Geo-electric research

The geo-electric method records the differences in the specific electric resistance in the subsurface with the aid of a battery, two electric current electrodes and two potential electrodes. First of all, an electric current is introduced into the ground, after which the potential difference is measured across two potential electrodes. This potential difference together with the strength of the electric current generates a constant that is independent of the measurement set-up used, revealing on the basis of Ohm’s Law the apparent resistance of the subsurface.

There are many different kinds of geo-electric measurement. The DINO database contains data from two types:

  • Vertical Electric Sounding (VES) measurements are performed along a horizontal line from the surface and generate a 1D model in the centre of the measurement set-up.
  • Continuous VES (CVES) is also performed along a line, and generates a 2D profile of the subsurface

The measured apparent resistances are averages of the uppermost layer of the subsurface. A VES measurement has a fixed central point. During the VES the outermost electric current electrodes become increasingly separated – the further apart they are, the deeper we can “see” into the ground. And the deeper we go into the subsurface, the less detail can be observed by this method.

The results of the measurements are translated by computer programs into a strata model of the subsurface. The strata model yielded by a VES comprises the depths (d) and specific electric resistances (Rs) of the distinct layers. The specific electric resistance provides information about the lithology (clay, sand and gravel) of the layer and the salinity of the groundwater.

The most common applications of the interpreted VES measurements are:

  • to determine the depth of the fresh/salt groundwater divide;
  • to create geological and hydrological profiles in combination with drilling data;
  • to determine the electric resistance of the subsurface (for example, for the introduction of cathodic protection)

Geo-electric research on the map

Geo-electric research can be found on the map under Subsurface research. Information on subsurface resistivities can also be found under Geological borehole research, where SN, LN, (Elektrical) Resistance and Induction gives information on subsurface resistivities.