MERGING SEASAT AND SPOT IMAGERY FOR THE STUDY OF GEOLOGICAL STRUCTURES IN A TEMPERATE AGRICULTURAL REGION

This study highlights advantages of using radar data combined with multispectral data to improve the interpretation of the geology over temperate agricultural regions. After speckle reduction and geometric correction, a Seasat image was combined with a multispectral SPOT image in order to enhance geological features. Two different merging procedures have been examined: photographic and numerical procedures. The photographic techniques consist in assigning the cyan, magenta, and yellow gun colors to the Seasat and SPOT channels. Combinations such as XS2-Seasat-XS3 or XS2-XS3-Seasat improve enhancement of the hydrological network and of the agricultural parcels, both features depending on the basement structure. The numerical procedures include principal components analysis (PCA) and IHS transforms. The PCA appears to be the best numerical procedure to merge Seasat and SPOT data, if centered and standardized data are used as input files. When using the IHS merging procedure, the best results were obtained after a weighting of Seasat by the XS3 SPOT channel. However, results obtained when using IHS transform show less enhancement than when using PCA. Lineament maps were derived from the merged color composites. The geometry of the south armorican shear zone is defined. This geometry corresponds to kilometric C surfaces and S planes. The merging of Seasat and SPOT also points out circular features which correspond to known or previously unmapped granites.