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.

Decennial multi-approach monitoring of thermo-hydro-mechanical processes, Kammstollen outdoor laboratory, Zugspitze (Germany)

2021 ◽  
Author(s):  
Riccardo Scandroglio ◽  
Till Rehm ◽  
Jonas K. Limbrock ◽  
Andreas Kemna ◽  
Markus Heinze ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Environmental Research ◽  
Permafrost Degradation ◽  
Earth Surface ◽  
Data Set ◽  
Resistivity Tomography ◽  
Near Surface ◽  
Permafrost Rock ◽  
Austrian Alps

<p>The warming of alpine bedrock permafrost in the last three decades and consequent reduction of frozen areas has been well documented. Its consequences like slope stability reduction put humans and infrastructures at high risk. 2020 in particular was the warmest year on record at 3000m a.s.l. embedded in the warmest decade.</p><p>Recently, the development of electrical resistivity tomography (ERT) as standard technique for quantitative permafrost investigation allows extended monitoring of this hazard even allowing including quantitative 4D monitoring strategies (Scandroglio et al., in review). Nevertheless thermo-hydro-mechanical dynamics of steep bedrock slopes cannot be totally explained by a single measurement technique and therefore multi-approach setups are necessary in the field to record external forcing and improve the deciphering of internal responses.</p><p>The Zugspitze Kammstollen is a 850m long tunnel located between 2660 and 2780m a.s.l., a few decameters under the mountain ridge. First ERT monitoring was conducted in 2007 (Krautblatter et al., 2010) and has been followed by more than one decade of intensive field work. This has led to the collection of a unique multi-approach data set of still unpublished data. Continuous logging of environmental parameters such as rock/air temperatures and water infiltration through joints as well as a dedicated thermal model (Schröder and Krautblatter, in review) provide important additional knowledge on bedrock internal dynamics. Summer ERT and seismic refraction tomography surveys with manual and automated joints’ displacement measurements on the ridge offer information on external controls, complemented by three weather stations and a 44m long borehole within 1km from the tunnel.</p><p>Year-round access to the area enables uninterrupted monitoring and maintenance of instruments for reliable data collection. “Precisely controlled natural conditions”, restricted access for researchers only and logistical support by Environmental Research Station Schneefernerhaus, make this tunnel particularly attractive for developing benchmark experiments. Some examples are the design of induced polarization monitoring, the analysis of tunnel spring water for isotopes investigation, and the multi-annual mass monitoring by means of relative gravimetry.</p><p>Here, we present the recently modernized layout of the outdoor laboratory with the latest monitoring results, opening a discussion on further possible approaches of this extensive multi-approach data set, aiming at understanding not only permafrost thermal evolution but also the connected thermo-hydro-mechanical processes.</p><p> </p><p> </p><p>Krautblatter, M. et al. (2010) ‘Temperature-calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps)’, Journal of Geophysical Research: Earth Surface, 115(2), pp. 1–15. doi: 10.1029/2008JF001209.</p><p>Scandroglio, R. et al. (in review) ‘4D-Quantification of alpine permafrost degradation in steep rock walls using a laboratory-calibrated ERT approach (in review)’, Near Surface Geophysics.</p><p>Schröder, T. and Krautblatter, M. (in review) ‘A high-resolution multi-phase thermo-geophysical model to verify long-term electrical resistivity tomography monitoring in alpine permafrost rock walls (Zugspitze, German/Austrian Alps) (submitted)’, Earth Surface Processes and Landforms.</p>

Target-oriented optimized survey design and quantitative comparison for 3D electrical resistivity tomography

2020 ◽  
Author(s):  
Lincheng Jiang ◽  
Gang Tian ◽  
Bangbing Wang ◽  
Amr Abd El-Raouf
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Survey Design ◽  
Quantitative Comparison ◽  
Data Set ◽  
Resistivity Tomography ◽  
Near Surface ◽  
Target Set ◽  
Survey Designs

