The geoelectrical and seismic prospecting are the best geophysical surveys known and used for detecting buried structures, locating aquifers, studying pollutants and finding landfills.
This technique consists in measuring the apparent resistivity in different points of the soil, by stringing electrodes. Computer processing of these measures allows viewing the results by explanatory tomographic images.
To measure the resistivity, you enter an electric current in the soil by one or two current electrodes and record the potential difference between two voltage measurement electrodes. The relationship between the voltage and current, multiplied by a correction coefficient that depends on the electrodes geometry, gives the resistivity of the soil between the two voltage electrodes.
There are various geometric positions to place these electrodes (dipole, tripole, Wenner and Schlumberger quadrupole).
It is also possible to have resistivity profiles (Horizontal Electric Soundings): stringing remains in a fixed geometry and completely shifted, along a predetermined path. By operating in this way, it is therefore possible to investigate a constant depth of soil, highlighting any lateral variations in the subsurface.
Otherwise, you can perform the Vertical Electric Sounding: it is kept fixed to the center of the stringing and the distance between the current electrodes is progressively increased, by increasing the investigation depth.
Therefore, it is possible to reconstitute a terrain profile relying on empirical methods, which allow obtaining tomographic sections, as shown in the image below: