Electrical Resistivity Tomography Method Research Articles

Frequency domain electromagnetic calibration for improved detection of sand intrusions in river embankments

Sand intrusions pose significant risks to river embankments due to potential flow pathways that can lead to instability during flood events. Visual inspection is a first step to recognize critical segments, but it does not deliver information about the subsurface. In this context, the electromagnetic induction (EMI) technique is a useful method for preliminary zoning at regional scale while the electrical resistivity tomography (ERT) method, widely used for hydrological purposes, is considered among the most reliable techniques for local subsurface imaging. A major sand intrusion within the levees of the Brenta River, located near Venice (northern Italy), resulted in water seeping during seasonal floods and posed severe threats to embankment stability. ERT and EMI techniques, along with geotechnical investigations, were the best survey choices to address the problem. Resistivity profiling successfully imaged the sand body geometry within and underneath the levee, and results correlated nicely with borehole stratigraphy. A first multiarray EMI device, which represented a faster and less expensive survey, was deployed to map further anomalies along nearby levees, but results were not satisfactory because the inverted profile failed to image the known intrusion. A second multiarray EMI device, with larger coil spacing, was also tested. Although it performed better in detecting the intrusion, results were still below expectations. A calibration procedure based on Pearson's coefficients and using ERT as a reference was then devised and implemented to correct the EMI data prior to carrying out inversion. The procedure was successful for both EMI data sets, leading to realistic subsurface resistivity in the inverted sections. EMI measurements could then be recovered and interpreted correctly to estimate subsurface textures. The possibility of calibrating EMI data and obtaining subsurface resistivity images comparable to standard ERT profiling is an important improvement for cost-effective EMI surveying of river embankments to mitigate flood hazards.

Integration of Ground Penetrating Radar and Electrical Resistivity Methods to Investigate Subsurface Features at Kish Archaeological site, Babylon, Iraq

Several geophysical techniques, including magnetic, Electrical Resistivity Imaging (ERI), and Ground Penetrating Radar (GPR), have been used to investigate archaeological features because they are non-destructive and inexpensive compared to traditional methods such as excavation. GPR has been used in the Governorate of Babylon, Kish archeological site to investigate the subsurface ancient features.The GPR survey carried out on three parallel profiles. The length of each profile is 29 m and the spacing between each adjacent profile is 15 meters. The antennas 450 MHz and 750 MHz were used. The data was processed using GPR SliceV7 software. The GPR profiles indicate the presence of buried features, which may be an ancient wall. The wall is buried at a depth range between 0.5 and 3 m. Outside the study area, some part of the wall is visible on the surface. Three Electrical resistivity image (ERI) profiles (1, 2 and 3) were carried out by using wenner array to check the main features detected by GPR method. The ERI results are confirmed the GPR profiles (1, 2, and 3). Both methods indicate the existence of an ancient wall trending NW-SE. The thickness of the wall is approximately 3m and is located at distance 7.5-10.5 meters at profile 1 in the south and at distance 10-13 m in profiles 2 and 3. The depth of the wall ranges from 3–3.5 m. Another deep wall was also detected in the GPR profile 1 and in the three profiles of ERI method. The current work confirmed the importance of using ERI method with GPR method to investigate shallow subsurface features.

Temporal and spatial distribution patterns of upper saline plumes and seawater-groundwater exchange under tidal effect

Under tidal influence, an active exchange process occurs between seawater and groundwater in the coastal aquifer system. However, in-situ studies and research on the temporal and spatial distribution patterns of upper saline plumes (USPs) and seawater-groundwater exchange process are lacking. In this study, we selected the Shilaoren beach in Qingdao as the study area, and used pseudo-3D electrical resistivity tomography (ERT) and hydrogeological measurement methods to monitor the spatial distribution of groundwater salinity and the seawater and groundwater exchange process. We found that during the ebbing tide, USPs were divided into several smaller USPs driven by groundwater discharge. Subsequently, during the flooding tide, high-salinity seawater recharge was observed, and several smaller USPs gradually aggregated into a complete USP. In coastal aquifers, the exchange of seawater and groundwater not only occurs through the beach surface and seepage face, but also includes high-permeability underground channels. Seawater and groundwater exchange occurs more rapidly through these underground channels randomly distributed at depth, which also leads to spatial differences in the seawater and groundwater exchange process. Additionally, affected by underground channels, the groundwater discharge flux shows spatial heterogeneity. In areas with underground channels, the groundwater discharge flux significantly increases. Therefore, the non-seepage face area has a similar groundwater discharge flux to the main groundwater discharge area, namely, the seepage face. In the intertidal zone of the study area (70 × 60 m), the total groundwater discharge flux through the seepage face is 3407.6 m3, and no significant difference is observed in the groundwater discharge flux at various parts of the seepage face. In the non-seepage face area, the groundwater discharge is highly spatially heterogeneous; the total groundwater discharge flux is 3252.0 m3, and approximately 60% of this occurs through densely developed underground channels.

