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Geoelectrical surveys
The measurement of electrical resistivity of the subsurface is one of the oldest geophysical methods (VES). It was developed during the late 1980s and the early 1990s as an electrical 2D and 3D imaging method for mapping the resistivity distribution in the subsurface CVES/ERT. Electrical resistivity is effective for shallow subsurface mapping at a good resolution. Its clear advantage is in its indifference to electromagnetic noise produced in the urban environment.
Vertical Electrical Sounding (VES) developed at the beginning of the 20th century owing to the work carried out by the Schlumberger brothers, who examined the vertical distribution of the electrical resistivity of the subsurface. A direct current (DC) penetrates the ground through a pair of current electrodes – AB, and the difference in the potential created in the ground is measured between two potential electrodes – MN. There are various deployment patterns for the electrodes (Fig. 1), each of which may be used to examine the distribution of electrical resistivity in the subsurface as a function of depth or of their lateral array. Sounding is carried out by increasing the spaces between the electrodes in a systematic manner, in reference to a predetermined central point. A vertical profile is used to measure lateral changes, where the spaces remain constant as the entire array is moved along a certain line in the field.
- Environmental applications: detecting, locating and mapping the movement of contaminated fluids and pollutants in the subsurface that originate in leaking gasoline tanks and in waste disposal landfill sites, and locating and mapping the intrusion of saline water into groundwater.
- Civil engineering: locating and mapping voids and caves
- Geology: mapping shallow geological formations