Principles

The objective of electrical tomography is to determine the real resistivity of subsurface materials by measuring potential differences via the continuous injection of an electrical current in the ground.

The principle of a resistivity measurements

The Resistivity R of a media is the measure of the media's ability to oppose electric current. The unit of resistivity is the ohm per meter (Ω·m).

Using  Ohm's law ( R = ∆V / I ), the resistance of the media can be calculated.

ρapp = k ∆V / I

Then, using the geometrical factor K which depends on the electrode configuration, apparent resistivity can be calculated.

The measured data gives apparent resistivity. Using mathematical inversion, the distribution of true resistivities in function of the depth can be found.

The geo-electrical images thus obtained give pseudo-sections which, when correlated with other information (such as borehole data, in-situ measurements, and piezometric data); allow the geological structure to be derived.

  • Investigation depth depends on the electrode spacing
  • As with all geophysical methods, there is an anti-correlation depth of investigation/ resolution
  • Maximum depth of investigation is 100 meters, resolution +/- 10 meters