Examples from a new EM and electrical methods receiver system

Duncan, Andrew; Amann, Bill; O’Keeffe, Kristine; Williams, Peter; Tully, Teresa; Wellington, Andrew; Turner, Graham

doi:10.1071/eg998347

Cited by 12 publications

(10 citation statements)

References 1 publication

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“…Full-waveform receivers include the SMARTem (Duncan et al 1998), MIMDAS (Sheard et al 1998) and Zonge GDP-32II systems. They are practical receivers for use in the field as they allow for the acquisition of DHEM and MMR data without the need for mobilization of several different pieces of equipment.…”

Section: Receiver Systemsmentioning

confidence: 99%

“…Conventional receiver systems include the Zonge GDP-16 and GDP-32, Sirotem Mk3, Crone Pulse EM and Geonics Protem. Full-waveform receivers include the SMARTem (Duncan et al 1998), MIMDAS (Sheard et al 1998) and Zonge GDP-32II systems. Several intrinsic features have been built into both types of receiver system to increase the signal/noise ratio of the acquired data.…”

Section: Receiver Systemsmentioning

confidence: 99%

“…Conventional inductive borehole EM methods are used routinely for the location of mineralization off-hole, or the characterization of conductor shape around a conductor intersected by a hole (see, for example, reviews by Asten 1996; Bishop and Lewis 1996). In the vicinity of mine sites, electrical noise from power lines, mine machinery and mine communication equipment becomes a significant problem (Duncan et al 1998). In this paper, data from a series of DHMMR surveys conducted around Broken Hill, New South Wales, Australia, and a borehole EM survey at the Zinkgruvan mine, Sweden, are examined in order to explain the discrepancies observed between different EM receiver systems.…”

Section: Introductionmentioning

confidence: 99%

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A comparison of receiver technologies in borehole MMR and EM surveys

Elders

Asten

2004

Geophysical Prospecting

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A series of downhole magnetometric resistivity (DHMMR) and downhole electromagnetic (DHEM) surveys were conducted near Broken Hill, New South Wales, Australia, and at Zinkgruvan, Sweden, to determine how probe and receiver equipment choices affect the amount of noise visible in borehole MMR and EM data. Noise analyses performed on the data, using the standard deviation to gauge the relative noise levels between different probes and receiver systems, indicate that high noise levels in MMR data result primarily from the use of a three‐component EM probe, which has a reduced effective area and hence a higher noise floor compared with a single‐component EM probe. High noise, attributable to cultural sources such as nearby power lines, in either MMR or EM data can be reduced through the use of full‐waveform, multipurpose receiver systems. These systems allow for the use of tapered stacking, which is a more effective method of eliminating coherent noise associated with power‐line transients than the boxcar‐stacking method used by traditional receiver systems.

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Section: Receiver Systemsmentioning

confidence: 99%

Section: Receiver Systemsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A comparison of receiver technologies in borehole MMR and EM surveys

Elders

Asten

2004

Geophysical Prospecting

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“…Until the mid-1980s, axial induction coil sensors were commonly used. However, the added value of 3C measurements led to development of 3C magnetic field sensors (e.g., Pantze et al 1986;Cull 1996a, b;Hughes and Ravenhurst 1996;Duncan et al 1998;Elders and Asten 2004). Simultaneously, receiver systems were improved, and modern instruments have enhanced filtering and stacking capability for derivation of processed data in the field and the recording of raw time series for advanced processing in the laboratory (e.g., Duncan et al 1998;Elders and Asten 2004).…”

Section: Other Borehole Electromagnetic Methodsmentioning

confidence: 99%

“…Owing to space limitations in the borehole probe in the off-axial directions, induction coils cannot reach a sensitivity level acceptable for AMT measurements in the off-axial directions of boreholes. For the controlled-source BHEM methods, 3C borehole induction magnetometers are used on a routine basis (e.g., Pantze et al 1986;Cull 1996a, b;Duncan et al 1998;Elders and Asten 2004). Even though signal levels generated by BHEM sources are typically higher than those of AMT, the two off-axial components of the BHEM magnetic field are still problematic with respect to noise.…”

Section: Borehole Sensors and Conditionsmentioning

confidence: 99%

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Kalscheuer

Juhojuntti

Vaittinen³

2017

Surv Geophys

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A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $ 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and elect...

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A matlab-based frequency-domain electromagnetic inversion code (FEMIC) with graphical user interface

Elwaseif¹,

Robinson²,

Day‐Lewis³

et al. 2017

Computers & Geosciences

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We present a new Matlab-based 1 frequency-domain electromagnetic (EM) inversion code (FEMIC) for analysis of datasets collected using multi-frequency EM-induction instruments. The code includes routines for data filtering and calibration, forward modeling, inverse modeling, image appraisal (i.e., calculation of the depth of investigation), and visualization. A one-dimensional forward model is assumed, but two or three dimensional lateral regularization constraints can be applied during the inversion. The code can take advantage of the parallel-processing capabilities of multi-processor computers, thus facilitating efficient inversion of large datasets. Synthetic and field examples demonstrate the operation of the FEMIC code and showcase its capabilities. Source code is provided as material supplementary to this paper to allow modifications and extensions by others.

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Examples from a new EM and electrical methods receiver system

Cited by 12 publications

References 1 publication

A comparison of receiver technologies in borehole MMR and EM surveys

A comparison of receiver technologies in borehole MMR and EM surveys

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

A matlab-based frequency-domain electromagnetic inversion code (FEMIC) with graphical user interface

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