Capacitive Resistivity Research Articles

Near-Surface Geophysical Characterization of a Marble Deposit to Promote a Sustainable Small-Scale Mining

Small-scale mining (SSM) is responsible for almost all the production of non-metallic minerals in the world and represents around 80% of the mining in Brazil. The lack of direct geological information increases the level of uncertainty associated with the exploratory process, compromises mine planning, limits mineral extraction, and contributes to maximizing environmental issues. In this research, near-surface geophysical methods, including Electrical Resistivity, Capacitive Resistivity, Ground Penetrating Radar (GPR), and Transient Electromagnetic (TEM), were applied to characterize a marble deposit in an SSM located in the Campos do Jordão region, São Paulo state, southeast Brazil. The geophysical methods used provide indirect information about the subsurface geology based on the contrast in electrical and electromagnetic properties. Resistivity results show the efficiency of locating marble deposits, as well as fracture zones. GPR profiles allowed for the investigation of the structural heterogeneities in the subsurface. Geophysical data and lithological information from drill holes were integrated into Micromine software and guided the development of a geological model and a conceptual pit model. The information inferred from the pit modeling allowed us to analyze the potential of the deposit and should be used to assist in developing sustainable mining planning. The results of this work demonstrate that the investment in geophysical research can support the modernization of an SSM and contribute to more sustainable and productive mining.

Deep Neural Network-based Current and Voltage Prediction Models for Digital Measuring Unit of Capacitive Resistivity Underground Imaging Transmitter Subsystem

Deep Neural Network-based Current and Voltage Prediction Models for Digital Measuring Unit of Capacitive Resistivity Underground Imaging Transmitter Subsystem

Capacitive Resistivity Method Applied to the Environmental Diagnosis and Management of Contaminated Area of Gas Station

This article presents a case study of fuel underground contamination where the geophysical method was applied to support for decision making regarding environmental management activities. The application of geophysical methods that measure electrical resistivity in the study of contaminated areas and their correlations with organic contaminants are discussed, in addition to the presentation of theoretical and practical aspects of Capacitive Resistivity (CR) method. The importance of this work is based on the evaluation of the potential for identification of free phase of organic contaminant by the capacitive method and the assessment of the effectiveness of the remediation implemented through the geophysical data obtained. The method applied was able to identify the highest electrical resistivities related to fuel in the subsurface and indicated the inefficiency of the current remediation by the inadequate positioning of the extraction wells and the inaccuracies in the monitoring of underground contamination and allowed the proposition of recommendations related to management of the case based on geophysical information. From results, it is concluded that the Capacitive Resistivity method can be applied in similar cases of leaks in gas stations to diagnose contamination and to guide the adoption of more appropriate actions of environmental management.

Assessing the environmental impact of oil spills in beach environments: a case study using the Capacitive Resistivity Method

The accident involving oil spill that occurred on the Brazilian coast in 2019 reached 2,880 km in extension, and more than 200 tons of oily material was removed from coastal environments in the northeast of the country in about five months. In the impact on beach environment there may still be non-visible residues and its by-products in subsurface, so that geophysical prospecting can be the suitable to evaluate the presence of remaining material. The evolution of environmental studies has required new research technologies. Geophysical methods have shown to be efficient in environmentalstudies, with the use of relatively new methods in Brazil that provide results with excellent coverage in the area and quickly. Among these methods stands out the Capacitive Resistivity Method. Environmental research work with this method has been reported with good results, but it is necessary to take into account the operational physical bases of the method so that the data is reliable. This work presents the results of tests carried out in a beach environment that was affected by oil. This environment is characterized by a medium of high conductivity, where data acquisition with equipment configured with smaller dipolar cables results in extremely noisy data. On the other hand, the configuration with larger dipolar cables allowed the transmission of higher electrical current to the ground resulting in the acquisition of good quality data. The results showed that there are no more indications of oil residues on the beach studied.

