A Modified Geoelectrical Procedure Using Polardipole Arrays—an Example of Application to Deep Exploration *

Abstract

Dipole soundings are more sensitive to noise caused by lateral and superficial inhomogeneities than Schlumberger soundings. However, the former are preferable for deep explorations in view of the relatively short cables required. The simple solution of carrying out the field work by means of dipole spreads, and to transform the dipole resistivity diagrams into Schlumberger ones by means of proper formulae would be valid only for smooth and regular curves; but often, owing to the presence of lateral noises, the dipole data show a considerable scatter. For such cases a “continuous dipole sounding” method is proposed for which all successive dipoles are contiguous, so that all parts of the profiles are covered and interpolation is not necessary. Obviously the moving dipoles have lengths proportional to their distances, so that they appear equal in the usual bilogarithmic scale. It follows that only polar‐dipole arrays may be used. The transition from a dipole to the corresponding Schlumberger apparent resistivity diagram requires an integration constant which is not unequivocally determined. Therefore, the solution is not unique, but all possible derived Schlumberger diagrams have a common part. Similarly, they have some common interpretative results, which may be referred to the original dipole diagram obtained in the field. A special measurement technique is required since the dipole‐dipole voltages to be determined are noticeably smaller than the Schlumberger ones. This is true also because dipole soundings are used for great depths and for long distances between the two dipoles.

Electrical resistivity tomography to investigate geological structures of the earth's upper crust

“…Keller (1966) and Alfano (1974) discussed the advantages of a dipole±dipole con®guration over a Schlumberger con®guration for large electrode layouts. Keller (1966) and Alfano (1974) discussed the advantages of a dipole±dipole con®guration over a Schlumberger con®guration for large electrode layouts.…”

Dipole‐dipole Deep Geoelectric Soundings Over Geological Structures*

“…It is important that (5), (6), and (7) are valid independently of the underground structure. To obtain only one value p,(Xi) and not of a difference implies the knowledge of an integration constant; but this last print has been studied in Alfano (1974). The solution of this problem may be obtained by means of the formula:…”

“…The remaining problem of the evaluation of (27) concern the presence of a sum of infinite terms, namely an infinitely long dipole-dipole field sounding; but, as shown in Alfano (1974) this difficulty may be overcome in practice, and a dipole-dipole sounding of finite length is sufficient. CONCLUSION Dipole-dipole sounding data which are often too scattered to give useful diagrams should be transformed into the more interpretable Schlumberger data.…”

“…Therefore, it makes more evident the average the apparent resistivity diagrams in terms of the deep structures. Some examples on this were discussed in Alfano (1974).…”

A remote-control datalogger for large-scale resistivity surveys and robust processing of its signals using a software lock-in approach

“…In order to achieve deeper signal penetration, one can use dipole-dipole experiments, in which both current injection and voltage measurement are realized by dipoles that are small compared to the total layout (Alfano 1974). Usually, Published by Copernicus Publications on behalf of the European Geosciences Union.…”