The ERT (Electrical resistivity tomography) is a method to map the resistivity of subsoil materials using a DC current injected from a resistivity-meter. The method produces models that reproduce the electrical resistivity in the ground, allowing to derive qualitative information on the type of geologic material and the water content therein. Thus, ETR is a powerful tool for solving engineering and environmental problems.

The ERT works by injecting a continuous current into the soil and measuring the potential difference via a series of electrodes inserted into the ground or in a borehole. Apparent resistivity (defined as the average value of resistivity that a homogenous medium having the same resistance to the passing of current charges would have) is calculated from the injected intensity, the voltage difference created and the geometrical coefficient of the instrument. Collecting automatically a large amount of readings in the field it is possible to invert these datasets to derive a 2D or even a 3D-distribution of resistivities of the subsoil.