The Wenner-Schlumberger array

In areas with limited open space for a long, short survey line, the conventional WENNER-SCHLUMBERGER array has a disadvantage in that there is a large reduction in horizontal coverage when the electrode spacing is increased in order to achieve a deeper depth of investigation.

For example, in order to increase the depth of investigation by two times, the electrode spacing has to be increased to 2a the total length of the array is increased from 3a to 6a. At the same time, the width of the pseudo section decreases by 3a with level of measurement.

The steps used by the (a) WENNER and the (b) WENNER-SCHLUMBERGER arrays to increase the depth investigation.

Where R is the measured resistance, it is the spacing between the P1 and P2 electrodes and is the ration of the distances between the C1-P1 and the P1-P2 electrodes.