Potential Of Electrical Resistivity Tomography Research Articles

Early detection of deep-seated smouldering fires in wood waste storage using ERT

Incidents of waste and biofuel fires are common at all stages of the waste recycling chain and have grave implications for business, employees, firefighters, society, and environment. An early detection of waste and biofuel fires in the smouldering stage could save precious lives, resources, and our environment. Existing fire detection methodologies e.g. handheld temperature sensors, IR cameras, gas sensors, and video and satellite-based monitoring techniques have inherent limitations to efficiently detect smouldering fires. An attempt was made to explore the potential of electrical resistivity tomography (ERT) as an alternate tool to address the problem. In the experiments an externally powered resistive wire was employed to initiate the smouldering fire inside the test material (wood pellets, wood shavings, wood fines). Time series of ERT that followed the initiation and development of smouldering were recorded using an automated monitoring instrument setup. The actual geometry of the experimental sample container and electrode setup was integrated in the 3D finite element method (FEM) model grid to perform inverse numerical modelling (inversion) and to develop resistivity tomographic images. The study shows a sharp increase in ratio of resistivity (R/Ro ≥ 50 %) in the test material in the region of smouldering hotspot and demonstrates the potential use of ERT technique for the detection of smouldering hotspots in silos and pile storage of organic material such as wood-based fuels, wood waste, coal, municipal solid waste (MSW), recyclables etc. More research is however required for enabling the use of this technique at the practical scale for different storage conditions.

Capabilities and limitations of electrical resistivity tomography for mapping and surveying hillfort fortifications

AbstractHillforts are fortified archaeological sites built from the Neolithic to Early Middle Ages within the area of Europe. They were usually surrounded by fortifications consisting of various combinations of ramparts and ditches, which today constitute their most striking remains. Although magnetometry surveys are commonly used for spatial identification of ramparts and ditches, a different method must be employed for directly obtaining depth information. Hence, we evaluate the potential of electrical resistivity tomography (ERT) for surveying hillfort fortifications. Within three hillforts of different ages in the Czech Republic, we investigated various features affecting the imaging ability of ERT, including bedrock type, building material, present‐day condition of fortification, impact of past or recent agricultural activities, and field settings of the ERT method. Supported by additional information from magnetometry and electromagnetic surveys, the results show that ERT is most applicable in cases of stony ramparts, ditches carved into rocky bedrock or well‐preserved earthen ramparts. Poorer results were achieved upon active and/or recently active agricultural lands, where fortifications have been gradually destroyed by ploughing. The remains of stony ramparts remained distinguishable in the latter case, but mere traces of earthen ramparts and ditches were invisible to ERT due to mixing of fortification material with on‐site soil. ERT is a unique method for detailed investigation of both ramparts and ditches by which a structure and its extent can be evaluated to indicate the function of a settlement and obtain information about former environmental conditions, population, land use and/or human–environmental interaction.

Time‐intensive geoelectrical monitoring under winter wheat

ABSTRACTSeveral studies have explored the potential of electrical resistivity tomography to monitor changes in soil moisture associated with the root water uptake of different crops. Such studies usually use a set of limited below‐ground measurements throughout the growth season but are often unable to get a complete picture of the dynamics of the processes. With the development of high‐throughput phenotyping platforms, we now have the capability to collect more frequent above‐ground measurements, such as canopy cover, enabling the comparison with below‐ground data. In this study hourly direct‐current resistivity data were collected under the Field Scanalyzer platform at Rothamsted Research with different winter wheat varieties and nitrogen treatments in 2018 and 2019. Results from both years demonstrate the importance of applying the temperature correction to interpret hourly electrical conductivity data. Crops which received larger amounts of nitrogen showed larger canopy cover and more rapid changes in electrical conductivity, especially during large rainfall events. The varieties showed contrasted heights although this does not appear to have influenced electrical conductivity dynamics. The daily cyclic component of the electrical conductivity signal was extracted by decomposing the time series. A shift in this daily component was observed during the growth season. For crops with appreciable difference in canopy cover, high‐frequency direct‐current resistivity monitoring was able to distinguish the different below‐ground behaviours. The results also highlight how coarse temporal sampling may affect interpretation of resistivity data from crop monitoring studies.

