Geoelectric imaging properties of traditional arrays and of the optimized Stummer configuration

Abstract

In this paper a systematic, semi-empirical comparison is presented between two-dimensional geoelectric models and their inversion images, obtained by using five different electrical resistivity arrays and an optimized Stummer configuration. Eight different models (more or less in order of growing complexity) are studied and both noise-free and noisy data cases are considered. The results show that (1) the quality of the inversion images obtained with traditional arrays depends significantly on the model and on the noise level, (2) among the traditional arrays it is definitely the dipole-dipole array that provides inversion images mostly similar to the geoelectric models, (3) the inversion images obtained by using the optimized Stummer configuration are even more similar to the original geoelectric model than those obtained by the dipole-dipole array. It means that the optimized Stummer array is even better than the best traditional array, the dipole-dipole array, especially in the deepest part of the inversion images. We conclude that in a general field situation the Stummer configuration is good enough for not being forced to search specific configurations. As presented, optimization procedures, involving null arrays could even further improve the quality of the inversion images obtained by using the Stummer configuration. basis for traditional profiling and sounding techniques they are also important for electrical resistivity tomography (ERT) measurements because the individual arrays serve as a basis for the ERT measurements.ERT measurements, which nowadays play a dominating role in geoelectric probing, should however be handled differently from the individual arrays. In their case the DOI (depth of investigation) introduced by Oldenburg and Li (1999) and the DD (depth of detectability) introduced by values can give information about the depth interval from which one is able to obtain useful information. DOI is the depth, below which any change in the model resistivity has an unobservable effect on the measured signal. The DOI is in theory array-and modeldependent but for the same model, in the case of various arrays, more or less the same DOI value is obtained. At the same time, the DD parameter shows a more significant array-and modeldependence. E.g., the same model by using a given array could be observed from even a four-five times larger depth than by using another array. We supposed a relation between the DD values of the configurations and their imaging properties. The existence of such a relation was verified in this paper.

Multiplication of the depth of detectability using γ11n arrays

“…It is although expected since about the first 600 term of the Stummer array is bipole-bipole type, similarly to the DP-ax array (Stummer et al, 2004). The imaging capacity of the DP-ax and the Stummer arrays is also similar (Szalai et al, 2013). Fig.…”

“…Whilst the configuration is given for only 30 electrodes the electrode distance of the Stummer array was increased to have a section length comparable to the other studied arrays. In spite of a similar modification the Stummer array proved to be the best array in numerical studies (Szalai et al, 2013).…”

“…Motivations to study the γ 11n arrays a) As it has been previously shown the γ 11n ME-arrays provide higher DD-values than other investigated arrays. It may have a great importance also since arrays having higher DD-values seem to have better imaging characteristics (Szalai et al, 2013). b) It has already been demonstrated that null-arrays can be effective and practical for field measurements, too (Falco et al, 2012;Szalai et al, 2002).…”

“…Besides of that DD gives information about the limitations of the given ME array. In the study by Szalai et al, (2013) moreover arrays characterized by the highest DD values have the best imaging features.…”

Electrical Resistivity Imaging and the Saline Water Interface in High-Quality Coastal Aquifers

“…However, acquiring all of these electrode arrangements is prohibitively time-consuming and does not guarantee a superior outcome. Optimized arrays, with trade-offs between acquisition efficiency and optimum ERI resolution, is an active field of research for ERI imaging (e.g., Loke et al 2014aLoke et al , b, 2015bStummer et al 2002;Szalai et al 2013;Wilkinson et al 2012Wilkinson et al , 2006. Several methods of optimization exist; however, the analysis of resolution matrices has proven popular.…”