ELECTRICAL RESISTIVITY TOMOGRAPHY IN CONTINUOUS CURRENT (ERT 2D): Although it started from the basic principles of geoelectrics, electrical tomography (ERT) has opened a new chapter in the history of geophysical surveys: in this case, the survey on the ground is carried out in an automated way using a multi-electrode cable with stakes distributed along a profile at a distance of a few meters. The measurements obtained by applying a direct current to two stakes inserted in the ground (current electrodes A B or C1 C2) and measuring the corresponding voltage between two others (voltage electrodes M N or P1 P2) proceed automatically according to the desired sequence, returning apparent resistivity values at different depths and locations along the profile itself. The final result of the processing of this data is a two-dimensional profile of the distribution of soil resistivity values. By combining several parallel terrain resistivity profiles, a high-resolution 2.5D image can be obtained.

ELECTRICAL RESISTIVITY TOMOGRAPHY IN ALTERNATE CURRENT: At its debut, electric tomography (ERT) for geology has always been substantially based on the original principles of Vertical Electrical Surveys (SEV): apply a continuous current to two stakes inserted in the ground (current electrodes AB or C1 C2) and measure the corresponding voltage between two other (M N or P1 P2 voltage electrodes). By conducting an investigation on the ground with a multielectrode cable and performing a sequence of measurements automatically, the current applied and then the relative voltage in general are continuous, with polarity reversal for each measure. Unlike this, the innovative POLARES32 uses a sinusoidal alternating current with an adjustable frequency, allowing measurements to be made more quickly, but keeping the same high quality of the results. This increased speed means a reduction in the time needed to perform a series of field measurements by a factor of at least 10 (or 20 in most cases) compared to the traditional DC system. Moreover, the measurement of the relationship between the voltage detected and the injected current, in sinusoidal state, both as amplitude and as phase (delay of one signal on the other) allows - with a single measure - the simultaneous detection of resistivity and induced polarization of the ground.