Pak. J. Bot., 37(4): 843-852, 2005. | Back to Contents | ||||
|
Updated: 09-07-09 | ||||
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. |
|||||
Back to Contents |
|
Back to Contents |