scholarly journals Archaeological investigations in the shallow seawater environment with electrical resistivity tomography

2021 ◽  
Author(s):  
Kleanthis Simyrdanis ◽  
Nikos Papadopoulos ◽  
Jung-Ho Kim ◽  
Panagiotis Tsourlos ◽  
Ian Moffat
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
A Priori ◽  
Simulation Models ◽  
Burial Depth ◽  
Electrode Arrays ◽  
Resistivity Tomography ◽  
Priori Information ◽  
Target Characteristics ◽  
Special Environment

This work explores the applicability and effectiveness of electrical resistivity tomography in mapping archaeological relics in the shallow marine environment. The approach consists of a methodology based on numerical simulation models validated with comparison to field data. Numerical modelling includes the testing of different electrode arrays suitable for multi-channel resistivity instruments (dipole–dipole, pole–dipole, and gradient). The electrodes are placed at fixed positions either floating on the sea surface or submerged at the bottom of the sea. Additional tests are made concerning the resolving capabilities of electrical resistivity tomography with various seawater depths and target characteristics (dimensions and burial depth of the targets). Although valid a priori information, in terms of water resistivity and thickness, can be useful for constraining the inversion, it should be used judiciously to prevent erroneous information leading to misleading results. Finally, an application of the method at a field site is presented not only for verifying the theoretical results but also at the same time for proposing techniques to overcome problems that can occur due to the special environment. Numerical and field electrical resistivity tomography results indicated the utility of the method in reconstructing off-shore cultural features, demonstrating at the same time its applicability to be integrated in wider archaeological projects.

scholarly journals Development of an Electrical Resistivity Tomography Monitoring Concept for the Svelvik CO<sub>2</sub> Field Lab, Norway

2020 ◽  
Vol 54 ◽  
pp. 41-53
Author(s):  
Tobias Raab ◽  
Wolfgang Weinzierl ◽  
Bernd Wiese ◽  
Dennis Rippe ◽  
Cornelia Schmidt-Hattenberger
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Co2 Storage ◽  
Pressure Effects ◽  
Co2 Injection ◽  
Target Area ◽  
Electrode Arrays ◽  
Resistivity Tomography ◽  
Monitoring Well ◽  
Co2 Plume

Abstract. Within the ERA-NET co-funded ACT project Pre-ACT (Pressure control and conformance management for safe and efficient CO2 storage – Accelerating CCS Technologies), a monitoring concept was established to distinguish between CO2 induced saturation and pore pressure effects. As part of this monitoring concept, geoelectrical cross-hole surveys have been designed and conducted at the Svelvik CO2 Field Lab, located on the Svelvik ridge at the outlet of the Drammensfjord in Norway. The Svelvik CO2 Field Lab has been established in summer 2019, and comprises four newly drilled, 100 m deep monitoring wells, surrounding an existing well used for water and CO2 injection. Each monitoring well was equipped with modern sensing systems including five types of fiber-optic cables, conventional- and capillary pressure monitoring systems, as well as electrode arrays for Electrical Resistivity Tomography (ERT) surveys. With a total of 64 electrodes (16 each per monitoring well), a large number of measurement configurations for the ERT imaging is possible, requiring the performance of the tomography to be investigated beforehand by numerical studies. We combine the free and open-source geophysical modeling library pyGIMLi with Eclipse reservoir modeling to simulate the expected behavior of all cross-well electrode configurations during the CO2 injection experiment. Simulated CO2 saturations are converted to changes in electrical resistivity using Archie's Law. Using a finely meshed resistivity model, we simulate the response of all possible measurement configurations, where always two electrodes are located in two corresponding wells. We select suitable sets of configurations based on different criteria, i.e. the ratio between the measured change in apparent resistivity in relation to the geometric factor and the maximum sensitivity in the target area. The individually selected measurement configurations are tested by inverting the synthetic ERT data on a second coarser mesh. The pre-experimental, numerical results show adequate resolution of the CO2 plume. Since less CO2 was injected during the field experiment than originally modeled, we perform post-experimental tests of the selected configurations for their potential to image the CO2 plume using revised reservoir models and injection volumes. These tests show that detecting the small amount of injected CO2 will likely not be feasible.

scholarly journals Computation of Optimized Electrode Arrays for 3-D Electrical Resistivity Tomography Surveys

2021 ◽  
Vol 11 (14) ◽  
pp. 6394
Author(s):  
Kleanthis Simyrdanis ◽  
Nikos Papadopoulos ◽  
Dimitrios Oikonomou
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Jacobian Matrix ◽  
Optimization Technique ◽  
Optimization Approach ◽  
Electrode Arrays ◽  
Data Set ◽  
Resistivity Tomography ◽  
Parallel Lines ◽  
Comprehensive Data

