The use of B-field measurements in an airborne time-domain system: Part I. Benefits of B-field versus<i>dB/dt</i>data

Smith, Richard S.; Annan, Peter

doi:10.1071/eg998024

Cited by 44 publications

(10 citation statements)

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“…This B ‐field response ( B =μH ) is also the electrodynamic ALLTEM response, because its excitation is an integral of a step (triangle wave), it uses d B /d t receivers, and the integral and derivative operations cancel (Smith & Annan 1998). The parametric step response of Smith et al .…”

Section: Methodsmentioning

confidence: 99%

“…This works well for the ALLTEM system because all coils have a square shape, which simplifies the circuital integral using Biot-Savart. The magnetic field at r is the sum of the fields produced by the four straight wire segments, each with current I n , length 2L, and centred at r n , the midpoint of the wire segment (Jackson 1975): This B-field response (B = µH) is also the electrodynamic ALL-TEM response, because its excitation is an integral of a step (triangle wave), it uses dB/dt receivers, and the integral and derivative operations cancel (Smith & Annan 1998). The parametric step response of Smith et al (2004) is a good approximation to the early-time, intermediate-time and late-time portions of the ALLTEM response.…”

Section: Forward Modelmentioning

confidence: 99%

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Hybrid analysis of multiaxis electromagnetic data for discrimination of munitions and explosives of concern

Friedel

Asch

Oden³

2012

Geophysical Journal International

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SUMMARY The remediation of land containing munitions and explosives of concern, otherwise known as unexploded ordnance, is an ongoing problem facing the U.S. Department of Defense and similar agencies worldwide that have used or are transferring training ranges or munitions disposal areas to civilian control. The expense associated with cleanup of land previously used for military training and war provides impetus for research towards enhanced discrimination of buried unexploded ordnance. Towards reducing that expense, a multiaxis electromagnetic induction data collection and software system, called ALLTEM, was designed and tested with support from the U.S. Department of Defense Environmental Security Technology Certification Program. ALLTEM is an on‐time time‐domain system that uses a continuous triangle‐wave excitation to measure the target‐step response rather than traditional impulse response. The system cycles through three orthogonal transmitting loops and records a total of 19 different transmitting and receiving loop combinations with a nominal spatial data sampling interval of 20 cm. Recorded data are pre‐processed and then used in a hybrid discrimination scheme involving both data‐driven and numerical classification techniques. The data‐driven classification scheme is accomplished in three steps. First, field observations are used to train a type of unsupervised artificial neural network, a self‐organizing map (SOM). Second, the SOM is used to simultaneously estimate target parameters (depth, azimuth, inclination, item type and weight) by iterative minimization of the topographic error vectors. Third, the target classification is accomplished by evaluating histograms of the estimated parameters. The numerical classification scheme is also accomplished in three steps. First, the Biot–Savart law is used to model the primary magnetic fields from the transmitter coils and the secondary magnetic fields generated by currents induced in the target materials in the ground. Second, the target response is modelled by three orthogonal dipoles from prolate, oblate and triaxial ellipsoids with one long axis and two shorter axes. Each target consists of all three dipoles. Third, unknown target parameters are determined by comparing modelled to measured target responses. By comparing the rms error among the self‐organizing map and numerical classification results, we achieved greater than 95 per cent detection and correct classification of the munitions and explosives of concern at the direct fire and indirect fire test areas at the UXO Standardized Test Site at the Aberdeen Proving Ground, Maryland in 2010.

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Section: Methodsmentioning

confidence: 99%

Section: Forward Modelmentioning

confidence: 99%

Hybrid analysis of multiaxis electromagnetic data for discrimination of munitions and explosives of concern

Friedel

Asch

Oden³

2012

Geophysical Journal International

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“…In addition, as discussed in Smith and Annan, 1998, the choice of B-field has some further advantages in terms of noisesignal ratio as the B-field is associated with data integration over time that can act as some sort of stacking in time. Clearly, the data stacking can (should) be performed also in the other "direction", that is, spatially, along the line of flight.…”

Section: Airborne Electromagnetic Data (Aem)mentioning

confidence: 99%

New regional stratigraphic insights from a 3D geological model of the Nasia Sub-basin, Ghana, developed for hydrogeological purposes and based on reprocessed B-field data, originally collected for mineral exploration

