A cut-&amp;-paste strategy for the 3-D inversion of helicopter-borne electromagnetic data — I. 3-D inversion using the explicit Jacobian and a tensor-based formulation

Scheunert, M.; Ullmann, A.; Afanasjew, M.; Börner, Ralph-Uwe; Siemon, B.; Spitzer, Klaus

doi:10.1016/j.jappgeo.2016.03.023

Cited by 11 publications

(4 citation statements)

References 46 publications

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“…As hydrogeophysical investigations are often conducted in areas with young, horizontal or subhorizontal substrata, physical property contrasts are generally horizontally smoothly varying. Furthermore, depending on system altitude, system frequency, and subsurface EC (Tølbøll & Christensen, 2007), HEM systems have a relatively small footprint (~100-200 m); therefore, the benefits of 2-D (e.g., Boesen et al, 2018;Li et al, 2016) and 3-D (e.g., Cox et al, 2012;Scheunert et al, 2016) inversions are limited and considered to be impractical compared to the less computationally expensive 1-D techniques. As a result, this study will focus on 1-D inversion methods only.…”

Section: Geophysical Inversionsmentioning

confidence: 99%

“…To obtain useful quantitative data, AEM measurements need to be converted into an EC distribution, and ultimately a groundwater salinity estimate, or to map hydrostratigraphy—this is undertaken using a process called inversion. In AEM mapping programs, a number of inversion algorithms are available for this purpose, which include 1‐D methods (Farquharson et al, ; Siemon, Auken, et al, ; Vignoli et al, ) or more complex 2‐D (Hermans et al, ) and 3‐D (Cox et al, ; Scheunert et al, ) inversions. To validate new inversion techniques (or improvements on existing algorithms), these are typically tested using a synthetic model and then applied to an area where relatively little is known about the subsurface (Auken et al, ; Farquharson et al, ; Siemon, Auken, et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Quantifying Geophysical Inversion Uncertainty Using Airborne Frequency Domain Electromagnetic Data—Applied at the Province of Zeeland, the Netherlands

King

Essink

Karaolis

et al. 2018

Water Resources Research

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An accurate understanding of the fresh‐saline distribution of groundwater is necessary for effective groundwater management. Airborne electromagnetic (AEM) surveys offer a rapid and cost‐effective method with which to map this, offering valuable additional information about the subsurface. To convert AEM data into electric conductivity and ultimately groundwater salinity, an inversion is undertaken. A number of algorithms are available for this purpose; however, these are affected by significant uncertainty, owing to inherent nonunique characteristics of this process. The most commonly used inversion codes in hydrogeophysical studies were quantitatively tested using frequency domain AEM and ground data from the province of Zeeland, the Netherlands. These include UBC1DFM code and quasi‐2D laterally constrained inversions. Following an investigation of inversion parameter settings, data were inverted for four inversion methods and interpolated into 3‐D volumes. Using geological data and empirical electrical conductivity and water salinity relationships, each inversion was converted into groundwater electrical conductivity and split into fresh‐brackish‐saline regions. For groundwater volume estimates out of a total volume of 2.8 billion m3, a fresh groundwater estimate could differ by as much as 178 million m3, depending on the inversion used. The primary factor here was the choice of model smoothness, which was shown to affect the thickness of the brackish interval. Fresh‐brackish‐saline interfaces were consistently mapped with an accuracy of ~3 m, the brackish being the most accurately resolved. The few layer method was less successful at resolving smoothly varying salinity distributions but more successful at mapping the brackish interface at greater depth.

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Section: Geophysical Inversionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantifying Geophysical Inversion Uncertainty Using Airborne Frequency Domain Electromagnetic Data—Applied at the Province of Zeeland, the Netherlands

King

Essink

Karaolis

et al. 2018

Water Resources Research

View full text Add to dashboard Cite

show abstract

“…As hydrogeophysical investigations are oft en conducted in areas with young, horizontal or subhorizontal substrata, physical property contrasts are generally horizontally smoothly varying. Furthermore, depending on system altitude, system frequency, and subsurface EC (Tølbøll and Christensen, 2007), HEM systems have a relatively small footprint (~100-200 m); therefore, the benefi ts of 2-D (e.g., Boesen et al, 2018;Li et al, 2016) and 3-D (e.g., Cox et al, 2012;Scheunert et al, 2016) inversions are limited and considered to be impractical compared to the less computationally expensive 1-D techniques. As a result, this study will focus on 1-D inversion methods only.…”

