Introduction
Observation of electric fields caused by current introduced into the ground as a means of studying earth resistivity in geophysical exploration. Resistivity is the property of a material that resists the flow of electrical current. A resistivity survey is an example of active geophysical method because this method requirements the injection of an electric current into the ground through electrodes and it measures the resistivity (response) of the ground in the subsurface. Resistivity thus differs fundamentally from the electromagnetic methods such as EM-34 which do not require ground contact. A resistivity survey can produce detailed pseudosection of the subsurface which can be used as a measure of the depth to the apparent resistivity. It is often used in combination with EM surveys to provide more detailed subsurface information.
Operation
Data is acquired using an arrangement of four electrodes known as arrays. The most common used arrays are the Wenner, Schlumberger and dipole-dipole for ground water investigations. Data can be acquired in a sounding or profiling mode, or both simultaneously. In profiling, the lateral variation of resistivity is studied by keeping the depth constant. In profiling, different depths are investigated at the same position. Lateral resolution is limited by the spacing of the voltage electrodes and current electrodes. Vertical resolution depends on the conducting environment but as a rule of thumb it is difficult to resolve a layer that is thinner than the depth to its upper surface. Depth is determined by electrode spacing.
Applications
- Pollution plume mapping
- Mapping bedrock topography
- Landfill and waste dump investigations
- Mapping subsurface voids
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 Example of a 3D fence diagram of resistivity sections |
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