GEM‐2: A New Multifrequency Electromagnetic Sensor

Won, I. J.; Keiswetter, Dean; Fields, George R. A.; Sutton, Lynn C.

doi:10.4133/jeeg1.2.129

Cited by 153 publications

(89 citation statements)

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“…Portable multifrequency EMI profilers provide users with the flexibility of choosing between several operating frequencies, as well as varying the instrument's orientation, height, and coil configuration (Won et al, 1996;Huang et al, 2008). Unless otherwise mentioned, "portable" means a lightweight sensor that is used by one person and can be operated in a continuous acquisition mode while walking.…”

Section: Portable Multifrequency Emi Systemsmentioning

confidence: 99%

“…For example, the GSSI Profiler EMP-400™ contains a TX coil that continuously emits a waveform containing multiple frequencies within 1-16 kHz bandwidth, selectable at 1 kHz increments (Geophysical Survey Systems Incorporated [GSSI], 2007;Huang et al, 2008). The RX coil measures the in-phase I and the quadrature (out-of-phase) Q components of the time derivative of the secondary magnetic field (Won et al, 1996). The configuration of the GSSI Profiler EMP-400 and an example of its use in the field is shown in Figure 1a.…”

Section: Portable Multifrequency Emi Systemsmentioning

confidence: 99%

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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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Section: Portable Multifrequency Emi Systemsmentioning

confidence: 99%

Section: Portable Multifrequency Emi Systemsmentioning

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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“…The GEM-2 is a hand-held, digital, multi-fiequency electromagnetic sensor operating over a fkequency band of 90 Hz to 23 kHz (Won et al, 1996). The unit is capable of transmitting and receiving any digitally synthesized waveform by means of the pulse-width modulation technique.…”

Section: Gem-2 Instrument Descriptionmentioning

confidence: 99%

Final report on passive and active low-frequency electromagnetic spectroscopy for airborne detection of underground facilities

SanFilipo¹

2000

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DISUAIMERThe vertical component of the magnetic field generated by a thee-phase Executive SummaryElectromagnetic (EM) induction techniques can potentially provide information that will contribute to the delineation and characterization of Underground Facilities (UGF) which produce weapons of mass destruction or perform other covert activities deemed threatening to our national security. EM geophysical techniques, used widely in mineral exploration, geohydrology, engineering, and environmental assessment, consists of measurements of fluctuating magnetic fields with a loop antenna at the surface of the earth above or in a bore hole near the subsurkce target area. The fluctuating fields may be natural (magnetotellurics), excited by a controlled source which is part of the EM instrumentation (active EM), or emitted by an electrically active target (passive EM). Active EM provides information about the conductivity andor permeability distribution in the subsurface resulting fkom the scattering of the primary field emitted fiom the active EM transmitter by the anomalous zones, fiom induced eddy currents in highly conductive targets, magnetic polarition of permeable targets, perturbation of background current flow in a conductive earth, or a combination of these phenomena. The conductivity and permeability distribution may be associated with man-made structures that include metal and voids which, in turn, may be an element of a UGF. Passive EM provides a means of directly sensing the operation of electrical equipment or of power lines feeding them,with the potential to both locate the equipment or power lines fiom spatially sampled data and characterize the equipment &om the spectral content of the EM signal.The objective'of the research performed under this project was to advance EM induction sensor technology and software for modeling and interpreting EM induction data, and perform experiments testing EM methodology pertaining to UGF.Hardware development primarily focused on improvements to the GEM-2 instruments, including changes that have been implemented in operational units that have been built, as well as design and module prototyping for the next generation. We also have experimented with new sensor calibration techniques. 'An undertaking to derive more rigorous imaging algorithms for active source EM data has been the focus of software research efforts. In an attempt to achieve a practical compromise between the simple, crude Born approximation and the very complex rigorous solution of Maxwell's equations for the general three-dimensional scattering problem, an inversion algorithm based on the "extended Born" approximation has been developed. This scheme accounts for the field alteration generated by the conductivity anomaly in an approximate way that eliminates the need to solve a large matrix equation. The approximation is based on the assumption that the variation of the electric field in the anomalous region is small, which, unfortunately, is not always the case. Efforts to improve the approxi...

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“…Currently, commercial products mainly include EM31-MK2, EM34-3, EM38 by Geonics [5,6], GEM-2, GEM-3, GEM-5 by Geophex [7][8][9] and Russian NEMFIS [3] system. Based on geometric sounding principle, EM series systems made by Geonics can achieve different depth sounding by changing the distance between transmitter and receiver and the corresponding operating frequency.…”

Section: Introductionmentioning

confidence: 99%

A Portable Frequency Domain Electromagnetic System for Shallow Metal Targets Detection

Qu¹,

Li²,

Fang³

et al. 2017

PIER M

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Abstract-In this paper, a portable frequency domain electromagnetic system CEM-2 is presented for shallow metal targets detection. This paper discusses the detection principle of frequency domain electromagnetic system, introduces hardware implementation, presents test results of each module, and gives the system's imaging results in field tests. Sinusoidal pulse width modulation technique is employed in this system to produce single-frequency or multi-frequencies synthetic electromagnetic signals with signal to noise ratio of about 85 dB. After integration, the CEM-2 system's in-phase noise level is about 90 ppm while the quadrature response is about 100 ppm. The experiment results of CEM-2 agree well with the simulation ones both from signatures and amplitudes. The experiment for detecting targets of different sizes and materials conducted in field indicates that CEM-2 system can be used to distinguish metallic and ferrous objects.

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GEM‐2: A New Multifrequency Electromagnetic Sensor

Cited by 153 publications

References 0 publications

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

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

Final report on passive and active low-frequency electromagnetic spectroscopy for airborne detection of underground facilities

A Portable Frequency Domain Electromagnetic System for Shallow Metal Targets Detection

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