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Geophysical Studies
Integration and Standardization
Geophysical methods and techniques are based on measuring certain physical properties of the subsurface, which are translated into hydrogeological conditions. They are not all equally responsive to the hydrogeological conditions and have their inherent limitations and ambiguities. Therefore, a combination of methods and techniques is preferred. It is then critical to integrate and standardize the results obtained through the different geophysical methods to arrive at the least ambiguous positive anomaly.
For example, the Deccan Trap flow sequence represents stacked layers of varied thickness and high and low resistivity. Once a thick high resistivity layer representing massive basalt is encountered, the vesicular basalt layer underlying it cannot be unambiguously detected by resistivity sounding alone and an attempt has to be made through a combination of other geophysical techniques. Using appropriate integration of field techniques and joint interpretational procedures, deeper aquifers occurring in such a complex geological environment can be delineated. One other area of constraint and ambiguity is the delineation of deeper thin saturated fracture zones in granites and gneisses where again the electrical resistivity sounding and profiling alone may not be always successful. Equally difficult is the delineation of deeper fresh water aquifers underlying a thick saline water zone in coastal areas. The pilot areas having all such hydrogeological problems are thus studied through a combination of multiple geophysical techniques and integrated interpretation and standardization of the data.
The process starts with joint inversion of Vertical Electrical Sounding (VES), Electrical Resistivity Imaging, and Time Domain Electromagnetic (TEM) Sounding data. This reduces the ambiguity in interpretations. These ground geophysical survey data are then integrated with the Heliborne survey data.
Following this, the geophysical parameters are standardized through lithological and geophysical logs of boreholes drilled at selected sites.