Characterization of site contaminated with petroleum-effluents and evaluation of neighbouring groundwater quality using combined electrical resistivity tomography and geochemical methods

Characterization of site contaminated with petroleum-effluents and evaluation of neighbouring groundwater quality using combined electrical resistivity tomography and geochemical methods

Geophysically guided well siting at the Aluto-Langano geothermal reservoir

Volcano-hosted high-temperature geothermal reservoirs are powerful resources for green electricity generation. In regions where such resources are available, geothermal energy often provides a large share of a country’s total power generation capacity. Sustainable geothermal energy utilization depends on the successful siting of geothermal wells, which in turn depends on prior geophysical subsurface imaging and reservoir characterization. Electromagnetic resistivity imaging methods have proven to be a key tool for characterizing magma-driven geothermal systems because resistivity is sensitive to the presence of melt and clays that form through hydrothermal alteration. Special emphasis is often given to the “clay cap,” which forms on top of hydrothermal reservoirs along the flow paths of convecting geothermal fluids. As an example, the Aluto-Langano volcanic geothermal field in Ethiopia is covered with 178 densely spaced magnetotelluric (MT) stations. The 3D electrical conductivity model derived from the MT data images the magma body that acts as a heat source of the geothermal system, controlling geothermal convection and formation of alteration zones (commonly referred to as clay cap) atop the geothermal reservoir. Detailed 3D imaging of the clay cap topography can provide direct insight into hydrothermal flow patterns and help identify potential “upflow” zones. At Aluto all productive geothermal wells are drilled into zones of clay cap thinning and updoming, which is indicative of underlying hydrothermal upflow zones. In contrast, nonproductive wells are drilled into zones of clay cap thickening and lowering, which is an indicator for underlying “outflow” zones and cooling. This observation is linked to fundamental characteristics of volcano-hosted systems and can likely be adapted to other geothermal fields where sufficiently detailed MT surveys are available. Therefore, high-resolution 3D electromagnetic imaging of hydrothermal alteration products (clay caps) can be used to infer the hydrothermal flow patterns in geothermal reservoirs and contribute to derisking geothermal drilling projects.

A Positive Data Extraction Method for Electrical Impedance Tomography (EIT) Based on the Novel MSA-Net

The nonlinear and ill-posed Electrical Impedance Tomography (EIT) inverse problem leads to reconstructed images with distortion and low resolution. A positive data extraction method based on the deep learning is proposed in this study. This method realizes the accurate classification of the positive data and the general data in voltage measurements through a deep learning network called Multi Scale Attention Network (MSA-Net). The positive data is used for image reconstruction to improve the imaging quality. Multi scale feature extraction, residual learning and attention mechanism are introduced in the MSA-Net to improve classification accuracy. The Linear Back Projection (LBP) algorithm and the Tikhonov Regularization (TR) algorithm are used to verify the effectiveness of the proposed method. Both simulation and experiment are conducted around imaging of bubble flow. The simulation results indicate that there are fewer artifacts in the reconstructed images using the positive data of MSA-Net, and the shape and position of the bubbles can be better described. Moreover, the imaging quality of experimental samples can also be effectively improved. The existing test results preliminarily confirm that the distribution of the positive data and the general data in voltage measurements is related to the position of bubbles in the measurement domain.

