Modeling the Effects of Various Radiant Transfers in Mountainous Terrain on Sensor Response

In mountainous terrain, variations in remotely sensed spectral data caused by variations of slope orientation with respect to sources of incident radiation need to be considered before accurate classification of multispectral data can be achieved. A model was developed to study a number of problems relevant to remote sensing in mountainous terrain. The model is capable of simulating the effects of anisotropic sources of irradiance (direct solar, sky, and adjacent slope fluxes) and bidirectional reflectance properties of the target surface on sensor response for various slope orientations. The model was described and utilized to explore the errors associated with two practical techniques for accounting for the topographic effect on sensor response. Technique #1 was a simple cosine correction of the direct solar source, while technique #2 considered both the direct solar and the diffuse sky sources. For the specific anisotropic irradiance conditions and Lambertian scenes of this study relatively significant errors (> 11-percent error in reflectance) of technique #1 occurred at all wavelengths with slope inclinations greater than 20°. This error was diminished by greater than 50 percent when technique #2 was used. With the recent development of methods for integrating digital terrain data with remote sensing data it has become possible to apply such techniques.