DEPTH OF DETECTION OF BURIED CONDUCTIVE TARGETS WITH DIFFERENT ELECTRODE ARRAYS IN RESISTIVITY PROSPECTING¹

Abstract

Depth of detection of a target can be defined as that depth below which the target cannot be detected with a given electrode array assuming that the minimum detectable anomaly is 10%. Following this definition, physical modelling was carried out to determine depths of detection of conductive targets of limited lateral extent such as a vertical sheet, a horizontal cylinder and a sphere (infinitely conducting). It is seen that the two‐electrode array has the greatest depth of detection followed by the three‐electrode array, while a Wenner array has the smallest depth of detection, when the array spread is in‐line (i.e. perpendicular to the strike direction). On the other hand, the depth of detection with a Wenner array improves considerably and is almost equal to that of the two‐electrode array when the array spread is broadside (i.e. along the strike direction). With an increase in the depth extent of the vertical sheet from 10 to 20 times its thickness, there is an increase in the depth of detection with all arrays except for the three‐electrode array when the array spread is in‐line, and with the Wenner array when the array spread is broadside.

Resolution, stability and efficiency of resistivity tomography estimated from a generalized inverse approach

“…Numerical perturbation studies examine whether the anomalous response of predefined features in the ground exceed the limits of detectability (van Nostrand 1953; Dey et al 1975; Apparao et al 1992). Both of the above approaches suffer from the disadvantage that they only investigate the influence of a model perturbation on individual or sets of data, but not on the image itself.…”

Anisotropy of electrical conductivity of the excavation damaged zone in the Mont Terri Underground Rock Laboratory

“…A and B represent the electrodes used to inject the electrical current and M and N are the electrodes where the electrical potential Δ V ( A , B , M , N ) is measured (e.g. Apparao et al 1992). Reciprocal measurements corresponding to the sequence { M , A , B , N } have also been made in order to check the reliability of the apparatus.…”

Resistividade e polarização induzida (IP): modelagem analógica

“…Especificamente para resistividade, Apparao et al (1992Apparao et al ( e 1997, em seu estudo de modelagem analógica para modelos condutivos e resistivos (esfera, cilindro e corpo tabular construídos em alumínio e ebonite -um material sintético altamente resistivo) imersos em um tanque comágua, realizaram estudos visando estimar a profundidade limite de detecção destes modelos. Constataram que a profundidade de detecçãoé substancialmente maior quando se trata de um modelo condutivo, principalmente quando se trata dos dispositivos pólo-dipolo e dipolo-dipolo, não sendo tão significativa a alteração para o arranjo Wenner.…”