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.
['Yoshikazu Iikura']
Precise Evaluation of Topographic Effects in Satellite Imagery for Illumination Correction