User:Gralex

Vertical Electrical Sounding

Vertical Electrical Sounding (VES) ist the method for an investigation of the geological medium. The method is based on the estimation of the electrical conductivity or resistivity of geological medium. The estimation performed based on the measurement of voltage of electrical field induced by the distant grounded electrodes (current electrodes). The Figures 1.-4. show the possible configuration of the measurement setup. Electrodes A and B are current electrodes which are connected to a current source, N and M are potential electrodes which are used for the potential measurements. As source the direct current or low frequency alternating current is used.

Figure 1. Electrical profiling using four-electrode probes in Wenner configuration.

Figure 2. Electrical profiling using four-electrode probes in Schlumberger configuration.

Figure 3. Three-electrode array profiling.

Figure 4. Dipole-dipole electrode array profiling.

The interpratation of the measurements can be performed based on the apparent resistivity values. The depth of investigation depends on the distance between the current electrodes. In oder to obtain the apparent resistivity as the function of depth, for each position the measurements are performed with several different distances between current electrodes.

$\rho _{k}=k{\frac {U_{MN}}{I_{AB}}}$

here, k geometric factor, ${U_{MN}}$ — voltage between electrodes М and N, ${I_{AB}}$ — current in the line AB. The geometric factor is defined by

$k={\frac {2\pi }{{\frac {1}{r_{AM}}}-{\frac {1}{r_{BM}}}-{\frac {1}{r_{AN}}}+{\frac {1}{r_{BN}}}}}$

here r — distance between electrodes.

Interpretation of gathered data is performed based on the dependency ρ_k(AB/2).

For more advanced interpretation the techniques based on numerical methods can be applied.

Freeware for numerical calculations

• Solution of inverse problem
• Solution of forward problem

See also

• Magnetotellurics
• Telluric current
• Seismo-electromagnetics
• Electrical resistivity tomography