Groundwater monitoring and specific yield estimation using time-lapse electrical resistivity imaging and machine learning

This paper presents an alternative method for monitoring groundwater levels and estimating specific yields of an unconfined aquifer under different seasonal conditions. The approach employs the Time-Lapse Electrical Resistivity Imaging (TL-ERI) method and machine learning-based time series clustering. A TL-ERI survey was conducted at ten sites (WS01-WS10 sites) throughout the dry and wet seasons, with five-time measurements collected for each site, in the Taichung-Nantou Basin along the Wu River, Central Taiwan. The obtained resistivity raw data was inverted and converted into normalized water content values using Archie’s law, followed by applying the Van Genuchten (VG) model for the Soil Water Characteristic Curve to estimate the Groundwater Level (GWL), and estimated the theoretical specific yield (Sy) by computing the difference between the saturated and residual water contents of the fitted VG model. In addition, the specific yield capacity (Sc), representing the nature of the storage capacity in the aquifer, was also calculated. The results showed that this approach was able to estimate those hydrogeological parameters. The spatial distribution of the GWL reveals that during the dry-wet seasons from February to July, there was a high GWL that extended from southeast to northwest. Conversely, during the wet-dry seasons from July to October, the high GWL shrank, which can be attributed to recharge variations from rainfall events. The determined spatial distribution of Sy and Sc fall within the range of 0.03–0.24 and 0.14–0.25, respectively. To quantitatively establish areas of similar groundwater level changes along with the VG model parameter variations during the study period, a Time series Clustering analysis (TSC) was performed by utilizing Hierarchical Agglomerative Clustering (HAC). The findings suggest that the WS03 site is a promising area for further investigation due to its highest Sc value with a slight change in groundwater levels during the dry and wet seasons. This study brings an advanced development of the geoelectrical method to estimate regional hydrogeological parameters in an area with limited available groundwater observation wells, in different seasonal conditions for groundwater management purposes.

Urban geophysical exploration: case study in Chengdu International Bio-City

Abstract Understanding the shallow geological structure of urban areas is crucial for effective planning and development of underground spaces. Geophysical methods that are well-suited for site-specific investigation and have robustly anti-interference capabilities can provide important geological information for urban areas. In support of investigating the 3D geological structure of the shallow subsurface in Chengdu International Bio-City, a geophysical exploration study was conducted using three methods: the electrical resistivity tomography (ERT), micro-seismic exploration and opposing-coil transient electromagnetic method (OCTEM). Results from the study showed that the ERT method was greatly affected by local high-resistance bodies, construction sites and industrial currents, therefore leading to poor detection results that did not match well with the area’s layered structure characteristics. The micro-seismic exploration method showed good layering effects and correlation with the drilling data in the elevation range of ∼350 to 436 m, but poor layering effects and low correlation with drilling data in the elevation range of ∼235 to 350 m, with relatively slow construction efficiency. The OCTEM showed good correlation with the drilling data for shallow depths up to 200 m and good identification capabilities for gypsum and mudstone in the area. Additionally, the instrument’s anti-interference ability was suitable for complex urban conditions. Thus, OCTEM was selected for the area-based exploration with a 100 × 10 m grid, rapidly obtaining 3D resistivity information for depths up to 200 m in the study area. By integrating the 3D resistivity information with known engineering geological information, a comprehensive 3D geological model of the study area was created.

Image reconstruction method for electrical impedance tomography based on RBF and attention mechanism

Electrical impedance tomography (EIT) is an imaging technology for estimating the conductivity change for the measured field of the human body. However, because EIT image reconstruction is severely ill-posed and nonlinear inverse problem, the reconstructed image based on traditional algorithm is lower accurate with obscure boundaries and lots of artifacts. In order to improve the accuracy of reconstructed image, an EIT image reconstruction method based on RBF and attention mechanism is proposed in this paper. The proposed RCU-Net network architecture consists of two sub-networks: RBF and CBAM-UNet. The RBF neural network accomplishes the nonlinear mapping between the boundary voltages and conductivity distribution values. The CBAM-UNet combining attention mechanism CBAM with U-Net makes further processing for the resulting images to obtain more sharp and explicit images. RCU-Net was trained and tested on the simulated dataset created by EIDORS platform. The experiment reveals that the proposed method outperforms the traditional methods in distinguishing multi-target, generalization ability and anti-interference, and it has improved the reconstructed image quality which has an average reduction of 55.09% and 26.23% on RE (Relative Error) and an increase of 14.19% and 3.08% on CC (Correlation Coefficient) respectively compared with RBF-EIT and RBF-UNet methods. In addition, the experimental data from KIT4 system can be applied to the trained network. This successful transition also demonstrates the proposed method can reconstruct more explicit images with high fidelity.

