PARAMETER SENSITIVITY MAPS OF SURFACE GEOELECTRIC ARRAYS II. NONLINEAR AND FOCUSSED ARRAYS

In this paper we present, at first time in a geophysical journal, parameter sensitivity maps of nonlinear and focussed electrode arrays. We present them as anomalies due to electric dipoles forming on opposing surfaces of an elementary cube within the subsurface at three different depths, and not only the total effect of the dipole, but also of its components are shown. Parameter sensitivity maps of non-linear arrays, compared to those of linear arrays, have in general 1. more equal sensitivity values in x and y directions, 2. more chances for antisymmetry axes, 3. smoother lateral distribution of sensitivity values. We recommend a systematic use of parameter sensitivity maps in geoelectric prospecting, both in planning and interpretation of field measurements

Classification of Surface Geoelectric Arrays

We have found in the geophysical literature more than ninety different surface geoelectric arrays, fulfilling an updated definition (specifying the current feeding, the potential difference measurement and the geometry of the electrodes). Several composite configurations, with widely varying geometry, have also been collected. We have presented the geoelectric arrays in a systematic way and with a unified notation. The classification is based on three divalent parameters: “superposition” of measurements, “focusing” of currents and “colinearity” of the array, creating 8 groups of geoelectric arrays. For the simplest group (the group of nonfocused, nonsuperposed, colinear arrays) we cover all theoretically possible arrays. For the other groups – due to the infinite variety – we collected only the already existing arrays, but it is easy to create further example arrays. The proposed classification may facilitate a systematic comparison of properties of different arrays and inspire testing new arrays, to find optimal configurations for actual field problems. Finally, the classification certainly helps to avoid rediscovering already published arrays

Auxiliary Results of Collection and Classification of Surface Geoelectric Arrays

Recently, we have made a classification of more than one hundred various surface geoelectric arrays ever published in geophysical literature (Szalai and Szarka 2007a, 2007b). The classification is based on three divalent parameters (as “superposition” of measurements, “focusing” of currents and “colinearity” of the array), thus we set up eight groups of geoelectric arrays. One further group was separated for about 10 socalled “composite” arrays, which cannot be classified in the aforementioned way. Here we present some application examples of the classification results. Namely, we call the attention to some hidden relationships among geoelectric arrays: (1) we give an illustration how various arrays can be derived from their root array (besides the Schlumberger-related arrays several other examples will also be given in the presentation); (2) we provide a summary of arrays, capable to measure various partial derivatives of the electric potential. Among the 21 arrays 14 are already published arrays, but there are seven possible, but not-yet-applied arrays. In this way, such missing links in the genealogic trees may lead to creation of reasonable and purposeful new arrays