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Airborne Electromagnetic Surveys

A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Remote Sensing in Geology, Geomorphology and Hydrology".

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 23982

Special Issue Editors


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Guest Editor
Federal Institute for Geosciences and Natural Resources
Interests: airborne geophysics; airborne electromagnetics; groundwater and soil surveys

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Guest Editor
Federal Institute for Geosciences and Natural Resources
Interests: frequency and time domain airborne electromagnetics; semi-airborne electromagnetics

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Guest Editor
Aarhus Geophysics, I-GIS Voldbjergvej, 14A, 1, sal - 8240, Risskov, Denmark
Interests: different applications of airborne electromagnetics

Special Issue Information

Dear Colleagues,

Airborne geophysical devices are being increasingly applied to quickly investigate large areas of subsurface at relatively low costs. From the most common airborne methods currently used, airborne electromagnetics (AEM) contributes most to high-resolution spatial subsurface investigations. AEM links areal remote sensing applications with local in-situ measurements. As the principal parameter investigated, the electrical conductivity, depends on various sources such as pore water salinity, clay content, or metals, AEM can be used for groundwater, soil, or mineral exploration studies.

We are interested in receiving high quality submissions that use large-scale AEM surveys to study the subsurface conductivity distribution and further applications derived from AEM results. In particular, we are looking for contributions that combine multiple parameters to investigate the near surface. Thus, joint interpretations of results of remote sensing, airborne- and ground-based surveys, as well as in-situ measurements are welcome. We are also interested in receiving submissions that use modern interpretation techniques such as cluster analyses and neuronal networks or further machine learning applications.

We look forward to receiving your manuscript.

Sincerely,

Dr. Bernhard Siemon
Dr. Annika Steuer
Dr. Andrea Viezzoli
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Airborne geophysical surveys
  • Electrical conductivity/resistivity
  • Near-surface applications
  • Large-scale soil mapping
  • Large-scale groundwater mapping
  • Large-scale geological mapping

Published Papers (7 papers)