Use of geophysical methods to evaluate soil sediments behind gabion check dams in the dry regions of southern Tunisia.

This study aims to detect sediment at six gabions check-dams distributed in the upstream and downstream areas of the Koutine catchment located in an arid area in the southeast of Tunisia and characterized by an annual mean precipitation of less than 200 mm. The detection of sediment is based on the Electrical Resistivity Tomography (ERT) method associated with topographic measurements. About ten lines were arranged, with 72 electrodes. The results of resistivity data obtained during field measurements were inverted into subsurface structures using least squares inversion techniques. The preliminary results indicate that the sediment can be identified using an ERT contour method. The obtained results are calibrated based on samples collected for laboratory analysis. The accuracy of the high-density ERT method was justified. The density increases with the sediment deposit depth. Topographic methods were used to estimate the surface and the relief of deposed sediments in the area monitored by the gabions check-dams. This study provides an approach based on the high-density electrical resistivity tomography method and a topographic investigation to estimate sediment yield behind gabion check-dams that control catchments. The sedimentary deposit of eroded soils reduces the effectiveness of the recharge structures. Consequently, the improvement of permeability at the level of the retention basins (by cleaning the settlement basin and creating recharge wells) is of great importance. The study results are beneficial for decision-makers to evaluate the existing soil conservation and water management plans, which can be further adjusted using appropriate soil erosion mitigation options based on scientific evidence.

New application of saline contrast-enhanced electrical impedance tomography method for right ventriculography besides lung perfusion: detection of right-to-left intracardiac shunt.

Saline contrast-enhanced electrical impedance tomography (EIT) has been used to identify the respiratory failure etiologies through assessment of regional lung perfusion at the bedside. In this study, we introduce a novel approach to detect right-to-left intracardiac shunt based on the center of heart (CoH) parameter determined from the early phase of impedance-time curve after saline bolus injection. The timepoints when the saline bolus enters the heart (T0) and the lung regions (T1) are identified at first. A moving time window from T0 to T1 is then generated with steps of 0.5 s and the slope of the impedance-time curve in each pixel within the window calculated. CoH is calculated as the geometric center of pixel slope values in the right-to-left image direction. To illustrate how this method works in practice, we calculated the CoH values at T0 to T1 in 10 control hypoxic patients with no right-to-left shunt. In addition, we examined two critically ill patients with right-to-left intracardiac shunt. one was postcardiac surgery patient who had a residual atrial septal defect by color doppler of transesophageal echocardiograph. The other patient had a congenital heart disease of ventricular septal defect by color doppler of trans-thoracic echocardiography. A large difference in CoH between T0 to T1 was observed in the two patients with intracardiac shunt than in the control patients (11.06 ± 3.17% vs. 1.99 ± 1.43%, P = 0.030). saline bolus EIT for lung perfusion might be used as ventriculography to identify the right-to-left intracardiac shunt at the bedside.

Soil resistivity measurements to evaluate subsoil salinity in rice production systems in the Vietnam Mekong Delta

AbstractRice is a staple crop in the Vietnam Mekong Delta (VMD) in which more than half of Vietnam's rice is produced. However, rice production in the VMD is threatened by increasing saltwater intrusion due to land subsidence and climate change induced sea level rise. Saltwater intrusion into lowland areas through the canal system or capillary rise of saline water from near surface saline water tables may result in salt accumulation in the topsoil. Therefore, it is important to disentangle the two effects and their relative importance to implement appropriate strategies for water and salinity management for adapting rice production systems of the VMD to climate change. Here, we report on the possibility of using geoelectrical methods to evaluate the potential threat of subsoil salinity to rice production. To evaluate the level of subsoil salinity, we measured soil electrical resistivity using an ARES II to a depth of 40 m in a case study comprising five locations in the VMD. Electrical resistivity measurements were calibrated to soil types, which were identified through evaluating 1 m core sections obtained by drilling down to 40 m depth. The relationship between drilling data and soil resistivity was determined by applying clustering and principal component analysis. Resistivity values smaller than 3 Ω m were clearly identified as indicative for a saline water table. The results show a direct link between the depth of the saline water table and the proximity to the sea, but not to the rice production system (single, double, or triple cropping). This study proved for the first time the applicability of the electrical resistivity tomography method for identifying groundwater tables and evaluating subsoil salinity on an agricultural field scale in the VMD.

