Capacitive Resistivity Imaging with Towed Arrays

Abstract

The capacitive resistivity (CR) technique is a generalization of the conventional DC resistivity method that facilitates measurements of electrical resistivity on engineered surfaces and highly resistive ground. The CR methodology allows the use of towed sensor arrays, thus enabling the rapid collection of high-resolution resistivity data. Under quasi-static conditions CR data are equivalent to galvanic DC measurements so that CR datasets can be interpreted with conventional DC inversion algorithms. In this study, we demonstrate that the methodology and fundamental parameters of the CR technique facilitate spatial sampling at the centimeter scale for towing speeds of the order of 2.5 km/h. We argue that the dipole-dipole array is the most suitable geometry for dynamic CR measurements and present example data acquired with a prototype instrument using plate-wire combinations arranged in an equatorial geometry. The information content of raw CR data is found to be dominant over towing-induced noise and a direct comparison with DC profile data shows good agreement between both techniques. Based on these findings, we show that tomographic imaging is possible using datasets acquired with moving arrays. Closer investigation of the practical aspects of towed-array capacitive resistivity imaging (CRI) highlights the similarities with galvanic multi-electrode surveys, but the different geometric constraints and sampling regime of CRI give rise to advantages (high lateral resolution) as well as disadvantages (limitations in vertical resolution). We conclude our study with recommendations for practical CRI survey procedures and present a field example where we have successfully imaged a subsurface target in 3D. Towed-array CRI is found to provide equivalent (and in some ways superior) information about the shallow subsurface when compared to DC ERT; it therefore widens the scope of electrical 4 imaging surveys to environments where the conventional methodology would be impractical.

Electrostatic multipole for electrical resistivity measurements at the decimetric scale

“…Some authors have referred to this method as 'capacitively coupled resistivity' or 'capacitive resistivity' (Kuras et al, 2006). With multipoles (Panissod et al, 1998;Kuras et al 2007), several pairs of transmitting or voltage poles can be used to sound the material to various depths. If the dimensions of the poles are sufficiently small in comparison with their separation, they can be considered to be point sources for the purposes of model calculations.…”

Current and future role of instrumentation and monitoring in the performance of transport infrastructure slopes

“…Dynamic ground-based sensing systems, such as terrestrial LiDAR (Lato et al 2009(Lato et al , 2012Marjanovic et al 2013;Fan et al 2014), radar inferferometry Caduff et al 2014), ground penetrating radar (GPR; Donohue et al 2011Donohue et al , 2013Silvast et al 2013) and capacitive resistivity imaging (CRI; Kuras et al 2007) can obtain greater spatial and subsurface information, but are limited in terms of temporal resolution by the need for manual data collection, and therefore can be expensive when frequent (i.e. high temporal resolution) monitoring is required.…”

Contribution of 3-D electrical resistivity tomography for landmines detection

“…Therefore, a need has arisen for alternative resistivity imaging methodology like the capacitive electric resistivity system, which does not need direct coupling with the ground surface. The technique is based on a four-point sensors array that is capacitively coupled to the ground and acts as an oscillating non-grounded electric dipole (Kuras et al, 2007). The coupling mechanism between sensors and the ground is then predominantly capacitive and the inductive effects are negligible.…”

“…The entire system is designed to be dragged or towed along the ground surface either manually or mechanically while resistivity can be measured continuously (Milsom, 2003). There are basically, two types of capacitive sensors, one is the capacitive line antennae, and the other is flat plate electrodes (Kuras et al, 2007). Under some conditions, the capacitive measurement of resistivity emulates the DC field surveys and different measurements can be employed with the CR system (such as resistivity sounding, profiling, tomographic imaging).…”