Optimized survey design for electrical resistivity tomography: combined optimization of measurement configuration and electrode placement

Abstract

Within geoelectrical imaging, the choice of measurement configurations and electrode locations is known to control the image resolution. Previous work has shown that optimized survey designs can provide a model resolution that is superior to standard survey designs. This paper demonstrates a methodology to optimize resolution within a target area, while limiting the number of required electrodes, thereby selecting optimal electrode locations. This is achieved by extending previous work on the 'Compare-R' algorithm, which by calculating updates to the resolution matrix optimizes the model resolution in a target area. Here, an additional weighting factor is introduced that allows to preferentially adding measurement configurations that can be acquired on a given set of electrodes. The performance of the optimization is tested on two synthetic examples and verified with a laboratory study. The effect of the weighting factor is investigated using an acquisition layout comprising a single line of electrodes. The results show that an increasing weight decreases the area of improved resolution, but leads to a smaller number of electrode positions. Imaging results superior to a standard survey design were achieved using 56 % fewer electrodes. The performance was also tested on a 3D acquisition grid, where superior resolution within a target at the base of an embankment was achieved using 22 % fewer electrodes than a comparable standard survey. The effect of the underlying resistivity distribution on the performance of the optimization was investigated and it was shown that even strong resistivity contrasts only have minor impact. The synthetic results were verified in a laboratory tank experiment, where notable image improvements were achieved. This work shows that optimized surveys can be designed that have a resolution superior to standard survey designs, while requiring significantly fewer electrodes. This methodology thereby provides a means for improving the efficiency of geoelectrical imaging.

Uncertainty and Resolution Analysis of 2D and 3D Inversion Models Computed from Geophysical Electromagnetic Data

“…Therefore, it is crucial to select a small set of measurements from all possible measurement configurations which can still optimally resolve the underground structure. Successively augmenting a base set of measurements (Wilkinson et al 2006;Stummer et al 2004;Loke et al 2014;Wagner et al 2015;Uhlemann et al 2018), we can employ the iterative update formulae in Eqs. (50) to (52) to quickly compute the model resolution and covariance matrices of the augmented data set.…”

Three‐Dimensional Time‐Lapse Geoelectrical Monitoring of Water Infiltration in an Experimental Mine Waste Rock Pile

“…Recent developments of the ERT method over the past decade have increased the spatial and temporal resolution for hydrogeological processes monitoring, with optimization of measurement protocols using several hundreds of electrodes (Loke et al, 2014a, 2014b, 2015a, 2015b; Uhlemann et al, 2018; Wilkinson et al, 2012) and with two‐, three‐, and four‐dimensional inversion software (Günther et al, 2006; Johnson et al, 2017, 2010; Rücker et al, 2017, 2006). Moreover, new approaches have been developed to integrate geophysical monitoring results into hydrogeological modeling to complement traditional hydrogeological monitoring techniques for laboratory experiments or field scale studies (Binley et al, 2002; Chou et al, 2016; Dawood et al, 2011; Kemna et al, 2002; Koestel et al, 2008, 2009; Robinson et al, 2009).…”

Feasibility Assessment of Long‐Term Electrical Resistivity Monitoring of a Nitrate Plume

“…While subsurface properties were directly related to conductivity in Archie's law (Equation 4), the ability of ERI to resolve the plume depends heavily on the measurement sequence used to generate the ERI data sets. We used a standard dipole‐dipole sequence, which historically has been shown to resolve features at the electrode spacing and depths used here; however, recent advancements and optimizations on a 3D ERI installation (Uhlemann et al ) have shown promise. Optimization of the survey could provide further refinement of the ERI results in a field installation.…”