ERSC 3V93 Lecture Notes - Lecture 38: Refraction, Depth Sounding
3 May 2016
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Measure potentials using second set of closely spaced electrodes placed between current electrodes distances between electrodes are r1, r2, r3, r4. As voltage electrodes are moved closer to either current electrode we would see an increase in voltage. At position close to current electrode we would actually be measuring contact resistance of probe and not ground. In practice we keep voltage electrodes at a minimum distance from i electrodes. Current is refracted at boundaries with contrasting according to a tangent law of refraction same refraction law applies to groundwater flow across boundaries. For increasing resistivity across boundary, current flow lines bend down, towards higher resistivity layer shortest path through high resistivity layer. For decrease in resistivity across boundary, current flow lines bend up towards upper layer. By increasing the current electrode spacing (leaving v electrodes at same position) we can measure the resistivity of consecutively deeper layers basis of resistivity depth sounding.