Multi-Parametric Imaging of Etruscan Chamber Tombs: Grotte Di Castro Case Study (Italy)

A multi-parametric approach that involves the use of different geophysical methods coupled with geochemical data allowed us to identify undiscovered archeological burials in a funerary area of the Grotte di Castro Etruscan settlement. In particular, we tested the suitability of the capacitive resistivity method and the presence of Radon in soil for the identification of burials calibrating their outcomes over coincident survey profiles with standard geophysical techniques routinely applied for archaeological prospections. Soil Radon data were acquired both in a grid and along a profile to highlight anomalous gas concentrations, whereas electrical resistivity and ground-penetrating radar measurements were conducted on overlapping profiles to depict the electrical and electromagnetic subsurface distribution. Data integration showed a series of anomalies, suggesting the presence of multiple burials starting from a depth of approximately 1.5 m below the terrain surface. Slight anomalies of Radon in the soil were found to correspond to most of the recovered geophysical ones. Our results pointed out the effectiveness of geophysical method integration in archeological prospecting with the novelty of the joint use of Radon in soil measurements and capacitive resistivity tomography. The latter provided reliable results and can be considered as a standalone technique in archaeological surveys.

Изучение талика под малым водотоком методом бесконтактной электроразведки

Изучение талика под малым водотоком методом бесконтактной электроразведки

Determining the Field of Application of the Noncontact Resistivity Technique

The resistivity method is widely used in shallow surface geophysics. Capacitive resistivity is one of techniques that extend the use of the resistivity method for an environment where galvanic coupling of electrodes is difficult, for instance, frozen ground, hard rocks, and engineered structures (roads, railways etc.). This technique allows rapid field work without galvanic coupling electrodes. The main problem is the complicated calculation of forward resistivity for a simple model. The limitations on the use of the technique are not clear in the theoretical and practical aspects in the results. The authors determined the limits of the electrical properties and distances for capacity resistivity.

The determination of usability area for capacitive resistivity measurements

Resistivity method is widely used in shallow surface geophysics. Capacitive resistivity is one of techniques which help to extend usage of resistivity method for environmentc where galvanic coupling of electrodes is difficult, for instance, frozen ground, hard rocks and engineered structures (roads, railways and others). This technique allows fast field work without galvanic coupling electrodes. The main problem is complicated calculation of forward resistivity for simple model. In results, the limitations to the usage of the technique are not clear in theoretical and practical aspects. The authors determinate the limits of electrical properties and distances for capacity resistivity.

The study of talik under a small watercourse by the capacitive resistivity method.

The study of talik under a small watercourse by the capacitive resistivity method.

Monitoring rock freezing and thawing by novel geoelectrical and acoustic techniques

AbstractAutomated 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.

Examining the influence of vegetation on slope hydrology in Hong Kong using the capacitive resistivity technique

Vegetation essentially has both beneficial and detrimental hydrological effects on slope stability, and the balance between these effects changes throughout the year. For engineers considering vegetation as an ecotechnological solution to slope instability, it is therefore necessary to understand how the net hydrological effect varies with local weather conditions. In this study, year-round field monitoring was carried out to examine the influence of a native plant on slope hydrology in Hong Kong using the capacitive resistivity technique and a newly developed line-electrode resistivity array. The measured soil resistivity was used to infer the soil moisture conditions on the slopes. The results show that vegetation generally has a strong influence on soil moisture although this effect varies among seasons. During the summer time, vegetation increases the soil moisture if compared with the bare slope. This is mainly due to the high precipitation, most of which enters the vegetated slope because of the increased permeability and infiltration rate caused by the vegetation. During the autumn time, the influence of vegetation evapotranspiration on slope hydrology becomes noticeable mainly because of the low precipitation (monthly less than 100mm) and the relatively high potential evapotranspiration (monthly around 100mm). In dry and cold winter, resistivity measurements suggest that the vegetation helps retain the soil water. In the following spring, difference in the soil moisture in bare and vegetated slopes is gradually wiped out because of the frequent rainfall. When the monthly rainfall reaches ~400mm in early summer, the influence of vegetation on slope hydrology (soil moisture) completely disappears.

Geophysical characterization of permafrost terrain at Iqaluit International Airport, Nunavut

Iqaluit International Airport presently suffers from instabilities and subsidence along its runway, taxiways and apron. In particular, asphalt surfaces are significantly impacted by settlement and cracking. These instabilities may be related to permafrost, permafrost degradation and associated drainage conditions. Low induction number electromagnetic measurements along with galvanic and capacitive electrical resistivity surveys were performed over selected areas within the airport boundary and in the near vicinity to assist with permafrost characterization and to investigate active permafrost processes. Electrical resistivity images suggest distinct electrical signatures for different terrain units and sediment types, and for ice-rich material including ice wedges. Anomalous regions are identified that are coincident with localized settlement problems. Repeated resistivity maps reveal seasonal changes indicative of high unfrozen water content and freeze/thaw of groundwater beneath airport infrastructure in distinct regions related to surficial geology. Even with continuous permafrost and cold permafrost temperatures, the resistivity models reveal anomalously conductive material at depth that is not obviously correlated to mapped surficial sediments and that may represent thaw susceptible sediments or significant unfrozen water content.

