Comparison of Ert, Ground-Based Towed Tem and Airborne Tem Resistivity Mapping
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Summary Electrical resistivity tomography (ERT) and time domain electromagnetic (TEM) are two widely adopted geophysical methods for near surface resistivity mapping. However, the results produced by the two may differ due to fundamental differences in physical principles, sensitivity, system geometry. The main objective of this paper is to provide a one-to-one comparison of ERT against a newly developed towed TEM system tTEM and comparison of tTEM against its airborne counterpart SkyTEM. We compare three methods using both synthetic as well as field data. Overall, we found that inversion results are comparable across the three methods. They all capture the prominent features of synthetic models. The ERT and tTEM inversion of field data show very comparable results even in the top 5 m where both can image thin resistive layers. However, the resistivity of the thin resistive layer is better resolved using ERT because of its high sensitivity close to the surface. In deeper part of the profile, tTEM tends to produce better resolved boundaries compared to the ERT method. Comparing the SkyTEM inversion results against the tTEM, shows that tTEM has a better vertical and horizontal resolution in the top 20 m.Keywords:
Resistive touchscreen
Electrical Resistivity Tomography
SUMMARY Electrical and electromagnetic methods are well suited for mapping the top 100 m of the subsurface, particularly electrical resistivity tomography (ERT) and Traseint electromagnetic (TEM). Both methods can provide comparable resolution and depth of investigation for generating continuous 2-D resistivity profiles. TEM measurements taken continuously from moving platforms, whether towed on the ground or airborne, can generate 2-D-like resistivity sections similar to those produced by ERT profiling. However, despite the fact that both ERT and TEM can map the electrical resistivity of the subsurface, their results differ due to fundamental differences in physical principles, sensitivity, system geometry and instrumentation. The main objective of this paper is to provide a one-on-one comparison of the newly developed towed TEM system, tTEM, against ERT and airborne TEM, in our case a SkyTEM system. First, we performed the comparison in terms of model resolution using synthetic data and models. For all methods, synthetic data were generated using a 1-D forward response, and inversions were carried out using smooth layered models in a laterally constrained inversion framework. Overall, the inversion results are comparable across the three methods, and they all capture the key features of the synthetic models. The ERT and tTEM cross-sections from two field cases show very comparable results even in the top 5 m where thin resistive layers (∼60 Ω·m) are clearly mapped by both methods. However, the resistivity of the resistive layer is better resolved using ERT than tTEM because of the high sensitivity close to the surface in the ERT case. In the deeper part of the section, tTEM tends to resolve the boundaries of conductive layers (resistivity < 10 Ω·m) better than the ERT method. Compared to SkyTEM, tTEM has a better vertical and horizontal resolution especially in the top 20 m. The better tTEM resolution compared to SkyTEM is primarily due to a smaller footprint and denser data sampling. Depth of investigation-wise the SkyTEM system is superior compared to tTEM due to its larger magnetic moment.
Electrical Resistivity Tomography
Resistive touchscreen
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Abstract Inhomogeneity caused by fractures can constitute real problems in foundation soils which consequently can lead to structural failure. 2D Electrical Resistivity Tomography (ERT) has been exceedingly popular in mapping near surface discontinuities that can possibly affect engineering structures. The effectiveness of using Induced Polarisation Tomography (IPT) in mapping subsurface fractures was explored. Using the same field way out for both ERT and IPT, investigations were carried out at a failed structure with foundational inhomogeneity in the Nsukka area, Southeastern Nigeria. Four Electrical Resistivity Tomography (ERT) and four Induced Polarisation Tomography (IPT) were carried out. Electrical Resistivity Tomography for profile line one (ERT 1 ) and that of the opposite section, ERT 3 , revealed a fault trending NNW- SSE. This anomaly was also observed on the Induced Polarization Tomography for profile line one (IPT 1 ) as well as that of profile line three (IPT 3 ) at the same offset distances, delineating the same fracture zone. A second fault trending in NE-SW was mapped by the Electrical Resistivity Tomography for profile line two (ERT 2 ) and Electrical Resistivity Tomography for profile line four (ERT 4 ). The fault was also visible in the Induced Polarization counterparts, IPT 2 and IPT 4 . Field validation along mapped trends recorded subtle cracks on the foundation along the same trend detected by the IPT as well as the ERT.
Electrical Resistivity Tomography
Classification of discontinuities
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Electrical Resistivity Tomography
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Electrical Resistivity Tomography
Electrical Impedance Tomography
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A devastating rainfall, commencing on 13 May 2014, resulted in extensive flooding of Serbia, Bosnia and Herzegovina (BiH). Several days after the torrential rainfall a hundreds of landslides developed. To investigate the landslides a suite of geophysical methods including reflection, refraction, Multi-channel analysis of surface waves (MASW) and Electrical Resistivity Tomography (ERT) were deployed. Seismic reflection surveys are deployed to map layers geometry and discontinuities. MASW to help with geotechnical properties. ERT to bring lithological information into the analysis. Electrical Resistivity Tomography (ERT) is routinely used for the near-surface exploration of landslide areas. However, it rarely used in a time-lapse manner which is of interest for investigation of potential landslide reactivations and the mechanism of reactivation. This paper presents the results obtained from time-lapse 2D ERT (TL-ERT) for the investigation of landslides. Repeated 2D surveys are carried out to detect temporal (seasonal) changes of the content of fluids and to more fully understand influence on resistivity of the subsurface. Presentation Date: Tuesday, September 26, 2017 Start Time: 9:45 AM Location: 370C Presentation Type: ORAL
Electrical Resistivity Tomography
Reflection
Classification of discontinuities
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Electrical resistivity tomography (ERT) has been widely applied in hydrology during recent years with its high efficiency and precision. Based on summary and analysis the huge number of bibliographies,considering the complicated factors that affect the electrical resistivity underground,the relationship between the resisitivity and hydraulic parameters,such as water content,hydraulic conductivity,porosity,solution and so on,have been listed in this thesis,emphasizing on the application of ERT on water resource surveying,the solute transportation monitoring,hydraulic parameters inversion. Aiming at the problems that are still existing,we have tried our best to supply some suggestions for discussing together.
Electrical Resistivity Tomography
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