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Research

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23 pages, 11371 KiB  
Article
1D Stochastic Inversion of Airborne Time-Domain Electromagnetic Data with Realistic Prior and Accounting for the Forward Modeling Error
by Peng Bai, Giulio Vignoli and Thomas Mejer Hansen
Remote Sens. 2021, 13(19), 3881; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13193881 - 28 Sep 2021
Cited by 12 | Viewed by 2977
Abstract
Airborne electromagnetic surveys may consist of hundreds of thousands of soundings. In most cases, this makes 3D inversions unfeasible even when the subsurface is characterized by a high level of heterogeneity. Instead, approaches based on 1D forwards are routinely used because of their [...] Read more.
Airborne electromagnetic surveys may consist of hundreds of thousands of soundings. In most cases, this makes 3D inversions unfeasible even when the subsurface is characterized by a high level of heterogeneity. Instead, approaches based on 1D forwards are routinely used because of their computational efficiency. However, it is relatively easy to fit 3D responses with 1D forward modelling and retrieve apparently well-resolved conductivity models. However, those detailed features may simply be caused by fitting the modelling error connected to the approximate forward. In addition, it is, in practice, difficult to identify this kind of artifacts as the modeling error is correlated. The present study demonstrates how to assess the modelling error introduced by the 1D approximation and how to include this additional piece of information into a probabilistic inversion. Not surprisingly, it turns out that this simple modification provides not only much better reconstructions of the targets but, maybe, more importantly, guarantees a correct estimation of the corresponding reliability. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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23 pages, 48585 KiB  
Article
3D Wavelet Finite-Element Modeling of Frequency-Domain Airborne EM Data Based on B-Spline Wavelet on the Interval Using Potentials
by Lingqi Gao, Changchun Yin, Ning Wang, Jiao Zhu, Yunhe Liu, Xiuyan Ren, Bo Zhang and Bin Xiong
Remote Sens. 2021, 13(17), 3463; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13173463 - 01 Sep 2021
Cited by 1 | Viewed by 1808
Abstract
We present a wavelet finite-element method (WFEM) based on B-spline wavelets on the interval (BSWI) for three-dimensional (3D) frequency-domain airborne EM modeling using a secondary coupled-potential formulation. The BSWI, which is constructed on the interval (0, 1) by joining piecewise B-spline polynomials between [...] Read more.
We present a wavelet finite-element method (WFEM) based on B-spline wavelets on the interval (BSWI) for three-dimensional (3D) frequency-domain airborne EM modeling using a secondary coupled-potential formulation. The BSWI, which is constructed on the interval (0, 1) by joining piecewise B-spline polynomials between nodes together, has proved to have excellent numerical properties of multiresolution and sparsity and thus is utilized as the basis function in our WFEM. Compared to conventional basis functions, the BSWI is able to provide higher interpolating accuracy and boundary stability. Furthermore, due to the sparsity of the wavelet, the coefficient matrix obtained by BSWI-based WFEM is sparser than that formed by general FEM, which can lead to shorter solution time for the linear equations system. To verify the accuracy and efficiency of our proposed method, we ran numerical experiments on a half-space model and a layered model and compared the results with one-dimensional (1D) semi-analytic solutions and those obtained from conventional FEM. We then studied a synthetic 3D model using different meshes and BSWI basis at different scales. The results show that our method depends less on the mesh, and the accuracy can be improved by both mesh refinement and scale enhancement. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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30 pages, 11682 KiB  
Article
An Assessment of Water Sources for Heritage Listed Organic Mound Springs in NW Australia Using Airborne Geophysical (Electromagnetics and Magnetics) and Satellite Remote Sensing Methods
by Jasmine Rutherford, Tania Ibrahimi, Tim Munday, Adrienne Markey, Andrea Viezzoli, Arianna Rapiti and Rod Paterson
Remote Sens. 2021, 13(7), 1288; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13071288 - 28 Mar 2021
Cited by 2 | Viewed by 2654
Abstract
Discrete phreatophytic vegetation associated with organic mound springs is present in several places in the semi-arid Walyarta Conservation Park (Park) in northern Western Australia. The mound springs are heritage listed, having significant cultural and environmental significance. Increased industrial (mining and agriculture) development in [...] Read more.
Discrete phreatophytic vegetation associated with organic mound springs is present in several places in the semi-arid Walyarta Conservation Park (Park) in northern Western Australia. The mound springs are heritage listed, having significant cultural and environmental significance. Increased industrial (mining and agriculture) development in the region, coupled with a growing demand for groundwater to support these developments, requires an enhanced understanding of how the springs operate and the source of water that sustains their presence. The springs are broadly believed to be situated on geological faults and receive groundwater from artesian sources. However, their association with deeper geological structures and aquifer systems, the focus of this study, is not well understood. This study employed regional- and finer-scale airborne geophysical data, including electromagnetics (AEM) and magnetics, to constrain the sub-basin-scale hydrogeology of the West Canning Basin in Western Australia and to detail tectonic deformation, sedimentological and hydrological processes. The AEM data were inverted using 1- and 2D methods to better define structural discontinuities in the Park, and the results identified the location of faults and other geological structures that were coincident with spring locations. A complementary analysis of spatiotemporal patterns of green vegetation was undertaken using remote sensing data. A model for the extent of green vegetation (in percent), calculated using a constrained linear spectral unmixing algorithm and applied to a select Landsat Thematic Mapper ™ image archive, showed the persistence of green vegetation aligned with interpreted fault systems through extended dry periods. These geophysical and remotely sensed datasets demonstrate that in the Park, the sedimentary aquifers and landscapes are highly compartmentalized and that this constrains aquifer distribution, groundwater quality and the location of wetlands and phreatophytic vegetation. Integrating key information from these datasets allows for the construction of a three-dimensional model that predicts the nature and extent of the critical zone which sustains perennial groundwater discharge within mound springs, drainages and wetlands and provides a framework to assess discharge rates, mixing and, ultimately, sensitivity to changed water availability. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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15 pages, 9531 KiB  
Article
Application of Airborne Electromagnetics and Magnetics for Mineral Exploration in the Baishiquan–Hongliujing Area, Northwest China
by Shengjun Liang, Siyuan Sun and Hongfei Lu
Remote Sens. 2021, 13(5), 903; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13050903 - 27 Feb 2021
Cited by 8 | Viewed by 3100
Abstract
Airborne electromagnetics is an effective and efficient exploration tool in shallow mineral exploration for its high efficiency and low cost. In 2016, airborne electromagnetic and airborne magnetic surveys have been carried out at the border of Xinjiang Uygur Autonomous Region and Gansu Province, [...] Read more.
Airborne electromagnetics is an effective and efficient exploration tool in shallow mineral exploration for its high efficiency and low cost. In 2016, airborne electromagnetic and airborne magnetic surveys have been carried out at the border of Xinjiang Uygur Autonomous Region and Gansu Province, the Northwest China. With an integrated system, the airborne electromagnetics and airborne magnetic data were collected simultaneously by AreoTEM-IV system from Aeroquest International Limited in Vancouver, BC, Canada, and the CS3 Cesium Vapor magnetometer from Scintrex in Concord, ON, Canada. About 3149 line-km of both data with 250 m line space were acquired. After data processing, the comprehensive analysis and interpretation of resistivity and magnetic anomalies has been carried out to infer lithological structure and outline the potential ore deposits. Verified by the ground surveys, seven outlined anomalies are consistent with the known ore sites, and one new gold deposit and several mineralization clues were found. The prospective reserves of gold are expected to exceed 10 tons. Besides, some prospecting target areas were outlined as the possible locations of copper–nickel deposits. The successful case shows the airborne magnetic data accords with geological structures, and the airborne electromagnetic method is effective in finding metal mineral resources, which can help to quickly identify potential ore targets with no surface outcrop. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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18 pages, 24014 KiB  
Article
3D Airborne EM Forward Modeling Based on Time-Domain Spectral Element Method
by Changchun Yin, Zonghui Gao, Yang Su, Yunhe Liu, Xin Huang, Xiuyan Ren and Bin Xiong
Remote Sens. 2021, 13(4), 601; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13040601 - 08 Feb 2021
Cited by 2 | Viewed by 1956
Abstract
Airborne electromagnetic (AEM) method uses aircraft as a carrier to tow EM instruments for geophysical survey. Because of its huge amount of data, the traditional AEM data inversions take one-dimensional (1D) models. However, the underground earth is very complicated, the inversions based on [...] Read more.
Airborne electromagnetic (AEM) method uses aircraft as a carrier to tow EM instruments for geophysical survey. Because of its huge amount of data, the traditional AEM data inversions take one-dimensional (1D) models. However, the underground earth is very complicated, the inversions based on 1D models can frequently deliver wrong results, so that the modeling and inversion for three-dimensional (3D) models are more practical. In order to obtain precise underground electrical structures, it is important to have a highly effective and efficient 3D forward modeling algorithm as it is the basis for EM inversions. In this paper, we use time-domain spectral element (SETD) method based on Gauss-Lobatto-Chebyshev (GLC) polynomials to develop a 3D forward algorithm for modeling the time-domain AEM responses. The spectral element method combines the flexibility of finite-element method in model discretization and the high accuracy of spectral method. Starting from the Maxwell's equations in time-domain, we derive the vector Helmholtz equation for the secondary electric field. We use the high-order GLC vector interpolation functions to perform spectral expansion of the EM field and use the Galerkin weighted residual method and the backward Euler scheme to do the space- and time-discretization to the controlling equations. After integrating the equations for all elements into a large linear equations system, we solve it by the multifrontal massively parallel solver (MUMPS) direct solver and calculate the magnetic field responses by the Faraday's law. By comparing with 1D semi-analytical solutions for a layered earth model, we validate our SETD method and analyze the influence of the mesh size and the order of interpolation functions on the accuracy of our 3D forward modeling. The numerical experiments for typical models show that applying SETD method to 3D time-domain AEM forward modeling we can achieve high accuracy by either refining the mesh or increasing the order of interpolation functions. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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25 pages, 14661 KiB  
Article
Airborne Electromagnetic, Magnetic, and Radiometric Surveys at the German North Sea Coast Applied to Groundwater and Soil Investigations
by Bernhard Siemon, Malte Ibs-von Seht, Annika Steuer, Nico Deus and Helga Wiederhold
Remote Sens. 2020, 12(10), 1629; https://0-doi-org.brum.beds.ac.uk/10.3390/rs12101629 - 19 May 2020
Cited by 16 | Viewed by 6535
Abstract
The knowledge of the subsurface down to about one hundred meters is fundamental for a variety of economic, ecological, and geoscientific tasks, particularly in coastal zones. Marine and terrestrial processes influence coastal zones and both seawater intrusion and submarine freshwater discharges may occur. [...] Read more.
The knowledge of the subsurface down to about one hundred meters is fundamental for a variety of economic, ecological, and geoscientific tasks, particularly in coastal zones. Marine and terrestrial processes influence coastal zones and both seawater intrusion and submarine freshwater discharges may occur. The Federal Institute for Geosciences and Natural Resources (BGR) conducted airborne geophysical surveys in the coastal region of the German Bight between 2000 and 2014. The helicopter-borne system used simultaneously collected electromagnetic (HEM), magnetic (HMG), and radiometric (HRD) data. An area of about 5900 km2 was covered with parallel flight lines at 250 m line separation and additional tie-lines at larger separations. In total, about 25,000 km of data at sampling distances of 4 m (HEM, HMG) and 40 m (HRD) were acquired. The electrical resistivity (HEM), the anomalies of the magnetic field (HMG), and the exposure rate (HRD) are the resulting geophysical parameters derived from the data. The results are displayed as maps of the geophysical parameters as well as vertical resistivity sections (only HEM). Both data and products are publicly available via BGR’s product center. The airborne geophysical results helped to outline the fresh–saline groundwater interface, freshwater lenses on islands, submarine groundwater discharges, buried tunnel valleys, mires, and ancient landscapes. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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Review

