to simulate the directional reflectance for complex mountainous regions

As one of the computer simulation models, RGM (Radiosity-Graphics combined Model) can take the processes of reflectance, transmittance and multiple scattering among and between canopies into account. It is appropriate for simulating the directional reflectance from some small canopies and the simulating results are validated well, but the model is difficult to simulate the reflectance of complex scenes, such as mountainous region because the algorithm of RGM is complicated and time-consuming. In order to research the characteristics of the radiation and the reflectance from complex mountainous region, RGM is extended to simulate the directional reflectance from all kinds of topography in this article. To conquer the two disadvantages in RGM, the model is modified in two steps. Firstly, complex mountainous scenes are simplified to only keep DEM. Secondly the algorithm of Radiosity is modified to couple other BRDF (Bidirectional Reflectance Distribution Function) models of vegetation, such as NADIM model, to consider directional radiation of the surfaces of DEM (Digital Elevation Model). A DEM scene produced by a normal distribution random number and a real DEM scene from Tibet Plateau are used to test the modified RGM and the results are analyzed simply.