Electrical Sounding with Capacitive Potential Electrodes - A New Measurement Technique

We present a new electrical array designed for vertical electrical sounding (VES) with capacitive potential electrodes and grounded current electrodes. Two grounded current electrodes are at a permanent position, and two moving equal ungrounded lines are used to measure the voltage. The potential lines are moved away from the current electrodes to increase the depth of investigation. The length of the potential lines is simultaneously increased to keep the geometrical factor small enough, which allowed obtaining a reasonable signal to noise ratio. We tested the proposed array in the field conditions. One current electrode was settled at the beginning of the sounding line, and another electrode was placed 180 m far away. The offset between the nearest current electrode and the center of the potential line varied between 10 and 80 m. The current frequency was 625 Hz. We used an equivalent conventional grounded array (4.88 Hz) as the reference. We found a strong correlation between the voltages obtained with the two arrays. However the voltage and, so, the apparent resistivity obtained with the capacitive electrodes were found to be overestimated. We propose an empirical approach to reduce data obtained with the proposed technique to the conventional VES.