Constraining electric resistivity tomography by direct push electric conductivity logs and vibracores: An exemplary study of the Fiume Morto silted riverbed (Ostia Antica, western Italy)

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. B87-B103 ◽  
Author(s):  
Tina Wunderlich ◽  
Peter Fischer ◽  
Dennis Wilken ◽  
Hanna Hadler ◽  
Ercan Erkul ◽  
...  
Keyword(s):  
A Priori ◽  
Electric Resistivity ◽  
Structural Constraints ◽  
Resistivity Tomography ◽  
Subsurface Structures ◽  
Direct Push ◽  
Ostia Antica ◽  
High Vertical Resolution ◽  
Ground Truthing ◽  
Priori Information

The inversion of geoelectric data is nonunique. Therefore, electric resistivity tomography (ERT) usually results in different subsurface models that fit observed apparent resistivity values equally well. To reduce the uncertainty, constraints on the geometry and resistivity of subsurface structures can be incorporated into the ERT inversion. We test different ways of constraining ERT by applying (1) improved starting models, (2) structural constraints, and (3) structural and resistivity constraints. A priori information is needed for these approaches, which is acquired from direct push electrical conductivity (DP-EC) logs and vibracores in our study. We found that adapting high vertical resolution of DP-EC logs to coarser ERT resolution requires blocking of the logs. These blocked logs can be used for constraining the ERT inversion with resistivity and structural constraints along so-called regions around the log locations, which was found to be the best approach. In this case, ground truthing with additional DP-EC logs that were not used for constraining showed the lowest root-mean-square error between logs and ERT model.

Inversion of inductive electromagnetic data in highly conductive terrains

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. G16-G28 ◽  
Author(s):  
G. Schultz ◽  
C. Ruppel
Keyword(s):  
A Priori ◽  
Two Dimensions ◽  
Forward Model ◽  
Practical Applications ◽  
Shallow Subsurface ◽  
Subsurface Structures ◽  
Conductivity Structure ◽  
Actual Field ◽  
Priori Information ◽  
The Stability

Despite the increasing use of controlled-source frequency-domain EM data to characterize shallow subsurface structures, relatively few inversion algorithms have been widely applied to data from real-world settings, particularly in high-conductivity terrains. In this study, we develop robust and convergent regularized, least-squares inversion algorithms based on both linear and nonlinear formulations of mutual dipole induction for the forward problem. A modified version of the discrepancy principle based on a priori information is implemented to select optimal smoothing parameters that simultaneously guarantee the stability and best-fit criteria. To investigate the problems of resolution and equivalence, we consider typical layered-earth models in one and two dimensions using both synthetic and observed data. Synthetic examples show that inversions based on the nonlinear forward model more accurately resolve subsurface structure, and that inversions based on the linear forward model tend to drastically underpredict high conductivities at depth. Inversions of actual field data from well-characterized sites (e.g., National Geotechnical Experimentation Site; sand-dominated coastal aquifer in the Georgia Bight) are used to test the applicability of the model to terrains with different characteristic conductivity structure. A comparison of our inversion results with existing cone-penetrometer and downhole-conductivity data from these field sites demonstrates the ability of the inversions to constrain conductivity variations in practical applications.

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 Large-scale ERT surveys for investigating shallow regolith properties and architecture

2018 ◽  
Author(s):  
Laurent Gourdol ◽  
Rémi Clément ◽  
Jérôme Juilleret ◽  
Laurent Pfister ◽  
Christophe Hissler
Keyword(s):  
Large Scale ◽  
Electrical Resistivity Tomography ◽  
Electrode Spacing ◽  
Resistivity Tomography ◽  
Shallow Subsurface ◽  
Subsurface Structures ◽  
Ill Posed ◽  
High Vertical Resolution ◽  
Small Electrode ◽  
Cost Efficient

