Precise Evaluation of Topographic Effects in Satellite Imagery for Illumination Correction

Radiation field reaching a slope surface was modeled with three additive terms: the direct solar irradiance, diffuse sky irradiance E_d, and reflected irradiance from adjacent terrain E_t. Most methods of topographic effect correction of satellite imagery, however, did not treat E_d and E_t properly because exact calculation would require huge computation power. In this paper, we use fast algorithms for generating horizon and viewshed to evaluate E_d and E_t, respectively. To demonstrate the difference between approximate methods and the exact method, we use an actual Landsat TM image and evaluate the E_d and E_t of every pixel in the image for most bands.