The present study explores the applicability and effectiveness of an optimization technique applied to electrical resistivity tomography data. The procedure is based on the Jacobian matrix, where the most sensitive measurements are selected from a comprehensive data set to enhance the least resolvable parameters of the reconstructed model. Two existing inversion programs in two and three dimensions are modified to incorporate this new approach. Both of them are selecting the optimum data from an initial comprehensive data set which is comprised of merged conventional arrays. With the two-dimensional (2-D) optimization approach, the most sensitive measurements are selected from a 2-D survey profile and then a clone of the resulting optimum profile reproduces a three-dimensional (3-D) optimum data set composed of equally spaced parallel lines. In a different approach, with the 3-D optimization technique, the optimum data are selected from a 3-D data set of equally spaced individual parallel lines. Both approaches are compared with Stummer’s optimization technique which is based on the resolution matrix. The Jacobian optimization approach has the advantage of selecting the optimum data set without the need for the solution of the inversion problem since the Jacobian matrix is calculated as part of the forward resistivity problem, thus being faster from previous published approached based on the calculation of the sensitivity matrix. Synthetic 3-D data based on the extension of previous published works for the 2-D optimization case and field data from two case studies in Greece are tested, thus verifying the validity of the present study, where fewer measurements from the initial data set (about 15–50%) are able to reconstruct a model similar with the one produced from the original comprehensive data set.

scholarly journals COMPARISON OF THE GEOELECTRIC SIGNATURE WITH DIFFERENT ELECTRODE ARRAYS AT THE JOCKEY CLUB LANDFILL OF BRASÍLIA, DF, BRAZIL

2020 ◽  
Vol 38 (1) ◽  
pp. 41
Author(s):  
Victor José Cavalcanti Bezerra Guedes ◽  
Victória Basileu de Oliveira Lima ◽  
Welitom Rodrigues Borges ◽  
Luciano Soares da Cunha
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Inversion Method ◽  
Electrode Arrays ◽  
L1 Norm ◽  
Resistivity Tomography ◽  
L2 Norm ◽  
Data Resolution ◽  
Multichannel Data ◽  
Jockey Club

ABSTRACT. The influence of array configurations on the resolution of subsurface electrical resistivity tomography (ERT) imaging is one of the most discussed factors when it comes to resistivity data quality. Despite the flexibility of multichannel data acquisition systems nowadays, there is still a tendency to perform field observations with traditional arrays, mainly because they are already well understood configurations. The present work discusses a comparison between the results obtained with four electrode arrays (dipole dipole, pole-dipole, Wenner-Schlumberger and Wenner) regarding the data resolution and the ability to identify the bedrock over the buried waste in the former Jockey Club landfill of Brasília, an important information to delimit the geometry of the mass of waste. Four electroresistivity lines were acquired with different electrode arrays, using the ERT technique, and models were calculated using the Res2DInv software, by the robust inversion method (L1-norm) and smooth-constrained least squares inversion (L2-norm). All arrangements produced models that presented the mass of waste with low resistivity, indicating strong influence of leachate. The best agreement with borehole information regarding the bedrock level was achieved with the dipole-dipole array. The L1-norm inversion provided more stable and smoothed models than the results obtained with the L2-norm method, also presenting smaller differences between the calculated and observed apparent resistivity.KEYWORDS: Electrical Resistivity Tomography, electrode arrays, waste disposal. COMPARAÇÃO DA ASSINATURA GEOELÉTRICA COM DIFERENTES ARRANJOS ELETRÓDICOS NO ATERRO JOCKEY CLUBE DE BRASÍLIA, DF, BRASILRESUMO. A influência do arranjo eletródico na resolução de imageamento por tomografia de resistividade elétrica (TRE) da subsuperfície é um dos fatores mais discutidos quando se trata de qualidade de dados de resistividade. Apesar da flexibilidade dos sistemas multicanais de aquisição de dados, ainda há uma tendência em realizar observações em campo com arranjos tradicionais de eletrodos, devido a serem configurações já bem compreendidas. No presente trabalho, é discutida uma comparação entre os resultados obtidos a partir de quatro arranjos de eletrodos (dipolo-dipolo, polo-dipolo, Wenner-Schlumberger e Wenner) quanto a resolução dos dados e quanto a capacidade de identificar o embasamento rochoso sobre o maciço de resíduos no antigo aterro controlado do Jockey Clube de Brasília, uma importante informação para delimitar a geometria do maciço de resíduos. Foram adquiridas quatro linhas de eletrorresistividade com diferentes arranjos eletródicos, com a técnica TRE, e foram calculados modelos no software Res2DInv pelo método de inversão robusta (norma-L1) e de inversão de mínimos quadrados com restrição de suavidade (norma-L2). Todos os arranjos produziram modelos que apresentaram o maciço de resíduos com baixa resistividade, indicando forte influência de chorume. As melhores concordâncias com as informações de furos de sondagem foram alcançadas com o arranjo dipolo-dipolo. A inversão norma-L1 forneceu modelos mais estáveis e suavizados do que os resultados obtidos com a norma-L2, também apresentando diferenças menores entre a resistividade aparente calculada e medida.PALAVRAS-CHAVE: Tomografia de Resistividade Elétrica, arranjos eletródicos, disposição de resíduos.

