V.E.S. (Vertical Electric Survey) geoelectric prospection method consists in investigating the resistivity variation of a specific territory with depth. It belongs to the most ancient indirect geognostic surveys, non-invasive, which allows to analyze long soil profiles at great depth, with low costs and without disturbing existing buildings or underground water flowing. V.E.S. (Vertical Electric Survey) technique includes a series of resistivity determinations performed by increasing distance between current electrodes (A-B) and potential electrodes (M-N), according to the array of 4 electrodes outlined as it follows. A continuous current is input into the ground throught two external electrodes A and B supplyed by dry batteries or a generator; through central electrodes M and N a potential difference is generated into the ground while the current that flows between A and B is measured. Potential difference measures (pd) and current intensity (I) are measured with precision instruments, equipped with spontaneous potentials.
Electrodes must be along a linear direction, preferibly with minimum slopes to reduce errors caused by rough topography. Generally speaking current density increases in dumps and decreas in correspondence of hills. For quadrupole measures it is recommended to plan array in order to easily position cables while proceeding with measurements. In particular if a user wants to perform survey with arrays of hundreds of meter in length. Resistivity diagrams represent tool resistivity -depth based on subsoil lithologic situation. In quantitative interpretation, inverse process must be done to detect soil model in terms of thickness and layers resistivity according to resistivity trend with depth. This procedure is made through a computing program that applies a proper mathematics model.
The basic components of any acquisition system are: transmitter or current source; receiver which measures the resulting electrode potentials; multiplexer to connect quickly and automatically the electrodes to the transmitter and receiver; a computer for system control and data archival.
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