Abstract. Within the Critical Zone, regolith plays a key role in the fundamental hydrological function of water collection, storage, mixing and release. Electrical Resistivity Tomography (ERT) is recognized as a remarkable tool for characterizing the geometry and properties of the regolith, overcoming limitations inherent to conventional borehole-based investigations. However, ERT measurements with a high vertical resolution remain restricted to shallow depths, essentially due to the requirement of small electrode spacing increments (ESI). Under these circumstances, the use of ERT measurements for large horizontal surveys remains cumbersome and time-consuming. Here we focus on the need to optimize the ESI parameter in order to adequately characterize the subsurface fabric. We use a set of synthetic three-layered soil–saprock/saprolite–bedrock models in combination with a field dataset. We demonstrate that oversized ESI can significantly affect our perception of shallow subsurface structures by missing important layers and increasing the ill-posed inverse problem effects. More precisely, we document how a thin surficial layer can influence inverted ERT results and cause a resistivity bias, both at the surface and at deeper horizons. To overcome this limitation, we propose adding interpolated levels of surficial apparent resistivity based on a limited number of ERT profiles with small ESI. We demonstrate that our protocol significantly improves the accuracy of ERT profiles based on large ESI. Our protocol is time and cost efficient – especially in the case of large-scale ERT surveys.

Enhancing the Resolving Ability of ERT for Imaging Saltwater Intrusion through Improvements in Inversion Methods: A Laboratory and Numerical Study

Geophysics ◽  
2021 ◽  
pp. 1-65
Author(s):  
Meredith Goebel ◽  
Rosemary Knight ◽  
Seogi Kang
Keyword(s):  
Saltwater Intrusion ◽  
Reference Model ◽  
Numerical Study ◽  
A Priori ◽  
Geophysical Methods ◽  
Resistivity Tomography ◽  
Porosity And Permeability ◽  
Priori Information ◽  
High Level

Mapping and monitoring of saltwater intrusion are critical to the sustainable management of groundwater in coastal aquifers around the world. Increasingly, geophysical methods, such as electrical resistivity tomography (ERT), have been used to address these needs. We identified methods for the inversion of ERT data that would most accurately map the location and geometry of an intrusion wedge. This was accomplished using both laboratory and synthetic experiments, with the classic representation of an intrusion wedge perpendicular to the coast. The laboratory experiments allowed us to collect ERT data on a saltwater intrusion wedge in an environment where we had supporting data that provided (1) the distribution of salinity within the tank with which to verify our inversion results, (2) the resistivity, porosity and permeability of the porous medium, and (3) the transform between resistivity and salinity. The synthetic experiments allowed to explore issues of specific interest related to the presence of lithologic heterogeneity at a field site: the role of lithologic heterogeneity in introducing complexity both the resistivity-salinity relationship and the geometry of the saltwater intrusion wedge. We found that using a reference model with a good approximation of the wedge to inform the inversion greatly improved the ability of the resulting resistivity profile to map the wedge. Where there was no, or limited lithologic heterogeneity, a parametric approach, which constrained the range of possible solutions by solving for a sharp interface between the saltwater and freshwater regions, was very effective at capturing the wedge location and geometry. Where there was lithologic heterogeneity, a hybrid between the parametric and informed inversion approaches was most effective, resolving the wedge with a high level of accuracy with little a priori information.

Evaluation of known-boundary and resistivity constraints for improving cross-borehole DC electrical resistivity imaging of discrete fractures

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. D115-D127 ◽  
Author(s):  
Judith Robinson ◽  
Timothy Johnson ◽  
Lee Slater
Keyword(s):  
Electrical Resistivity ◽  
Fracture Zone ◽  
A Priori ◽  
Tetrahedral Mesh ◽  
Zone Model ◽  
Structural Constraints ◽  
A Priori Information ◽  
Discrete Fractures ◽  
Discrete Fracture ◽  
Priori Information