Numerical Simulations of Capacitive Resistivity Imaging (CRI) Measurements

ABSTRACTElectrical resistivity tomography (ERT) is a well‐developed geophysical technique that is used to study a variety of geoscientific problems. In recent years it has been applied to the study of permafrost processes at both field and laboratory scale. However, highly resistive surface conditions limit its applicability due to high and variable contact resistances. The use of capacitively coupled sensors is expected to overcome this problem by providing a steady contact impedance regime. Although the theory of capacitive resistivity imaging (CRI) is well understood, a point‐pole approximation of the sensors is typically used to show the similarity between CRI and ERT. Due to their nature, capacitive sensors cannot be designed as point‐poles as they require a finite extent. This paper assesses the effects the finite size of sensors has on the applicability of CRI theory and aims to provide an improved understanding of the measured data. We employ finite‐element numerical modelling to simulate CRI measurements over a homogeneous halfspace and on a finite rock sample. The results of a parameter study over a homogeneous halfspace are compared to an analytical solution. Observed discrepancies between the two solutions clearly indicate that large sensor sizes and small sensor separations violate the point‐pole assumption of the analytical solution. In terms of data interpretation, this dictates that sensor separations smaller than twice the sensor size have to be avoided in order to remain below a generic error threshold of 5%. We show that sensor elevation, halfspace resistivity, halfspace permittivity, and measurement frequency have only minor effects on the discrepancy between simulation and analytical solution. The simulation of sequential CRI measurements on a finite rock sample suggests that, in line with expectations, the measured signals lie mainly in the 4th quadrant of the complex plane. However, we can also observe data with negative geometric factors, which are related to uncommon array. A comparison between simulated and measured data showed very good agreement; it validated the simulations and explained the measured data acquired using a prototype multisensor CRI system. We show that a comparison of simulated and measured imaginary parts of the transfer impedance can be used to assess CRI measurement errors. Our work demonstrates that finite‐element numerical modelling of CRI measurements is a valuable tool with which to define limitations on array design and to assess data quality.

Capacitive resistivity inversion using effective dipole lengths for line antennas

Non-contacting capacitively-coupled resistivity (CCR) surveys find application in permafrost investigations and investigations over engineered surfaces. However, we observe discrepancies between line-antenna CCR data and galvanic resistivity (GR) data. Inverse models recovered from the different data types exhibit differences in both resistivity magnitude and structure. We apply and test the concept of effective dipole length for line-antenna CCR data collected over permafrost terrain in Iqaluit, Nunavut. We compare inversions of corrected CCR data to the GR counterpart. Results show that correcting CCR data with an effective dipole length of 80% of the physical antenna length results in a resistivity model most in accordance with the GR model. After correction, the CCR model does not precisely emulate the GR model; potential sources of remaining discrepancy are incomplete representation of the line-antenna nature of the CCR data and the realities of field data acquisition including significantly different noise levels and the potential violation of CCR operating conditions.

Improvements in crosshole GPR full-waveform inversion and application on data measured at the Boise Hydrogeophysics Research Site

