The Evaluation of Various Radiance Components in Mountainous Terrain

There are three basic radiances impinging on a gound target point in mountainous terrain, namely, 1) direct solar radiance, 2) diffusely transmitted radiance, and 3) diffusely reflected radiance by adjacent slopes. These radiances were evaluated quantitatively for various ,sun positions and target slope orientations by using the backward Monte Cdo method. Especially, the evaluation of adjacency effect due to multiple reflections of light by surrounding slopes for realistic topographic conditions was, for the first time, given here. A backward Monte Carlo technique was used to shorten the computer time. We found that the effect of adjacent slope radiance (the adjacency effects) on the observed radiance at satellite level is significant and should not be ignored when the solar elevation angle is less than 40 degrees, whereas it is negligible when that angle is larger than 50 degrees. Both Lambertian reflection model and non-Lambertian model (Minnaert model) were examined in this study.