The geoelectrical resistivity method is performed by injection of electrical curent into the earth through metal electrodes and measure the voltage across two other electrodes. Using one of standard array configurations, the measurements with variable electrode spacings yield apparent resistivity of the sub-surface geological layering.
In 2-D or 3-D resistivity imaging, a large number of electrodes connected to a multi-core cable and an automatic switching system perform measurements that step through programmed combination of electrodes. The ability to redundantly sample very large numbers of electrode combinations results in a detailed resistivity image of the subsurface. Variations in electrical resistivity typically correlate with variations in lithology, water saturation, fluid conductivity, porosity and permeability. Typical modern date geoelectrical resistivity-meter includes the capability to measure the Induced Polarization (IP) as well. IP Parameters such as chargeability or metal factor, are most useful in mineral exploration.