Extraction of spectral information from Landsat TM data and merger with SPOT panchromatic imagery — a contribution to the study of geological structures

Abstract 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 the 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 processing, the best results were obtained by respectively using PCA and a selective linear combination. The merging of the SPOT data was done selectively in order to avoid the disturbance of the spectral content of the Landsat TM image. For this reason, only the PC corresponding to the visible part of the spectral domain was combined with the SPOT. From the high spatial resolution and high spectral content final image, a lithological and structural mapping was produced. This analysis points out boundaries between granitic domes and surrounding sedimentary formations and also highlights the relationships between granitic domes themselves and the fracturing.