APPLICATION OF DIGITAL ENHANCEMENT TECHNIQUES FOR GROUNDWATER EXPLORATION IN A HARD-ROCK TERRAIN

Geomorphological and geological features, namely landforms, rock units and geological structures, have a definite relationship with the occurrence and movement of groundwater in hard-rock crystalline formations. Exploration and exploitation of this sub-surface resource depend upon the understanding of expected subsurface hydrological conditions through surface expressions. The different types of digital enhancement techniques using remotely sensed data help in the extraction of specific features that act as groundwater indicators and ultimately lead to the preparation of maps indicating groundwater prospective zones. In this study, different enhancement techniques, such as linear stretching, band combination, filtering and edge enhancement, have been employed for deriving groundwater-controlling features in typical hard-rock crystalline formations of parts of the Raichur district, Karnataka, India. The qualitative evaluation of each enhanced output for its feature exhibitance has narrowed down the optimum operations to be performed for extracting all the groundwater-related features. The linear-stretched band data and specific false colour composite (FCC) have brought out the details on geology and geomorphology, while the various landforms have been highlighted by the FCC of principal-component analysis. The geological structures have been highlighted by filtering techniques. Band subtraction has brought out the vegetation along valley fills and moisture-laden lineaments. Based on the results achieved, a package has been suggested that can be used on an operational basis for groundwater targeting in typical hard-rock crystalline formations. It should be further used in conjunction with knowledge of local field conditions to aid the investigations made by remote sensing techniques.