ABSTRACT
An electromagnetic induction (EMI) measurement manifests a response to all variations in electrical conductivity that occur within a skin depth dependent volume. EMI imaging is an emerging technique for which relatively little is known and no commercial implementing software is available. This is not the case for a conceptually similar imaging procedure known as electrical resistivity tomography (ERT). The ERT imaging concept, as presented here, will be based on the changes in the flow of electricity in the underground that result from the presence of buried objects. The chapter presents that the final element of the resistivity measurement process where voltage measurements are made on the ground surface. Since the electrical resistivity of water is considerably lower than that of dry soil or rock, geometric depth sounding is commonly used in groundwater resource exploration. A corresponding estimate of object depth by geometric depth sounding is more problematic and imprecise.
