REMOTE SENSING AND CAST SHADOWS IN MOUNTAINOUS TERRAIN

In mountainous environments with high relief, topographymay cause cast shadows due to the blocking of direct solar mdiation. Optical-injinred remote sensing images of these landscapes display reduced values of reflectance for shadowed areas compared to non-shadowed areas with similar surjace cover characteristics. Different approaches to dealing with cast shadows are possible, although a common step in various active approaches is first to delineate the shadows using an automated algorithm and a digital elevation model. This article demonstmtes a common confusion caused by cast shadows and describes a quantitative spatial evaluation of a cast shadow delineation algorithm in comparison to human interpretation of a Landsat TM image. It is shown that 86 percent of cast-shadow pixels were correctly marked by the algorithm. The causes of differences between the algorithm and human interpretation are discussed, and alternatives are considered for dealing with cast shadows in classification studies using optical-infrared images of mountainous terrain.