<p>In recent decades, geoelectrical methods have played a very important role in near-surface investigation. The most widely used of these methods is electrical resistivity tomography (ERT). Regardless of the forward and inversion algorithms used, the original data collected from a survey is the most important factor for quality of the resulted model. However, 3D electrical resistivity survey design continues to be based on data sets recorded using one or more of the standard electrode arrays. There is a recognized need for the 3D survey design to get better resolution using fewer data. Choosing suitable data from the comprehensive data set is a great approach. By reasonable selecting, better resolution can be obtained with fewer electrodes and measurements than conventional arrays. Previous research has demonstrated that the optimized survey design using the 'Compare R' method can give a nice performance.</p><p>This paper adds target-oriented selection and modified the original 'Compare R' method. The survey design should be focused on specific target areas, which need a priori information about the subsurface properties. We select electrodes and configurations as the target set by the comprehensive set firstly which meets the requirements of the target area. The number of measurements and electrodes is much less than the comprehensive set and the model resolution matrix takes less time to calculate. At the next step for rank, we calculate the sensitivity matrix of the target set only once and then calculate the contribution degree of each measurement separately from it. The time of iterative calculation of the resolution matrix when measurements set changing is less than the original method.</p><p>The traditional method of evaluating RMS is not appropriate for comparing the quality of collected data by different survey designs. SSIM (structural similarity index) gives more reliable measures of image similarity better than the RMS. The curves of SSIM values in three dimensions and the average SSIM are given as quantitative comparisons. Besides, the frequency of electrodes utilized given to guides on selecting the highest used electrodes. Finally, the curves of the average relative resolution S and the number of electrodes as the number of measurements increase are given, which proves the method works effectively.</p><p>The results show the significance of using target-oriented optimized survey design, as it selects fewer electrodes and arrays than the original CR method. Also, it produces better resolution than conventional arrays and takes less calculation time. 3D SSIM, frequency of electrodes used, the relationship between average relative resolution, number of electrodes and number of measurements, these quantitative comparison methods can effectively evaluate the data collected in various survey designs.</p>

scholarly journals Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites

2018 ◽  
Author(s):  
Coline Mollaret ◽  
Christin Hilbich ◽  
Cécile Pellet ◽  
Adrian Flores-Orozco ◽  
Reynald Delaloye ◽  
...  
Keyword(s):  
Time Series ◽  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Permafrost Degradation ◽  
Data Set ◽  
Resistivity Tomography ◽  
Wide Range ◽  
Mountain Permafrost ◽  
Ice Water

Abstract. Mountain permafrost is sensitive to climate change and is expected to gradually degrade in response to the ongoing atmospheric warming trend. Long-term monitoring the permafrost thermal state is a key task, but it is problematic where temperatures are close to 0 °C. The energy exchange is indeed often dominantly related to latent heat effects associated with phase change (ice/water), rather than ground warming or cooling. Consequently, it is difficult to detect significant spatio-temporal variations of ground properties (e.g. ice-water ratio) that occur during the freezing/thawing process with point scale temperature monitoring alone. Hence, electrical methods have become popular in permafrost investigations as the resistivities of ice and water differ by several orders of magnitude, theoretically allowing a clear distinction between frozen and unfrozen ground. In this study we present an assessment of mountain permafrost evolution using long-term electrical resistivity tomography monitoring (ERTM) from a network of permanent sites in the Central Alps. The time series consist of more than 1000 data sets from six sites, where resistivities have been measured on a regular basis for up to twenty years. We identify systematic sources of error and apply automatic filtering procedures during data processing. In order to constrain the interpretation of the results, we analyse inversion results and long-term resistivity changes in comparison with existing borehole temperature time series. Our results show that the resistivity data set provides the most valuable insights at the melting point. A prominent permafrost degradation trend is evident for the longest time series (19 years), but also detectable for shorter time series (about a decade) at most sites. In spite of the wide range of morphological, climatological and geological differences between the sites, the observed inter-annual resistivity changes and long-term tendencies are similar for all sites of the network.

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 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 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.

Numerical and experimental mapping of small root zones using optimized surface and borehole resistivity tomography

Geophysics ◽  
2011 ◽  
Vol 76 (2) ◽  
pp. G25-G35 ◽  
Author(s):  
Said Attia al Hagrey ◽  
Torsten Petersen
Keyword(s):  
Small Data ◽  
Optimization Approach ◽  
Electrode Arrays ◽  
Spatiotemporal Resolution ◽  
Data Set ◽  
Resistivity Tomography ◽  
Root Zones ◽  
Small Root ◽  
Input Model ◽  
Surface Borehole

An exact mapping of root zones is essential to understand plant growth, root biomass, and soil functions important for environmental and climatic management and protection. Numerical and experimental techniques of the electrical resistivity tomography were applied in 2D and 3D to resolve small root zones in the centimeter range. Numerically, we studied two scenarios of conductive and resistive root zones as a function of (1) eight different quadripole electrode configurations (standard, nonstandard, and optimized), (2) four different survey designs with electrode arrays at the soil surface and in boreholes, and (3) eight different inversion constraints. The best resolved output tomogram was evaluated semiquantitatively using the criteria of visual similarity to the input model, least data set, rms error, and iteration number and quantitatively by the model difference relative to the input model. The results showed that the surface-borehole configurations have the best resolution for the whole root zone. The single-surface and borehole surveys resolve only the respective upper and middle-lower root parts. The results reflect the potential of the optimization approach to generate small data sets of far higher resolution than the standard sets. Based on these results, we used the surface-borehole survey around a young hibiscus planted in a sandy soil in a laboratory experiment. The surface-borehole surveys using small, optimized configurations result in an optimum spatiotemporal resolution for simultaneous applications for 3D mapping of targets (root zones and water and soil heterogeneities) and 4D monitoring of their processes.

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