1D Resistivity

Method

Transmitter electrodes (A, B) are used to inject current into the ground. The current flow between A and B is measured with the potential electrodes (M, N) (Figure 1).

Figure 1: 4-point-measurement electric flow field Figure 2: 1D Resistivity survey (Stefan and Dominique)

Several 4-point-measurements are taken where the receiver electrodes M, N remain in place and the transmitter electrodes are symmetrically extended outwards. Thus the current penetrates successively deeper into the ground. When the current flow sinks to a layer with different electrical conductivity the current flow field is deformed, this can be measured at the receiver electrodes M, N. From this data a layer model based on the electrical conductivity of the different subsurface materials is calculated.

Figure 3: 1D Resistivity Inversion, Yukon 2007
Instrumentation

The transmitted current is an AC with frequencies of 0.26 to 30 Hz automatically adjusted between 1 µA to 100 mA and up to 400V peak to peak. The voltage measured at the receiver electrodes is amplified by the measuring device. Measuring depth app. 250 ft..

Application

1D Resistivity is a quick method to measure the depth to bedrock, groundwater table, and permafrost at a specific location. 1D Resistivity is however prone to adverse effects due to asymmetrical layers below ground. In these conditions we recommend using 2D Resistivity.