Abstract Crosshole ground penetrating radar (GPR) tomography has been widely used and has the potential to improve the obtained subsurface models due to its high spatial resolution compared to other methods. Recent advances in full-waveform inversion of crosshole GPR data show that higher resolution images can be obtained compared to conventional ray-based GPR inversion because it can exploit all information present in the observed data. Since the first application of full-waveform inversion on synthetic and experimental GPR data, the algorithm has been significantly improved by extending the scalar to a vectorial approach, and changing the stepped permittivity and conductivity update into a simultaneous update. Here, we introduce new normalized gradients that do not depend on the number of sources and receivers which enable a comparison of the gradients and step lengths for different crosshole survey layouts. An experimental data set acquired at the Boise Hydrogeophysics Research Site is inverted using different source–receiver setups and the obtained permittivity and conductivity images, remaining gradients and final misfits are compared for the different versions of the full-waveform inversion. Moreover, different versions of the full-waveform inversion are applied to obtain an overview of all improvements. Most improvements result in a reducing final misfit between the measured and synthetic data and a reducing remaining gradient at the final iteration. Regions with relatively high remaining gradient amplitudes indicate less reliable inversion results. Comparison of the final full-waveform inversion results with Neutron–Neutron porosity log data and capacitive resistivity log data show considerably higher spatial frequencies for the logging data compared to the full-waveform inversion results. To enable a better comparison, we estimated a simple wavenumber filter and the full-waveform inversion results show an improved fit with the logging data. This work shows the potential of full-waveform inversion as an advanced method that can provide high resolution images to improve hydrological models.

Inverting Capacitive Resistivity (Line Electrode) Measurements with Direct Current Inversion Programs

The capacitive resistivity (CR) method is a time‐ and labor‐saving alternative to traditional direct current (DC) resistivity methods. The line electrode variant of CR suffers from the absence of data inversion programs as available for the DC resistivity method. Direct current inversion programs were applied to determine the resistivity distribution from CR measurements using an approximately equivalent four‐point dipole–dipole configuration. We optimized configurations to minimize the systematic error applying DC inversion programs to CR, using data based on the comparison of the two‐dimensional sensitivities of the proposed DC approximations. The optimal four‐point dipole–dipole geometry has a dipole length of 80%.

Applications of capacitive resistivity measurements with the OhmMapper

Applications of capacitive resistivity measurements with the OhmMapper

Contribution of 3-D electrical resistivity tomography for landmines detection

Abstract. Landmines are a type of inexpensive weapons widely used in the pre-conflicted areas in many countries worldwide. The two main types are the metallic and non-metallic (mostly plastic) landmines. They are most commonly investigated by magnetic, ground penetrating radar (GPR), and metal detector (MD) techniques. These geophysical techniques however have significant limitations in resolving the non-metallic landmines and wherever the host materials are conductive. In this work, the 3-D electric resistivity tomography (ERT) technique is evaluated as an alternative and/or confirmation detection system for both landmine types, which are buried in different soil conditions and at different depths. This can be achieved using the capacitive resistivity imaging system, which does not need direct contact with the ground surface. Synthetic models for each case have been introduced using metallic and non-metallic bodies buried in wet and dry environments. The inversion results using the L1 norm least-squares optimization method tend to produce robust blocky models of the landmine body. The dipole axial and the dipole equatorial arrays tend to have the most favorable geometry by applying dynamic capacitive electrode and they show significant signal strength for data sets with up to 5% noise. Increasing the burial depth relative to the electrode spacing as well as the noise percentage in the resistivity data is crucial in resolving the landmines at different environments. The landmine with dimension and burial depth of one electrode separation unit is over estimated while the spatial resolutions decrease as the burial depth and noise percentage increase.

Shallow Inductive Electric Field Response Measured with Capacitive Sensors

SummaryModelling software developed and results from a prototype instrument shows that a new Capacitive Array Resistivity with Inductive Source (CARIS) method being developed has potential for detecting both conductive and resistive objects and near surface conductivity contrasts. Detecting buried resistive objects has possible application in near surface exploration. Applications could include identification and mapping of chromite and mineral containing quartz veins as well as alteration, silicification. It also shows potential for other near surface applications such as UXO, archaeology, void detection, pipe delineation, or fracture detection. A prototype 100kHz CARIS instrument has been designed and built. The prototype CARIS instrument has been tested with highly repetitive results under laboratory conditions, showing good comparison with expected results from modelling. Results have shown the ability of the system to reliably detect resistive objects within a conductive uniform half-space (salt water) environment. The CARIS system has also undergone preliminary testing in the field. Initial results from field testing show high repeatability but also high lateral variability. This appears to be due to sensitivity to near surface moisture and soil consolidation contrasts. Currently a larger second prototype operating at 5kHz is in production aimed at reducing the sensitivity to soil effects moisture and consolidation effects and increasing the depth of investigation.

Capacitive Resistivity Imaging with Towed Arrays

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 [Formula: see text]. 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 (electrical resistivity tomography); it therefore widens the scope of electrical imaging surveys to environments where the conventional methodology would be impractical.