Fundamentals of the capacitive resistivity technique

Kuras, O.; Beamish, David; Meldrum, Philip; Ogilvy, R.D.

doi:10.1190/1.2194892

Cited by 116 publications

(135 citation statements)

References 21 publications

(29 reference statements)

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“…The application to archaeological studies of such an capacitively coupled approach and its equivalence to ERI are shown in Tabbagh et al (1993); the underlying theory of this equivalence is reviewed in Kuras et al (2006). However, both studies are based on a quasi-static approach employing point poles instead of sensors with finite dimensions.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Capacitively Coupled Resistivity Imaging Measurements on Rock Samples

Uhlemann¹,

Kuras²,

Green³

2012

Proceedings

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SUMMARYEstimation of electrical properties in permafrost studies can benefit from capacitive resistivity imaging (CRI), which overcomes the limitations of usual electrical resistivity imaging employing galvanic coupled electrodes. However, the response of these systems is not fully understood yet. We have used numerical finite element modelling to investigate the complex transfer impedance as measured by a quadrupole consisting of sensors with finite dimensions. Next to a parameter study over a homogeneous halfspace, also an actual experimental setup is modelled. The numerical results are compared to a quasi-static approximation based on point-poles and measured data, respectively. The parameter study shows that the real part of the complex transfer impedance can be approximated by the quasi-static approach in case the dipole separation is large compared to the sensor dimensions. It is shown that quantification of the imaginary part is difficult and depends strongly on the geometric setup. The results of the simulation of a 3D finite rock sample indicate that finite element modelling can be a practical tool for improving the understanding of the experimental data and for performing a better error analysis.

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Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Capacitively Coupled Resistivity Imaging Measurements on Rock Samples

Uhlemann¹,

Kuras²,

Green³

2012

Proceedings

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“…Coupling is then largely confined to the surface of the plate and, on the scale of the four-point array, the point-pole condition is approximately fulfilled so that a DC geometric factor can be calculated. Another conceivable type of capacitive sensor is the capacitive line antenna (Timofeev et al, 1994), but interpretation of measurements is not trivial as the capacitance of such antennas is evenly distributed across their entire length (Kuras et al, 2006). In this paper, we will therefore focus on the use of plate-wire sensors.…”

Section: The Capacitive Resistivity Techniquementioning

confidence: 99%

“…Methodology, basic physics and the advantages and limitations of capacitive resistivity were the subject of a recent paper by the same authors (Kuras et al, 2006). …”

Section: The Capacitive Resistivity Techniquementioning

confidence: 99%

“…Capacitive resistivity (CR) is an emerging geophysical technique (Kuras et al, 2006) with the potential to overcome both problems. Suitable instrumentation has been available both at a research level and commercially for some time; however it appears that many basic issues surrounding mobile capacitive measurements have not yet been 5 addressed in the published literature.…”

Section: Introductionmentioning

confidence: 99%

“…the phase-sensitive apparent resistivity reduces to the classical DC expression for the in-phase component of the transfer impedance (Tabbagh et al, 1993;Kuras et al, 2006).…”

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confidence: 99%

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Capacitive Resistivity Imaging with Towed Arrays

Kuras

Meldrum

Beamish

et al. 2007

JEEG

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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.

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Monitoring rock freezing and thawing by novel geoelectrical and acoustic techniques

et al. 2016

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Automated monitoring of freeze‐thaw cycles and fracture propagation in mountain rockwalls is needed to provide early warning about rockfall hazards. Conventional geoelectrical methods such as electrical resistivity tomography (ERT) are limited by large and variable ohmic contact resistances, requiring galvanic coupling with metal electrodes inserted into holes drilled into rock, and which can be loosened by rock weathering. We report a novel experimental methodology that combined capacitive resistivity imaging (CRI), ERT, and microseismic event recording to monitor freeze‐thaw of six blocks of hard and soft limestones under conditions simulating an active layer above permafrost and seasonally frozen rock in a nonpermafrost environment. Our results demonstrate that the CRI method is highly sensitive to freeze‐thaw processes; it yields property information equivalent to that obtained with conventional ERT and offers a viable route for nongalvanic long‐term geoelectrical monitoring, extending the benefits of the methodology to soft/hard rock environments. Contact impedances achieved with CRI are less affected by seasonal temperature changes, the aggregate state of the pore water (liquid or frozen), and the presence of low‐porosity rock with high matrix resistivities than those achieved with ERT. Microseismic monitoring has the advantage over acoustic emissions that events were recorded in relevant field distances of meters to decameters from cracking events. For the first time we recorded about 1000 microcracking events and clustered them in four groups according to frequency and waveform. Compared to previous studies, mainly on ice‐cracking in glaciers, the groups are attributed to single‐ or multiple‐stage cracking events such as crack coalescence.

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Fundamentals of the capacitive resistivity technique

Cited by 116 publications

References 21 publications

Numerical Simulation of Capacitively Coupled Resistivity Imaging Measurements on Rock Samples

Numerical Simulation of Capacitively Coupled Resistivity Imaging Measurements on Rock Samples

Capacitive Resistivity Imaging with Towed Arrays

Monitoring rock freezing and thawing by novel geoelectrical and acoustic techniques

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