Methodological Approach in Lithological Discrimination by Digital Processing: A Case Study in the Serra Do Ramalho, State of Bahia

摘要

Problems related to lithologic mapping are discussed. Enhancement techniques and thematic classifications were combined and applied in the lithological discrimination of metasediments of the Bambui Super Group (Upper Proterozoic) in the region of Serra do Ramalho, representative of a widespread transitional environment between semi-arid and temperate conditions, in the southwest portion of the State of Bahia, Brazil. A preliminary methodological sequence is discussed in datail for imagery obtained during the dry season by LANDSAT satellite. Color composites of stretched original data, band ratioing and principal components allow lithological discrimination through grey level and tonal gradations of several metasedimentary sequences, to a degree superior to reconnaissance mapping. Unsupervised (K-Means classifier) and Supervised (Maximum Likelihood classifier) were also applied, and the spatial distribution of the limestone sequence, host to a fluorite mineralization, show satisfactory results for the purposes of this research. However, the effects of vegetation cover and of human activities mask and limit in several ways lithological discrimination in this kind of environment.