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25 pages, 6490 KiB  
Review
AEM in Norway: A Review of the Coverage, Applications and the State of Technology
by Edward J. Harrison, Vikas C. Baranwal, Andreas A. Pfaffhuber, Craig W. Christensen, Guro H. Skurdal, Jan Steinar Rønning, Helgard Anschütz and Marco Brönner
Remote Sens. 2021, 13(22), 4687; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13224687 - 19 Nov 2021
Cited by 2 | Viewed by 2937
Abstract
From the first use of airborne electromagnetic (AEM) systems for remote sensing in the 1950s, AEM data acquisition, processing and inversion technology have rapidly developed. Once used extensively for mineral exploration in its early days, the technology is increasingly being applied in other [...] Read more.
From the first use of airborne electromagnetic (AEM) systems for remote sensing in the 1950s, AEM data acquisition, processing and inversion technology have rapidly developed. Once used extensively for mineral exploration in its early days, the technology is increasingly being applied in other industries alongside ground-based investigation techniques. This paper reviews the application of onshore AEM in Norway over the past decades. Norway’s rugged terrain and complex post-glacial sedimentary geology have contributed to the later adoption of AEM for widespread mapping compared to neighbouring Nordic countries. We illustrate AEM’s utility by using two detailed case studies, including time-domain and frequency domain AEM. In both cases, we combine AEM with other geophysical, geological and geotechnical drillings to enhance interpretation, including machine learning methods. The end results included bedrock surfaces predicted with an accuracy of 25% of depth, identification of hazardous quick clay deposits, and sedimentary basin mapping. These case studies illustrate that although today’s AEM systems do not have the resolution required for late-phase, detailed engineering design, AEM is a valuable tool for early-phase site investigations. Intrusive, ground-based methods are slower and more expensive, but when they are used to complement the weaknesses of AEM data, site investigations can become more efficient. With new developments of drone-borne (UAV) systems and increasing investment in AEM surveys, we see the potential for continued global adoption of this technology. Full article
(This article belongs to the Special Issue Airborne Electromagnetic Surveys)
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