English

The use of DC electrical method in baryte mineral exploration has been investigated in Buruku northeast of Markurdi, Nigeria. The objective of the study was to investigate the suitability and potential of electrical resistivity tomography (ERT) combined with vertical electrical sounding (VES) surveys in baryte mineral exploration over known deposits. Results show that the interpreted layer resistivities correlate with the 2-D observations. The study delineated averagely 28 m deep symmetrically mound-shaped resistive anomalies (1500 to 5500 Ωm) encased within low resistive sandstone formation along prospective traverses. These responses are characteristics of probable vein structures associated with baryte mineralization. Two dominant E-W and NW-SE resistivity anomaly trends were delineated. The E-W trends were more prominent and persistent than the NW-SE. They are 25 to 50 m wide and stretches to over 300 m in length. The association of mineralized veins with these trends suggests that the veins must be of early Cretaceous age. These mineralized veins correlate with locations of known baryte deposits in the prospect area which hitherto, have been exploited by artisan miners. This is an obvious indication of the utility and resolution of dc electrical method in baryte mineral exploration in the area. Key words: Electrical resistivity tomography (ERT), Vertical electrical sounding (VES), resistivity, Baryte, vein and mineralization.

Potential of Electrical Resistivity Tomography to Detect Fault Zones in Limestone and Argillaceous Formations in the Experimental Platform of Tournemire, France

The Experimental platform of Tournemire (Aveyron, France) developed by IRSN (French Institute for Radiological Protection and Nuclear Safety) is located in a tunnel excavated in a clay-rock formation interbedded between two limestone formations. A well-identified regional fault crosscuts this subhorizontal sedimentary succession, and a subvertical secondary fault zone is intercepted in the clay-rock by drifts and boreholes in the tunnel at a depth of about 250 m. A 2D electrical resistivity survey was carried out along a 2.5 km baseline, and a takeout of 40 m was used to assess the potential of this method to detect faults from the ground surface. In the 300 m-thick zone investigated by the survey, electrical resistivity images reveal several subvertical low-resistivity discontinuities. One of these discontinuities corresponds to the position of the Cernon fault, a major regional fault. One of the subvertical conductive discontinuities crossing the upper limestone formation is consistent with the prolongation towards the ground surface of the secondary fault zone identified in the clay-rock formation from the tunnel. Moreover, this secondary fault zone corresponds to the upward prolongation of a subvertical fault identified in the lower limestone using a 3D high-resolution seismic reflection survey. This type of large-scale electrical resistivity survey is therefore a useful tool for identifying faults in superficial layers from the ground surface and is complementary to 3D seismic reflection surveys.

Potential of electrical resistivity tomography to infer aquifer transport characteristics from tracer studies: A synthetic case study

With time‐lapse electrical resistivity tomography (ERT), transport processes in the subsurface can be imaged and monitored. The information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability. Difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ERT is generally underdetermined and that ERT data acquisition is often limited to two‐dimensional (2‐D) image planes. To address this problem, we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2‐D image plane perpendicular to the mean flow direction using time‐lapse ERT. The tracer breakthrough patterns in the image plane were interpreted using equivalent transport models: an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves. Equivalent parameters derived from simulated and from ERT inverted concentrations showed a good agreement, which demonstrates the potential of ERT to characterize subsurface transport. Using first‐order approximate solutions of stochastic flow and transport equations, equivalent model parameters and their spatial variability were interpreted in terms of the local‐scale dispersion and the spatial variability of the hydraulic conductivity. The spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related. Consequently, the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions, which can be observed with sufficiently high spatial resolution using ERT.