Home
Tutorial Top


Charge distribution 2

Basic equations

There are two basic concepts used to derive equations suitable for describing galvanic surveys.
Additional details needed for developing forward modelling equations are given within the tutorial on general inversion methodology. These details are not needed for a basic understanding of resistivity surveying.

Boundary conditions

When current flows from one material across the interface into a second material, two conditions must hold. Recall that the field vectors describing electric field E and current density J can be decomposed into two components, one that is tangent to a surface and another that is perpendicular, or normal, to the surface. The two boundary conditions are:

Consequenses of Boundary Conditions

There are several important effects that result from these two boundary conditions. Three of relevance to understanding of resistivity are:

.
Charges accumulate in this way at boundaries between regions of differing conductivity. Potentials measured at the surface (the data acquired in a resistivity survey) are a direct consequence of this charge distribution that arises within the ground when current is forced to flow using a high power transmitter. In addition, this concept forms the basis of forward modelling equations which are used to calculate the response to a model of the geology that is composed of a great many small cells, each with it's own, constant conductivity. This is the subject of the forward modelling page in the tutorial on general inversion methodology.

Home | Tutorial Top
EmailWebmaster