Interpretation of shallow electromagnetic instruments resistivity and magnetic susceptibility measurements using rapid 1D/3D inversion

Benech, Christophe; Dabas, Michel; Simon, François Xavier; Tabbagh, Alain; Thiesson, Julien

doi:10.1190/geo2014-0549.1

Cited by 14 publications

(3 citation statements)

References 28 publications

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“…Given that any electromagnetic (EM) method in the low frequency range [16] is diffusive and integrates a large volume based on the footprint of the system, this approach will inevitably smoothen out real soil structures. A few authors have suggested to perform a full inversion of the EMI data without assuming the LIN approximation [29][30][31], but it is our impression that this is not common practice. For airborne instruments of a similar type, the industry standard has been to perform a full processing and inversion of the data [32,33].…”

Section: Introductionmentioning

confidence: 99%

Improved Geoarchaeological Mapping with Electromagnetic Induction Instruments from Dedicated Processing and Inversion

et al. 2016

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Increasingly, electromagnetic induction methods (EMI) are being used within the area of archaeological prospecting for mapping soil structures or for studying paleo-landscapes. Recent hardware developments have made fast data acquisition, combined with precise positioning, possible, thus providing interesting possibilities for archaeological prospecting. However, it is commonly assumed that the instrument operates in what is referred to as Low Induction Number, or LIN. Here, we detail the problems of the approximations while discussing a best practice for EMI measurements, data processing, and inversion for understanding a paleo-landscape at an Iron Age human bone depositional site (Alken Enge) in Denmark. On synthetic as well as field data we show that soil mapping based on EMI instruments can be improved by applying data processing methodologies from adjacent scientific fields. Data from a 10 hectare study site was collected with a line spacing of 1-4 m, resulting in roughly 13,000 processed soundings, which were inverted with a full non-linear algorithm. The models had higher dynamic range in the retrieved resistivity values, as well as sharper contrasts between structural elements than we could obtain by looking at data alone. We show that the pre-excavation EMI mapping facilitated an archaeological prospecting where traditional trenching could be replaced by a few test pits at selected sites, hereby increasing the chance of finding human bones. In a general context we show that (1) dedicated processing of EMI data is necessary to remove coupling from anthropogenic structures (fences, phone cables, paved roads, etc.), and (2) that carrying out a dedicated full non-linear inversion with spatial coherency constraints improves the accuracy of resistivities and structures over using the data as they are or using the Low Induction Number (LIN) approximation.

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Section: Introductionmentioning

confidence: 99%

Improved Geoarchaeological Mapping with Electromagnetic Induction Instruments from Dedicated Processing and Inversion

et al. 2016

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“…Nevertheless, in this study, we have tried to get as much information as possible by a constrained inversion of FDEM data (Benech et al, 2016). The characteristics of sedimentary filling and depth of the limestone substrate have been interpreted from the solution The thickness of the first layer kept fix to 1.5 m, and the thickness of the second layer was considered the free variable.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Frequency Domain Electromagnetic mapping for delineating subsurface structures related to the historical port of Emporiae

Casas

Castanyer

Himi

et al. 2021

Archaeological Prospection

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In recent years, there has been a growing interest in the application of geophysical methods to reconstruct the palaeo-landscapes of sites of special historical interest in support of the planning of archaeological researches. Given the extent of the surface to be investigated, electromagnetic methods have proven to be very suitable for their speed, resolution and versatility for this objective. In particular, coastal areas of the Mediterranean have undergone significant changes in the position of the coastline, because of changes in sea level and sediment inputs that have covered natural harbours used for the establishing colonies.In this paper, we present the results of a geophysical survey conducted using frequency-domain electromagnetic (FDEM) method carried out to get the geometry of a coastal area near to Emporiae (NE, Spain), which was supposed to form a natural port that was used by Greeks and Romans for its first colonial settlements on the Iberian Peninsula. The results obtained from a dense network of apparent conductivity measurements, supported punctually by other geophysical data (VES and ERT) and boreholes, has allowed us to define the geometry of the basin and confirm the hypotheses of the existence of harbour buried under the coastal and alluvial sediments in the bay close to the remains from Greek and Roman times.

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“…The true penetration depths are a function of the topsoil conductivity which should vary with different sites(Heil and Schmidhalter, 2017;Paton, 2012). The penetration depth for MSa is much different from that of the ECa and shows a complex pattern with negative or less than background values for the horizontal coplanar response when the target's depth is less than 0.36 times transmitter-receiver separation(Benech et al, 2016;Sadatcharam et al, 2020) Sadatcharam et al (2020). showed that 90% of the cumulative response signals from vertical coplanar transmitter-receive coils with spacings of 32, 71 and 118 cm are from a theoretical depth of 30, 65 and 110 cm, validating their use for shallow investigation at less than 1 m depth.…”

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confidence: 91%

Estimating Soil Properties Distribution at a Restored Wetland Using Electromagnetic Imaging and Limited Soil Core Samples

et al. 2023

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Electromagnetic imaging (EMI) provides an e cient approach for characterizing variations in soil physicochemical properties at a high spatial resolution. While EMI has been widely used to estimate variations in soil properties in agricultural, geotechnical, and contaminated sites, limited applications have been reported for wetlands. This study assesses the use of EMI for estimating soil property distributions at a restored wetland in northwestern Ohio, USA. We acquired spatial distribution of soil apparent electrical conductivity (ECa) and apparent magnetic susceptibility (MSa) via EMI over a 162,000 m 2 restored wetland using an EM-38-MK2 instrument towed behind a utility terrain vehicle equipped with a differential ground positioning system. We collected twenty-two undisturbed soil samples and analyzed them in the laboratory for soil moisture (SMC), organic matter (SOM), porosity, bulk density, and texture. A least squares linear regression model was used to compare the correlation between each soil property with measured ECa and MSa while ECa was used to predict the distribution of SMC and SOM using the statistical model validated using the leave-one-out technique. We observed strong correlations between soil texture, SMC, and SOM, and ECa with SOM showing a slightly dominant control. This study shows that ECa can predict the distribution of SMC and SOM in wetland soils to an accuracy of ~ 67-70% for these datasets. The spatial ECa patterns matched the USDA soil map for the site. This study validates the potential of extending EMI for characterizing wetland soil properties, improving sampling plans, and extrapolating soil property estimates to unsampled regions.

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Interpretation of shallow electromagnetic instruments resistivity and magnetic susceptibility measurements using rapid 1D/3D inversion

Abstract: Interpretation of shallow EMI resistivity and magnetic susceptibility measurements using rapid 1D/3D inversion Short title: Rapid1D/3D inversion of shallow EMI

Cited by 14 publications

References 28 publications

Improved Geoarchaeological Mapping with Electromagnetic Induction Instruments from Dedicated Processing and Inversion

Improved Geoarchaeological Mapping with Electromagnetic Induction Instruments from Dedicated Processing and Inversion

Frequency Domain Electromagnetic mapping for delineating subsurface structures related to the historical port of Emporiae

Estimating Soil Properties Distribution at a Restored Wetland Using Electromagnetic Imaging and Limited Soil Core Samples

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