Mapping Hydrothermally Altered Rocks and Lineament Analysis Through Digital Enhancement of Aster Data Case Study: Kemashi Area, Western Ethiopia

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Addis Ababa Universty


Hydrothermal alteration, structure and geology of the Kemashi area, western Ethiopia have been studied by means of remote sensing techniques and limited field data. Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) reflectance data have been processed and interpreted with the production of geological map, lineament map and some hydrothermal alteration minerals abundance maps at a scale of 1:125,000. Statistically selected and enhanced 3-bands color composite image of raw ASTER data and images resulted from principal component transformation (PCA) produced substantial spectral contrast between different lithology and enable to interpret the lithological boundaries. Spatial enhancement of ASTER data using convolution filters and digital elevation model (DEM) extracted from the Shuttle Radar Topographic Mission (SRTM) have been used for lineament manual extraction. Hill-shading techniques are applied to SRTM DEMs to enhance terrain perspective views and to extract morphologically defined structures. Foliations, folds, different set of fractures are major structural elements recognized from the image processing and hill-shading techniques. For regional mapping of some hydrothermal alteration minerals “Feature oriented Principal Component Analysis (FPCA)” and band rationing and threshold image processing methods were applied. For both methods application subset of the ASTER bands were selected according to the position of characteristics spectral features of the alteration minerals in the VNIR and SWIR portion of the spectrum. Hydrothermal alteration in the study area mainly consist argillic-altered rocks and iron oxide/hydroxide altered rocks and mapped across various lithologic units. The overall result of this study demonstrates the usefulness of remote sensing method and ASTER multi-spectral data for alteration, structure and lithologic mapping. Keywords: alteration; ASTER; band ratio; digital elevation model; Ethiopia; geology; hydrothermal; Kemashi; lineament; lithology; PCA; SRTM, remote sensing; spectral



Alteration, ASTER, Band ratio, Digital elevation model, Ethiopia, Geology, Hydrothermal, Kemashi, Lineament, Lithology, PCA, SRTM, Remote sensing, Spectral