There is a need to better characterize discrete fractures in contaminated hard rock aquifers to determine the fate of remediation injections away from boreholes and also to evaluate hydraulic fracturing performance. A synthetic cross-borehole electrical resistivity study was conducted assuming a discrete fracture model of an existing contaminated site with known fracture locations. Four boreholes and two discrete fracture zones, assumed to be the dominant electrical and hydraulically conductive pathways, were explicitly modeled within an unstructured tetrahedral mesh. We first evaluated different regularization constraints starting with an uninformed smoothness-constrained inversion, to which a priori information was incrementally added. We found major improvements when (1) smoothness regularization constraints were relaxed (or disconnected) along boreholes and fractures, (2) a homogeneous conductivity was assumed along boreholes, and (3) borehole conductivity constraints that could be determined from a specific conductance log were applied. We also evaluated the effect of including borehole packers on fracture zone model recovery. We found that the fracture zone conductivities with the inclusion of packers were comparable to similar trials excluding the use of packers regardless of electrical potential changes. The misplacement of fracture regularization disconnects (FRDs) can easily be misinterpreted as actual fracture locations. Conductivities within these misplaced disconnects were near the starting model value, and removing smoothing between boreholes and assumed fracture locations helped in identifying incorrectly located FRDs. We found that structural constraints used after careful evaluation of a priori information are critical to improve imaging of fracture electrical conductivities, locations, and orientations.

Innovative Approach to Information Search by Example of a Patent Analysis of an Important Substitution Plan

2020 ◽  
pp. 143-157
Author(s):  
Maria A. Milkova
Keyword(s):  
Information Search ◽  
Topic Modeling ◽  
Cognitive Biases ◽  
A Priori ◽  
Import Substitution ◽  
Innovative Approach ◽  
Iterative Search ◽  
Comprehensive Picture ◽  
Priori Information ◽  
Selection Of

Nowadays the process of information accumulation is so rapid that the concept of the usual iterative search requires revision. Being in the world of oversaturated information in order to comprehensively cover and analyze the problem under study, it is necessary to make high demands on the search methods. An innovative approach to search should flexibly take into account the large amount of already accumulated knowledge and a priori requirements for results. The results, in turn, should immediately provide a roadmap of the direction being studied with the possibility of as much detail as possible. The approach to search based on topic modeling, the so-called topic search, allows you to take into account all these requirements and thereby streamline the nature of working with information, increase the efficiency of knowledge production, avoid cognitive biases in the perception of information, which is important both on micro and macro level. In order to demonstrate an example of applying topic search, the article considers the task of analyzing an import substitution program based on patent data. The program includes plans for 22 industries and contains more than 1,500 products and technologies for the proposed import substitution. The use of patent search based on topic modeling allows to search immediately by the blocks of a priori information – terms of industrial plans for import substitution and at the output get a selection of relevant documents for each of the industries. This approach allows not only to provide a comprehensive picture of the effectiveness of the program as a whole, but also to visually obtain more detailed information about which groups of products and technologies have been patented.

scholarly journals Computational Method for Wavefront Sensing Based on Transport-Of-Intensity Equation

Photonics ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 177
Author(s):  
Iliya Gritsenko ◽  
Michael Kovalev ◽  
George Krasin ◽  
Matvey Konoplyov ◽  
Nikita Stsepuro
Keyword(s):  
A Priori ◽  
Spherical Wave ◽  
Computational Method ◽  
Optical Systems ◽  
Radius Of Curvature ◽  
Imaging Method ◽  
Wavefront Sensing ◽  
Phase Imaging ◽  
Transport Of Intensity Equation ◽  
Priori Information

Recently the transport-of-intensity equation as a phase imaging method turned out as an effective microscopy method that does not require the use of high-resolution optical systems and a priori information about the object. In this paper we propose a mathematical model that adapts the transport-of-intensity equation for the purpose of wavefront sensing of the given light wave. The analysis of the influence of the longitudinal displacement z and the step between intensity distributions measurements on the error in determining the wavefront radius of curvature of a spherical wave is carried out. The proposed method is compared with the traditional Shack–Hartmann method and the method based on computer-generated Fourier holograms. Numerical simulation showed that the proposed method allows measurement of the wavefront radius of curvature with radius of 40 mm and with accuracy of ~200 μm.

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