Combination of 2D-Electrical Resistivity Imaging and Seismic Refraction Tomography methods for groundwater potential assessments: A case study of Khammouane province, Laos

2D Electrical Resistivity Imaging (2D-ERI) and Seismic Refraction Tomography (SRT) are non-destructive techniques widely used for numerous geophysical investigations, namely, structural geology mapping, archaeological, engineering, and groundwater investigations. The present study aims to define potential groundwater zones in the Thakhek district of Khammouane Province, Laos, by 2D-ERI and SRT methods; due to the limitation of groundwater potential information, monitoring and evaluation activities regarding groundwater quantity and quality have not been conducted in this study area. The 2D-ERI measurement is based on the Wenner configuration with an electrode spacing of 10-160 m. In contrast, SRT uses a 6.5 kg sledgehammer for a seismic source with a 4 m geophone interval. The results indicate moderate resistivity values ranging from 18.8-71 Ohm-m, and seismic velocities ranging from 1220-2140 m/s were found at 12-30 m in the study region, illustrating the existence of a groundwater/aquifer at this depth. These results correlate well with drilling results from the borehole measurements in the Thakhek district, where the water levels were found at a depth of 12 m for borehole 1 and 15 m for borehole 2. The present study also demonstrates the correlation between 2D-ERI and SRT techniques. The adopted methods favor groundwater identification in the study region and other areas with similar geology formations.

Recognition of the flysch substrate using the electrical resistivity tomography (ERT) method to assess the effectiveness of the injection process

During the construction of a section of the S-7 Lubień – Rabka-Zdrój dual expressway, located in the area of the Carpathian flysch (Carpathian Flysch Belt, South Poland), damage to the embankment was observed, as well as cracks and depressions in the new pavement. An analysis of the geological and engineering conditions in the area of the road section under construction showed the existence of a complex tectonic structure of the flysch formations, a shallow groundwater table, and numerous landslides. In order to stabilize the road substrate, it was decided to carry out injections, and the locations of these injections were initially geotechnically tested. However, due to the high variability of the geological structure, the target method employed was electrical resistivity tomography (ERT), which performed the survey in two stages. In Stage I, the geoelectrical/geochemical structure of the near-surface zone was identified, and the probable causes of road damage were indicated. This stage was completed by performing the stabilization and sealing process of the ground with an injection mixture. In Stage II, studies were carried out to evaluate the effectiveness of the injection process. The ERT method effectively identified the shallow geological structure and, in particular, delineated the zone of strong fractures in the flysch and areas associated with faults. Using the electrical resistivity tomography method, it was also possible to determine the injection mixture’s approximate penetration depth and the loosening zone’s degree of filling.

Detection of Landfill Leachate Leakage Based on ERT and OCTEM

Leakage in the impervious layer of a domestic waste landfill seriously pollutes the soil and groundwater. Therefore, it is necessary to carry out rapid nondestructive leakage location detection. In this research, the electrical resistivity tomography (ERT) method and the opposing-coils transient electromagnetic method (OCTEM) were used to detect the leakage location. The inversion sections of both methods showed a clear low–middle–high resistivity spectrum in the longitudinal direction that could be used to speculate the distribution pattern of the upper waste body layer, the bottom impermeable layer, and the lower limestone layer. The leakage area was identified in Zone B of the landfill on the basis of inversion results and drilling verification results. The results indicate that OCTEM and ERT were both sensitive to leakage detection. However, OCTEM had higher longitudinal resolution and more refined inversion results, resulting in more effective delineation for the location of the damage and leakage of the impervious landfill layer, thereby providing a new technical basis for landfill leakage detection.

