Anomaly effects of orthogonal paired-arrays for 3D geoelectrical resistivity imaging

Abstract

A series of 2D apparent resistivity data were generated over two synthetic models representing different geological or environmental conditions commonly associated with geophysical applications for hydrogeological, environmental and engineering investigations. The apparent resistivity data were generated for the following arrays: Wenner-alpha (WA), Wenner-beta (WB), WennerSchlumberger (WSC), dipole-dipole (DDP), pole-dipole (PDP) and pole-pole (PP) arrays, which were paired such that apparent resistivity data for 2D profiles in a parallel direction are obtained with a particular array type and those in a perpendicular direction are observed with a different array type. The 2D apparent resistivity data for the orthogonal paired-arrays were then collated to 3D data sets. The effectiveness and efficiency of the orthogonal pairedarrays in 3D geoelectrical resistivity imaging were evaluated by determining the mean absolute anomaly effects of the electrode configurations on the synthetic models. The results show that DDP-PDP, DDP-PP, DDP-WSC, PDP-PP, DDP-WB, PDP-WB and WB-WSC orthogonal paired-arrays produced higher anomaly effects on the synthetic models. This indicates that DDP-PDP, DDP-PP, DDP-WSC, PDP-PP, DDP-WB, PDP-WB and WB-WSC orthogonal paired-arrays are more sensitive to 3D features of the geologic models than the other orthogonal pairedarrays investigated.

Analysis of the Influence of the GPS Errors Occurred While Collecting Electrode Coordinates on the Electrical Resistivity of Tumuli

“…Three radials [18,22] 2D-ERTs (T2-T4 in Figure 1) with a theoretical inter electrode distance equal to 1.0 m (linear length 71.0 m) and with DD and PD configuration were acquired. Given the spatial distribution of these ERT, and also according to the recent literature about radial ERTs on tumuli [18,22], C-or O-shaped 3D-ERTs on funeral mounds [17], and imaging resolution of 3D-ERT [26], it is obvious that more ERTs are necessary to cover the whole tumulus and better reconstruct the subsurface anomalies. Therefore, as mentioned also in the introduction, the results of C1, T2-T4 will not presented and discussed in this paper, while it is possible to find a brief presentation of the first results in Pazzi et al [40].…”

“…In the ERT field, the anomaly effect (AE) has been introduced, since the end of the '70s, to estimate the array effectiveness and imaging capability [7,26,27,29]. This parameter is a measure of the signal to noise ratio (SNR), because the signal has to be appreciably greater than the background noise [26]. Given an electrode configuration, the AE value depends on the electrical anisotropy subsoil distribution.…”

“…The second kind of error is caused by a wrong positioning of the electrodes and/or by ignoring the topography in the inversion procedure [23][24][25][26][27][28][29][30]. In particular, a wrong electrode positioning can occur: (a) when electrodes are set up by means of a tape or a string (and therefore a human error can occur), (b) when the interelectrode distance is equal to the cable fixed-space between two connections, but the cable could not be properly stretched because of the topography conditions and the terrain roughness, (c) when some electrodes have to be moved from their theoretical position to be better coupled with the soil (because of the topography and/or the presence of rocks), and d) when the finite cable length does not allow one to place the remote pole/s at the theoretical infinite distance (according to the chosen array).…”

“…Then, the dipole-dipole (DD) array is the most sensitive to mispositioning errors [14,25] because the changes of its geometric factor are proportional to the cube of the distance between current and potential dipoles. In a pole-dipole (PD) array, electrode-spacing errors can also be caused by the position of the remote pole, that is commonly assumed to be located at an infinite distance from the ERT line [26,27,29,30]. Razafindratsima and Lataste [29] discussed the results of inverted models and field surveys performed to evaluate the errors in apparent resistivity and geometric factor using both the infinite theoretical distance and the finite real position of a remote electrode.…”

Identification of 3d Leachate Distribution in Semarang State University Landfill

“…Daerah dengan nilai resistivitas rendah terdapat pada lapisan tanah dengan struktur batuan lempung yang tercemar air lindi. hasil dari penggambaran 3D adalah grid persegi atau grid persegi panjang dengan spasi elektroda konstan dalam arah sumbu x, y, dan z [10]…”