EXTRACTION OF SPECTRAL INFORMATION FROM LANDSAT-TM DATA AND MERGER WITH SPOT PANCHROMATIC IMAGERY - A CONTRIBUTION TO THE STUDY OF GEOLOGICAL STRUCTURES

In order to increase spectral contrast from Landsat TM, for geological applications, different procedures of information compression such as colour composite, ratioing, and PCA were tested. Then, to increase th e spatial resolution, a SPOT panchromatic image was combined with the extracted spectral image; merging methods, classic IHS transforms and linear combinations were tested. For these two steps of image processi ng, the best results were obtained by respectively using PCA and a sel ective linear combination. The merging-of the SPOT data was done selec tively in order to avoid the disturbance of the spectral content of th e Landsat TM image. For this reason, only the PC corresponding to the visible part of the spectral domain was combined with the SPOT From th e high spatial resolution and high spectral content final image, a lit hological and structural mapping was produced. This analysis points ou t boundaries between granitic domes and surrounding sedimentary format ions and also highlights the relationships between granitic domes them selves and the fracturing.