Dzikunoo¹,

Vignoli²,

Jørgensen³

et al. 2019

Preprint

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Abstract. Re-processing of regional-scale airborne electromagnetic data is used in building a 3D geological model of the Nasia Sub-Basin, Northern Ghana. The resulting 3D geological model consistently integrates all the pieces of information brought by the electromagnetic data, lithologic logs, ground-based geophysical surveys and the prior geological knowledge of the terrain based on previous research. The geo-modelling process is aimed at defining the lithostratigraphy of the area, chiefly to improve the stratigraphic definition of the area as well as for hydrogeological purposes. The airborne electromagnetic measurements, consisting of GEOTEM B-field data, were originally collected for mineral exploration purposes. Thus, those B-field data had to be (re)processed and properly inverted as the original survey and data handling were designed for the detection of potential mineral targets and not for detailed geological mapping. These new geophysical inversion results, compared with the original Conductivity Depth Images, provided a significantly different picture of the subsurface. The new geophysical model led to new interpretations of the geological settings and to the construction of a comprehensive 3D geomodel of the basin. In this respect, the evidences of a hitherto unexposed paleovalley could be inferred from the airborne data. The stratigraphic position of these paleovalleys suggests a distinctly different glaciation history from the Marinoan events, commonly associated with the Kodjari formation of the Voltaian sedimentary basin. Indeed, their presence may be correlated to mountain glaciation within the Sturtian period though no unequivocal glaciogenic strata have yet been identified. This pre-Marinoan glaciation is recorded in rocks of the Wassangara group of the Taoudeni basin. The combination of the Marinoan and, possibly, Sturtian glaciation episodes, both of the Cryogenian period, can be an indication of a Neoproterozoic Snowball Earth. Hence, the occurrence of those geological features, do not only have an important socio-economic consequences – as the paleovalleys can act as reservoirs for groundwater – but, also from a scientific point of view, could be extremely relevant – as their presence would require a revision of the present stratigraphy of the area.

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“…Typically dB/dt data from coils are acquired in TEM surveys. A well-known advantage of B-field data over dB/dt data is that the B-field data have high response at high conductivities, but the dB/dt data do not (Smith, et. al.…”

Section: Comparison Of B and Db/dt Data Inversionmentioning

confidence: 99%

Three-dimensional inversion of SQUID TEM data at Lalor Lake VMS deposit

Yang

Oldenburg

2012

SEG Technical Program Expanded Abstracts 2012

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The combination of high fidelity and late time channels make SQUID magnetometers an attractive sensor for deep and highly conducting targets. Here we focus upon a data set acquired over the Lalor Lake VMS deposit. The deposit consists of a zinc zone between 700m and 1000m depth and a deeper gold/copper zone. The SQUID data set had previously been interpreted using the plate modeling to yield two conductors respectively corresponding to the zinc zone and the gold-copper zone. In this paper we invert these data with our 3D TEM inversion algorithm to produce a 3D voxel conductivity volume. Our 3D model recovers a shallow dipping conductor, which coincides well with the plate model of the zinc zone, as well as a large conductor below 1000m depth. Our inversion is done without incorporating prior knowledge and there is always the potential that large features at depth can be an artifact of the inversion algorithm. To investigate this, and to have confidence, or not, in the existence of the deep body, we carry out a hypothesis analysis where we attempt to find a model that does not have a high conductivity at depth. Forward modeling and subsequent inversion confirms that there must be another conductor below the zinc zone. Much of the concentration of conductivity lies near the region indicated by the initial blind inversion, but the amplitudes and distribution are different. Nevertheless, despite lack of knowledge about geometric details, there is some highly conductive material at depth and it would warrant a drill hole. In a final analysis we look at the relative merits of using B or dB/dt for the particular geometry of this survey. We generate synthetic B and dB/dt data based on our inversion model of Lalor Lake deposit. While the B-field data inversion recovers the correct locations and geometries of the two compact conductors, the dB/dt inversion shows the shallow conductor in a distorted geometry and the deep conductor as a blurred conductive region with conductivity much smaller than the true model. This demonstrates that B-field data can be are superior to dB/dt data for this survey in which we have surface transmitters and receivers.

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The use of B-field measurements in an airborne time-domain system: Part I. Benefits of B-field versusdB/dtdata

Cited by 44 publications

References 1 publication

Hybrid analysis of multiaxis electromagnetic data for discrimination of munitions and explosives of concern

Hybrid analysis of multiaxis electromagnetic data for discrimination of munitions and explosives of concern

New regional stratigraphic insights from a 3D geological model of the Nasia Sub-basin, Ghana, developed for hydrogeological purposes and based on reprocessed B-field data, originally collected for mineral exploration

Three-dimensional inversion of SQUID TEM data at Lalor Lake VMS deposit

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