scholarly journals Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging

2020 ◽  
Vol 28 (6) ◽  
pp. 2115-2127
Author(s):  
M. L. Rockhold ◽  
J. L. Robinson ◽  
K. Parajuli ◽  
X. Song ◽  
Z. F. Zhang ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Industrial Waste ◽  
Electrical Resistivity Tomography ◽  
Groundwater Extraction ◽  
Waste Site ◽  
Electrode Arrays ◽  
Deep Subsurface ◽  
Resistivity Tomography ◽  
Perched Water ◽  
Perched Aquifer

Abstract A contaminated industrial waste site in Washington State (USA) containing buried, metallic-waste storage tanks, pipes, and wells, was evaluated to determine the feasibility of monitoring groundwater remediation activities associated with an underlying perched aquifer system using electrical resistivity tomography. The perched aquifer, located ~65 m below ground surface and ~10 m above the regional water table, contains high concentrations of nitrate, uranium, and other contaminants of concern from past tank leaks and intentional releases of wastes to surface disposal sites. The extent of the perched water aquifer is not well known, and the effectiveness of groundwater extraction for contaminant removal is uncertain, so supplemental characterization and monitoring technologies are being evaluated. Numerical simulations of subsurface flow and contaminant transport were performed with a highly resolved model of the hydrogeologic system and waste site infrastructure, and these simulations were used as the physical basis for electrical resistivity tomography modeling. The modeling explicitly accounted for metallic infrastructure at the site. The effectiveness of using surface electrodes versus surface and horizontal subsurface electrodes, for imaging groundwater extraction from the perched water aquifer, was investigated. Although directional drilling is a mature technology, its use for electrode emplacement in the deep subsurface under a complex industrial waste site via horizontal wells has not yet been demonstrated. Results from this study indicate that using horizontal subsurface electrode arrays could significantly improve the ability of electrical resistivity tomography to image deep subsurface features and monitor remediation activities under complex industrial waste sites.

scholarly journals Determination of dipping contacts using electrical resistivity tomography

2012 ◽  
Vol 42 (2) ◽  
pp. 161-180
Author(s):  
René Putiška ◽  
Ivan Dostál ◽  
David Kušnirák
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Image Resolution ◽  
High Resistivity ◽  
Depth Range ◽  
Electrode Arrays ◽  
Resistivity Tomography ◽  
Imaging Geometry ◽  
Lithostratigraphic Units

Determination of dipping contacts using electrical resistivity tomographyGenerally, all electrode arrays are able to delineate the contact of two lithostratigraphic units especially with very high resistivity contrast. However, the image resolution for the location of vertical and dipping structures is different. The responses of dipole-dipole (DD), Wenner alpha (WA), Schlumberger (SCH) and combined pole-dipole (PD) arrays have been computed using the finite difference method. Comparison of the responses indicates that: (1) The dipole-dipole array usually gives the best resolution and is the most detailed method especially for the detection of vertical structures. This array has shown the best resolution to recognize the geometrical characterisation of the fault. (2) The pole-dipole has shown the second best result in our test. The PD is an effective method for detection of vertical structures with a high depth range, but the deepest parts are deformed. (3) Wenner alpha shows a low resolution, inconvenient for detailed investigation of dip structures. (4) The Schlumberger array gives a good and sharp resolution to assess the contact between two lithological units but gives poor result for imaging geometry of dipping contact.

scholarly journals Solution of Collinearity Problem in Two-Dimensional Electrical Resistivity Tomography using Wenner Array

2021 ◽  
Vol 29 (2) ◽  
Author(s):  
Mustapha Adejo Mohammed ◽  
Nordiana Mohd Muztaza ◽  
Rosli Saad
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Two Dimensional ◽  
Electrode Arrays ◽  
Resistivity Tomography ◽  
Underlying Assumption ◽  
New Approach ◽  
Surface Constraint ◽  
True Model ◽  
Wenner Array

Two-dimensional electrical resistivity tomography (2-D ERT) is one of the most common geophysical tools employed to satisfy the ever-growing need for obtaining subsurface information. Most of the conventional electrode arrays used for 2-D ERT survey are built with the theoretical assumption that the survey lines are straight to guarantee four collinear electrodes at every point of measurement. However, due to surface constraint associated with most survey areas, it is rarely possible to conduct a two-dimensional resistivity survey on a straight line. Therefore, 2-D ERT survey conducted on a surface constraint field requires shifting one or more electrodes off the survey line, which contrasts with the underlying assumption. Consequently, the result might be prone to false anomalies. Thus, this study aimed to device a new approach that could mitigate the false anomalies posed by non-collinearity of electrodes in 2-D ERT result. In view of this, ABEM Terrameter SAS4000 using Wenner array configuration was adopted for the survey. The data was acquired with all electrodes inline and one or more electrodes offline at stepwise distances, respectively. Based on the result obtained, the new approach mitigates the offline electrodes effect, as the inverse resistivity tomograms resolves the geometries of the true model reasonably well. More so, it has high R-value >90% which is an indication of proximity to the true model. Hence, it is concluded that the new approach is effective in mitigating offline electrode effect on a 2-D ERT result.

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