DEPTH OF DETECTION OF BURIED CONDUCTIVE TARGETS WITH DIFFERENT ELECTRODE ARRAYS IN RESISTIVITY PROSPECTING

Depth of detection of a target can be defined as that depth below which the target cannot be detected with a given electrode array assuming that the minimum detectable anomaly is 10%. Following this definition, physical modelling was carried out to determine depths of detection of conductive targets of limited lateral extent such as a vertical sheet, a horizontal cylinder and a sphere (infinitely conducting). It is seen that the two-electrode array has the greatest depth of detection followed by the three-electrode array, while a Wenner array has the smallest depth of detection, when the array spread is in-line (i.e. perpendicular to the strike direction). On the other hand, the depth of detection with a Wenner array improves considerably and is almost equal to that of the two-electrode array when the array spread is broadside (i.e. along the strike direction). With an increase in the depth extent of the vertical sheet from 10 to 20 times its thickness, there is an increase in the depth of detection with all arrays except for the three-electrode array when the array spread is in-line, and with the Wenner array when the array spread is broadside.