MULTI-ELECTRODE GEOELECTRICAL PROSPECTIN
Instrumentation for geognostic investigation
This type of survey is based on the calculation of the resistivity from the d.d.p measurements in the ground. The method is based on the introduction of an electric field in the ground through electrodes (input or current) and the measurement of the d.d.p. in other electrodes (of measurement type). From the d.d.p. value, it will be possible to find the resistivity value through the second law of Ohm, which is a typical characteristics of all materials. Since rocks are resistive materials by nature, the resistivity variations are due almost exclusively to the presence of water in different quantities. Electric tomography 2D-3D is carried out by fixing electrode grids in the ground (16, 32, 64, 128….) at constant pitch. All of them are connected to boxes which allow commutation among them, defining which are the measuring and current electrodes from time to time and automatically. The system will automatically perform all possible combinations. For this purpose, a series of measurements will be obtained (as many as the combinations available), based on: the number of electrodes and type of geometric configuration used. The tomographic inversion of the data obtained on the surface generates a bidimensional or tridimensional reconstruction in “output” of the ground, from which it is possible to identify possible anomalies due to cavities, water bodies, etc, and identify shapes, sizes and spatial distribution.