Section: Geophysical Inversionsmentioning

confidence: 99%

“…To obtain useful quantitative data, AEM measurements need to be converted into an EC distribution, and ultimately a groundwater salinity estimate, or to map hydrostratigraphy-this is undertaken using a process called inversion. In AEM mapping programs, a number of inversion algorithms are available for this purpose, which include 1-D methods (Farquharson et al, 2003;Siemon et al, 2009a;Vignoli et al, 2015), or more complex 2-D (Hermans et al, 2012) and 3-D (Cox et al, 2012;Scheunert et al, 2016) inversions. To validate new inversion techniques (or improvements on existing algorithms), these are typically tested using a synthetic model and then applied to an area where relatively little is known about the subsurface (Auken et al, 2005;Farquharson et al, 2003;Siemon et al, 2009a).…”

Section: Introductionmentioning

confidence: 99%

Airborne electromagnetic mapping of coastal groundwater salinity

King¹

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Low elevation coastal zones (LECZs), defined here as areas ≤10 m above mean sea-level, have attracted people for millennia. With their abundant resources and access to trading ports, today these areas host nearly 800 million people – a figure that is predicted to rise to 1.4 billion by 2060. Naturally, it follows that with population growth comes an increased demand for freshwater. Globally, about 50% of the world’s population rely on groundwater to satisfy basic requirements – and LECZs are no exception. However, owing to anthropogenic activity, these aquifers are highly stressed and vulnerable to saltwater intrusion – where freshwater can be displaced by saline groundwater. As a result, aquifers within LECZs require effective management, which in turn requires an excellent regional understanding of fresh-saline groundwater distributions. Airborne electromagnetic (AEM) surveys offer a rapid and cost- effective method to map this, and thus are increasingly used for these purposes. Despite increasing popularity, AEM is relatively poorly understand in terms of regional (provincial or country scale) groundwater salinity mapping. The primary objective of this thesis is therefore twofold: 1) to better understand the uncertainties involved and 2), use this understanding to develop novel mapping methods. Consequently, the following research questions were formulated: 1. What is the effect of using different inversion methods and parameters on mapping results? 2. How are results affected by different quantities of available data? 3. Based on the results of chapters 2 and 3, what further methodological improvements can we make? 4. Are groundwater salinity movements sensitive to repeated AEM surveys? To answer these research questions, I used data from the Province of Zeeland, The Netherlands. Zeeland experienced sea-level transgressions in the early Holocene, followed by the construction of by man-made coastal defences – which allowed the recent freshening of shallow aquifers. As a result, much of Zeeland comprises shallow rainwater lenses (often as little as 1 – 2m thick), and therefore offers a fascinating study area for applied groundwater research. Furthermore, a recently undertaken, high quality AEM survey and plentiful ground-based data provide an ideal testing ground. Throughout the thesis, these data were used either directly, or as basis for the construction of highly detailed synthetic models.

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Anisotropic complex electrical conductivity of black shale and mudstone from the Moffat Shale Group (Ireland)

Römhild

Sonntag

Kiyan

et al. 2019

Near Surface Geophysics

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The geological setting in the north of Ireland, especially concerning the origin of the Moffat Shale Group, has long been under discussion. Within the Tellus Programme of the Geological Survey Ireland, airborne electromagnetic measurements revealed high‐conductivity anomalies that have been interpreted as the response of a black shale. In order to petrophysically characterize the Moffat Shale, a laboratory study using material from two shallow boreholes was carried out. The study focuses on spectral induced polarization measurements on 23 oriented samples in the frequency range from 10−4 to 105 Hz. The sample material can be categorized into two groups. A mudstone‐like rock type shows weakly frequency‐dependent, porosity‐driven conductivities with a strong anisotropy. On the other hand, black shale samples are characterized by moderately anisotropic but strong polarization effects especially at low frequencies and a strong conductivity increase towards higher frequencies. The polarization in the black shale is controlled by the texture and volume fraction of the polarizable components. The spectral induced polarization data are processed by means of a Debye decomposition approach. The anisotropy of the complex electrical conductivity is determined by utilizing the foliation dip angle and assuming tilted transverse isotropic conditions. The relevance of the laboratory findings for airborne electromagnetic surveys is addressed with a synthetic one‐dimensional modelling study.

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A cut-&-paste strategy for the 3-D inversion of helicopter-borne electromagnetic data — I. 3-D inversion using the explicit Jacobian and a tensor-based formulation

Cited by 11 publications

References 46 publications

Quantifying Geophysical Inversion Uncertainty Using Airborne Frequency Domain Electromagnetic Data—Applied at the Province of Zeeland, the Netherlands

Quantifying Geophysical Inversion Uncertainty Using Airborne Frequency Domain Electromagnetic Data—Applied at the Province of Zeeland, the Netherlands

Airborne electromagnetic mapping of coastal groundwater salinity

Anisotropic complex electrical conductivity of black shale and mudstone from the Moffat Shale Group (Ireland)

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