3. Profiling Methods Using Small Sources

Frischknecht, F.C.; Labson, Victor F.; Spies, Brian R.; Anderson, Walter L.

doi:10.1190/1.9781560802686.ch3

Cited by 122 publications

(62 citation statements)

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“…The physical model results in Figure 1(a) are normalized with respect to the signal recorded when the sensing coils are located in air at sufficient distance from any conductive structure that the response is pure real. The results for the target in free-space shown in Figure 1(a), are in good agreement with earlier published studies (NAIR et al 1968;STRANGWAY, 1966;HANNESON and WEST, 1984;FRISCHKNECHT et al, 1991). The physical model system has also been found to generate results that are in good quantitative agreement with theoretical modeling of the response of a cubic structure (FARQUHARSON et al, 2003).…”

Section: Horizontal Coplanar Coil Responsessupporting

confidence: 80%

Comparison of Theoretical and Physical Model Studies of the Responses of Moving Source and Fixed Loop Electromagnetic Exploration Systems

Duckworth

2005

Pure appl. geophys.

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Abstract-Theoretical and physical scale model responses for moving source and fixed loop electromagnetic exploration systems are presented for the case of a vertical, thin, plate conductor located first in free-space and then in a conductive host. The results are presented in the form of anomaly index diagrams plotted in complex space. The two modeling approaches show general agreement on the behavior of the current gathering effect that operates when the conductive host is present. Both approaches show an onset of a strong positive effect at higher frequencies in the responses provided by both horizontal coplanar coil systems and by fixed loop systems. Agreement is also shown on an unanticipated negative effect that a conductive host causes in the responses provided by the vertical coplanar coincident coil system. Both modeling approaches demonstrate that the responses provided by fixed loop systems are predominantly caused by the current gathering effect. The extent of this effect for fixed loop systems depends on the size of the transmitter loop with respect to the target and on the depth of the target. The theoretical modeling demonstrates that both moving source and fixed loop systems operated over a target located in a conductive host, provide responses that become almost identical and independent of the conductance of the target at high frequency.

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Section: Horizontal Coplanar Coil Responsessupporting

confidence: 80%

Comparison of Theoretical and Physical Model Studies of the Responses of Moving Source and Fixed Loop Electromagnetic Exploration Systems

Duckworth

2005

Pure appl. geophys.

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“…Subsurface aspects of the tubes and lava streams were monitored by electromagnetic profiling using either the very low frequency (VLF) [McNeill and Labson, 1991] or the EM31 [McNeill, 1980;Frischknecht et al, 1991] technique. Basaltic lava is highly conductive when molten (as much as 2 Siemens/m) and more than 1,000 times less conductive when solidified and cooled to ambient temperature [Rai, 1977;Rai and Manghnani, 1977].…”

Section: And 60% Of Mauna Loa Volcanoes (F Trusdell Written Communimentioning

confidence: 99%

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

Kauahikaua¹,

Cashman²,

Mattox³

et al. 1998

J. Geophys. Res.

215

246

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“…EMI profiling is designed to measure lateral variations in electrical conductivity σ, along a traverse, as opposed to sounding techniques that detect vertical variations in σ with depth (Frischknecht et al, 1991). The most commonly used source for EMI prospecting is a small current-carrying loop, which is essentially a magnetic dipole (West and Macnae, 1991).…”

Section: Introductionmentioning

confidence: 99%

“…Most profiling techniques operate in the frequency domain; however, many acquisition and interpretation procedures are available in the time domain (Nabighian and Macnae, 1991). A significant application of dipolar source EMI profiling is the detection of highly conductive ore bodies for mining, and many instrumentation and interpretation techniques have been developed specifically for this purpose (Frischknecht et al, 1991). EMI profiling for other uses is rapidly increasing for applications such as groundwater, environmental, and engineering studies (see Huang and Won, 2000;Everett, 2013).…”

Section: Introductionmentioning

confidence: 99%

Differentiating tidal and groundwater dynamics from barrier island framework geology: Testing the utility of portable multifrequency electromagnetic induction profilers

et al. 2016

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Electromagnetic induction (EMI) techniques are becoming increasingly popular for near-surface coastal geophysical applications. However, few studies have explored the capabilities and limitations of portable multifrequency EMI profilers for mapping large-scale (10 1 -10 2 km) barrier island hydrogeology. The purpose of this study is to investigate the influence of groundwater dynamics on apparent conductivity σ a to separate the effects of hydrology and geology from the σ a signal. Shorenormal and alongshore surveys were performed within a highly conductive barrier island/wind-tidal flat system at Padre Island National Seashore, Texas, USA. Assessments of instrument calibration and signal drift suggest that σ a measurements are stable, but vary with height and location across the beach. Repeatability tests confirm σ a values using different boom orientations collected during the same day are reproducible. Measurements over a 12 h tidal cycle suggest that there is a tide-dependent step response in σ a , complicating data processing and interpretation. Shore-normal surveys across the barrier/wind-tidal flats show that σ a is roughly negatively correlated with topography and these relationships can be used for characterizing different coastal habitats. For all surveys, σ a increases with decreasing frequency. Alongshore surveys performed during different seasons and beach states reveal a high degree of variability in σ a . Here, it is argued that surveys collected during dry conditions characterize the underlying framework geology, whereas these features are somewhat masked during wet conditions. Differences in EMI signals should be viewed in a relative sense rather than as absolute magnitudes. Small-scale heterogeneities are related to changing hydrology, whereas low-frequency signals at the broadest scales reveal variations in framework geology. Multiple surveys should be done at different times of the year and tidal states before geologic interpretations can confidently be made from EMI surveys in coastal environments. This strategy enables the geophysicist to separate the effects of hydrology and geology from the σ a signal.

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3. Profiling Methods Using Small Sources

Cited by 122 publications

References 0 publications

Comparison of Theoretical and Physical Model Studies of the Responses of Moving Source and Fixed Loop Electromagnetic Exploration Systems

Comparison of Theoretical and Physical Model Studies of the Responses of Moving Source and Fixed Loop Electromagnetic Exploration Systems

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

Differentiating tidal and groundwater dynamics from barrier island framework geology: Testing the utility of portable multifrequency electromagnetic induction profilers

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