A review of Python-based code for landslide modeling and inversion using Electrical Resistivity Tomography method

A review of Python-based code for landslide modeling and inversion using Electrical Resistivity Tomography method

Geological Factor Causing Water Decrease of the Baturagung Reservoir, Based on ERT Geoelectric Application

The Baturagung reservoir, a small artificial lake is located in the Gedangrejo village, Karangmojo district, Gunungkidul regency, Yogyakarta Special Region, Indonesia. Initially, the reservoir was built on hilly geomorphology with volcanic sandstone lithology intended to meet the agricultural water needs of the people in the surrounding area, and as a tourist spot as well. Since 2019, there has been a decrease in the volume of reservoir water so that the reservoir is never fully filled with water. Due to the decrease in reservoir water volume, residents' water needs are not being met, and visitors to this place are reduced. Therefore, it is important to accomplish a study with the purpose to identify the factors that cause reservoir water depletion, such as the conditions of geomorphology, lithological variations, geological structures, and hydrogeology of the area. The methodologies used in this study are field surveys, surface mapping, and the application of the electric resistivity tomography method. The results show that there is a weak zone with a resistivity ranges 4.24– 45.9 Ωm, northeast-southwest trend, interpreted as a fault crossing the study area. It is deduced that the fault is active, causing the tearing of the geomembrane underlying the reservoir, initiating water leakage from the reservoir to the southwest direction.

Monitoring Methodology Study of a Reservoir Built on the Karst Depression: A Large Scale Laboratory Simulation Test.

The karst depression with a natural negative landform is favorable for reservoir construction with less excavation work. The underground air-water pressure would be complicated after the construction of a reservoir that blocks the natural air-water channel (sinkhole, karst channel, etc.). To develop a monitoring system for the reservoir, a large-scale laboratory simulation test was carried out to study the air-pressure evolution and water migration process during water table fluctuation after the blockage of the sinkhole in a karst depression. The results are as follows. (1) The positive pressure jacking effect and the negative pressure sucking effect were observed in the karst channel and inside the model during groundwater table fluctuation. (2) A water imbibition test on the rock-like material was carried out with layered resistivity and layered NMR measurement. The relationship of resistivity and water saturation was developed based on Archie's equation. (3) The resistivity evolution during the test was monitored using the high-density electronic resistivity imaging method. The resistivity of the measured profile was sensitive to the variation of the water level, and the water migration process was quantified by the resistivity to water saturation conversion. (4) The suitability of many techniques for monitoring a reservoir built on the karst depression was discussed. The resistivity monitoring technique combined with the air-water pressure monitoring technique could provide useful information for safety and reliability assessment.

Reconstruction of conductivity distribution variation with Tikhonov and wavelet frame combined method for electrical impedance tomography

Electrical impedance tomography (EIT) is receiving considerable research interest in a variety of applications. With this technique, it is possible to reconstruct conductivity distribution inside the detected region. Note that reconstruction of conductivity distribution is an ill-posed inverse problem. To deal with this problem, Tikhonov regularization method has been preferred. However, this method suffers from poor reconstruction quality. In this work, a novel approach which combines Tikhonov regularization method with wavelet frame is proposed for image reconstruction of EIT. The proposed method is superior to the popular Tikhonov regularization method in enforcing sparse of the solution and enhancing sharp feature. Simulation work has been conducted to validate the performance of the proposed method. Compared with Landweber method, total variation (TV) regularization method, and Tikhonov regularization method, reconstructions of six different models show that images reconstructed by the proposed method have better quality and are more robust to noise. In addition, image reconstruction is also performed based on phantom experimental data. The results further demonstrate that the proposed method outperforms other three methods since the inclusion has been more accurately reconstructed, and there are almost no artifacts in the reconstructed images.

Approbation of seismic and electrical geophysical techniques complex for solving the permafrost monitoring problems on the pile-foundation building

In the urban conditions in Salekhard city, a complex of methods, including electrical resistivity tomography (ERT), ground penetrating radar (GPR), a seismic survey on refracted waves (REF), on surface waves (MASW) and the standing waves selection, was tested on solving geocryological problems and monitor the permafrost at the building base. As a model object, a residential building on a pile foundation, built according to the principle I and equipped with a continuous geothermal monitoring system, was chosen. It has been established that the ERT, REF, and MASW methods are ineffective in the conditions of a reinforced concrete pile foundation in a grillage and a concrete floor screed with a layer of loose bulk soil under it. The best result was shown by GPR at frequencies of 150 and 400 MHz and seismic exploration with the standing wave selection. A combination of these methods is recommended for determining the upper permafrost boundary under buildings, determining the actual piles-length, the quality of their fixing, assessing the water content of soils in the area around the piles, and establishing the residual building life.