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ASSESSMENT OF THE IMAGE VALUE GRADIENT PROBLEM IN THE AMAZON LANDSAT TM DATA

RIFFAT NASEEM MALIK AND SYED ZAHOOR HUSAIN*

Abstract: The main purpose of this study was to investigate the image value gradient problem which was observed in Landsat TM images during the production of WAGIS mosaic (Toivonen et al., 2002) currently present on the Internet-based Western Amazon Geographic Information Service (www.utu.fi/ml/amazon). The results revealed a presence of gradient in image pixel values from west to east direction. The spectral reflectance values in visible bands of the Landsat TM were more affected as compared to the infrared bands. The gradient phenomenon were prominent in land-cover classes where vegetation was a major component (such as forested land), however non-vegetation classes also showed random change in reflectance values along the west to east direction along the gradient. The presence of gradient phenomenon poses serious problem in the use of Landsat TM imagery for image analysis based on reflectance values, change detection studies and the preparation of mosaics using multitemporal Landsat TM imageries. The results further highlight the consideration of gradient phenomenon in developing new image correction methodologies while using the Landsat TM imagery, particularly, in western Amazonian rainforest. These and other related problems are discussed.
 

Department of Biological Sciences, Quaid-e-Azam University, Islamabad, Pakistan.
Environmental Sciences Programme, Fatima Jinnah Women University, The Mall, Rawalpindi, Pakistan.