Articles | Volume 13, issue 1
https://doi.org/10.5194/gi-13-27-2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gi-13-27-2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
An optimized and hybrid gating scheme for the suppression of very low-frequency radios in transient electromagnetic systems
Smith Kashiram Khare
Department of Electrical and Computer Engineering, Aarhus University, Finlandsgade 22, 8200 Aarhus N, Denmark
Paul McLachlan
Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, 8000 Aarhus C, Denmark
Pradip Kumar Maurya
TEMcompany, Aarhus, Vester Søgaardsvej 22, 8230 Aarhus, Denmark
Department of Electrical and Computer Engineering, Aarhus University, Finlandsgade 22, 8200 Aarhus N, Denmark
WATEC, Aarhus University Centre for Water Technology, Ny Munkegade 120, 8000 Aarhus C, Denmark
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This work presents simulations, modelling, and experimental verification of a novel steady-state surface nuclear magnetic resonance (NMR) transmitter used for the non-invasive exploration of groundwater. The paper focuses on three main aspects of high-current transmitter instrumentation: thermal management, current-drooping, and pulse stability. This work will interest readers involved in geoscientific instrument prototyping for groundwater exploration using portable geoscientific instruments.
Mathias Vang, Jakob Juul Larsen, Anders Vest Christiansen, and Denys Grombacher
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To manage groundwater effectively, it's important to understand subsurface water systems. Geophysical methods can characterize subsurface layers, but relying on just one method can be misleading. This study combines two methods – Transient electromagnetics and surface nuclear magnetic resonance – in a K-means clustering scheme to better resolve freshwater and saltwater zones. Two case studies showed how a combined approach improves characterization of these hydrogeological important layers.
Mathias Vang, Denys Grombacher, Matthew P. Griffiths, Lichao Liu, and Jakob Juul Larsen
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In this paper, we use a novel surface nuclear magnetic resonance (SNMR) method for rapid high-quality data acquisition. The SNMR results from more than 100 soundings in three different case studies were used to map groundwater. The soundings successfully track the water table through the three areas and are compared to boreholes and other geophysical measurements. The study highlights the use of SNMR in hydrological surveys and as a tool for regional mapping of the water table.
Muhammad Rizwan Asif, Nikolaj Foged, Thue Bording, Jakob Juul Larsen, and Anders Vest Christiansen
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To apply a deep learning (DL) algorithm to electromagnetic (EM) methods, subsurface resistivity models and/or the corresponding EM responses are often required. To date, there are no standardized EM datasets, which hinders the progress and evolution of DL methods due to data inconsistency. Therefore, we present a large-scale physics-driven model database of geologically plausible and EM-resolvable subsurface models to incorporate consistency and reliability into DL applications for EM methods.
M. Andy Kass, Esben Auken, Jakob Juul Larsen, and Anders Vest Christiansen
Geosci. Instrum. Method. Data Syst., 10, 313–323, https://doi.org/10.5194/gi-10-313-2021, https://doi.org/10.5194/gi-10-313-2021, 2021
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We have developed a towed magnetic gradiometer system for rapid acquisition of magnetic and magnetic gradient maps. This high-resolution system is flexible and has applications to utility detection, archaeology, unexploded ordnance, or any other applications where high-resolution maps of the magnetic field or gradient are required. Processing of the data has been simplified as much as possible to facilitate rapid results and interpretations.
Jakob Juul Larsen, Stine Søgaard Pedersen, Nikolaj Foged, and Esben Auken
Geosci. Instrum. Method. Data Syst., 10, 81–90, https://doi.org/10.5194/gi-10-81-2021, https://doi.org/10.5194/gi-10-81-2021, 2021
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The transient electromagnetic method (TEM) is widely used for mapping subsurface resistivity structures, but data are inevitably contaminated by noise from various sources including radio signals in the very low frequency (VLF) 3–30 kHz band. We present an approach where VLF noise is effectively suppressed with a new post-processing scheme where boxcar gates are combined into semi-tapered gates. The result is a 20 % increase in the depth of investigation for the presented test survey.
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Short summary
Data recorded with transient electromagnetics are typically gated to improve the signal-to-noise ratio. Gating corresponds to low-pass filtering of data with the shape of the gate giving the frequency response. We show that standard gate shapes can lead to significant correlation between gates caused by distortion from VLF radios. A multi-objective cost function is used to select optimum gate shapes with less influence from radio noise. Performance is demonstrated using synthetic and field data.
Data recorded with transient electromagnetics are typically gated to improve the signal-to-noise...