SHADOWS CORRECTION METHODS FOR LANDSAT SATELLITE IMAGES

This article aims to present the problem about the topographic effects produced by the shadow in the mountain area. The existence of this phenomenon creates confusion between the components of a scene, cause difficulty in establishment with precision the types of land use because the surfaces covered with the same type of vegetation being totally different shown. In this case, even if they represent the same category of use of the land, the pixels found under the shadow have different digital values compared to the sunny ones. Topographic correction, which eliminates the terrain effect caused by the topographic relief, is one of the fundamental steps in data pre-processing. The diminution of the topographic effects can be achieved through various methods which have as result getting clear images by highlighting the information in the shadow. The reflected radiance in topographically complex areas is severely affected by variations in topography; thus, topographic correction is considered a necessary pre-processing step when retrieving biophysical variables from these images. It was assessed the performance of three topographic corrections: Cosine, C-Correction and Minnaert. The performance of topographic corrections on the images was assessed by visual comparison and spectral response analysis. In the majority of cases, C method performed best in terms of eliminating topographic effects comparing with the Cosine and Minnaert methods, which showed the poorest performance.