Airborne EM surveys applied to environmental mapping in the UK

Beamish, David; Mattsson, A.; Kurimo, M.

doi:10.3997/2214-4609.201406304

Cited by 6 publications

(4 citation statements)

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“…The airborne electromagnetic (AEM) data is acquired at four frequencies and the highest frequency provides information on the bulk electrical conductivities of near-surface formations. Due to their sensitivity to enhanced pore-fluid conductivities, the data have been used in a wide-range of localised environmental investigations in relation to industrial sites, coal-mine spoil and both open and closed landfills (Beamish, 2002(Beamish, , 2003. The impact of colliery spoil zones across the Permo-Triassic aquifer of Nottinghamshire has been described by Beamish & Klinck (2006).…”

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Mapping and predicting electrical conductivity variations across southern England using airborne electromagnetic data

Beamish

White

2012

QJEGH

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Electrical conductivity of is one of the fundamental geophysical properties of rock formations and can be measured at field and laboratory scales. A recent airborne geophysical survey of the Isle of Wight and part of the adjacent mainland has provided an assessment of the nearsurface (close to outcrop) electrical conductivities associated with Palaeogene and Cretaceous formations. This study examines the degree to which the high resolution survey data contain distinctive geological and lithological signatures. The geostatistical nature of the conductivity distributions are examined in relation to two existing sedimentary bedrock schemes involving lithostratigraphical and simpler lithological descriptions. A close association between conductivity and bedrock geology is evident. It is then demonstrated how the central moments and dispersion statistics of the distributions may be used to predict the continuous, bedrock conductivity distribution across a large area of southern England, containing, as it does, a high population density and extensive infrastructure. The effectiveness of the method is demonstrated using the survey data obtained on the mainland and an existing database of Vertical Electric Soundings. Page 3 of 34The electrical properties of UK soils and rocks were investigated during the 1930s in both the laboratory and using geophysical field measurements. These early measurements were intended to provide a framework for understanding the potential impact of ground conductivity on the then developing radio and telephone transmission systems. The laboratory experiments, typically using 'soil' samples to depths of about 3 m, are described by Smith-Rose (1933, 1935 During the latter half of the last century more routine electrical and electromagnetic geophysical measurements provided a wealth of localised survey information for a variety of applications across the UK. Many of the measurements comprised vertical electric soundings (VES) for groundwater applications. The National Resistivity Sounding Database (Barker et al., 1996) was developed from over 8,000 such soundings. The database information, comprising raw resistances, continues to be used in a geological context (Cuthbert et al., 2009;Busby et al., 2011). Electromagnetic measurements have also been used to guide geological mapping, usually in the near-surface (e.g. Zalasiewicz et al., 1985;Cornwell & Carruthers, 1986) Having established the statistical behaviour of the near-surface conductivity of the geological units across the IoW, the ability of these data to perform predictive mapping across a large central area of southern England is considered. The effectiveness of this procedure is demonstrated using both survey data obtained on the mainland and an existing database of Vertical Electric Soundings. The extended bedrock conductivity map has the potential to allow assessments of the degree to which localised measurements are consistent with, or represent departures from, the norm. The GIS-based predictive mapping of geophysical inf...

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Mapping and predicting electrical conductivity variations across southern England using airborne electromagnetic data

Beamish

White

2012

QJEGH

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“…(2000a,b). Environmental applications of the high‐resolution geophysical data sets in the UK are discussed by Beamish (2002) and Peart et al. (2003).…”

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Hydrochemical characterization of a coal mine plume detected by an airborne geophysical survey

Beamish¹,

Klinck²

2006

Geofluids

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A trial airborne electromagnetic (AEM) geophysical survey was carried out across a 13 x 9 km area of the northern Nottinghamshire (UK) coalfield. One of the objectives was to examine the influence of coal mines (collieries) and associated spoil heaps situated above the Triassic Sherwood Sandstone aquifer. The conductivity models obtained from the AEM survey revealed extensive zones of enhanced subsurface conductivity in the vicinity of all the collieries in the survey area. The present study provides information regarding subsequent investigations (ground geophysics and borehole) to confirm the AEM results and to investigate the geochemical nature of the conductive zone identified in the vicinity of one of the collieries.Following ground geophysical confirmation of the airborne results, three boreholes were drilled into one of the conductive zones to the east of a working colliery. Geophysical logs and analysis of pore fluid geochemistry demonstrate that there is a very strong correlation between the borehole induction logs (formation conductivity), total dissolved solids and chloride in the pore waters. The three, cored boreholes have confirmed that there is a groundwater plume with high concentrations of total dissolved solids, compared to background, moving east from the Thoresby Colliery on a hydraulic gradient of 0.023. Porewater geochemistry obtained from core has been compared with that of local aquifer waters and with samples obtained from the colliery. The results indicate that the plume chemistry could result from the mixing of a typical Sherwood Sandstone composition with colliery spoil leachate. The AEM conductivity models have been successfully correlated with ground geophysical models, borehole induction logs, total dissolved solids and chloride in the pore waters. By implication, the geophysical results obtained over a larger area indicate the wider extent of such impacts in relation to both former and current mining activities.

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“…Airborne electromagnetic (AEM) measurements, traditionally used for mineral exploration, are increasingly being applied to a variety of near‐surface uses. Recent applications of frequency‐domain AEM include infrastructure (Beard and Lutro 2000), groundwater vulnerability (Fitterman and Deszcz‐Pan 1998), environmental surveys (Jokinen and Lanne 1996; Beamish and Kurimo 2000; Doll et al . 2000) and Quaternary and surficial geological mapping (Puranen et al .…”

Section: Introductionmentioning

confidence: 99%

Airborne EM footprints

Beamish¹

2003

Geophysical Prospecting

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As frequency domain airborne electromagnetic studies (AEM) move towards more detailed assessments of the near surface, the behaviour of system footprints, and hence the spatial averages involved in the measurement, becomes important.Published estimates suffer from two main limitations; firstly they are based on perfectly conducting, thin sheet models and, secondly, they are system specific. The present study is a revision of footprint estimates based on (i) a finitely conducting half-space and (ii) an at-surface scale estimate that uses the spatial equivalent of the conventional electromagnetic skin depth.In order to remove the system dependence, a transmitter footprint is defined in terms of electromagnetic skin distance. Only the limiting cases of vertical and horizontal magnetic dipole sources then require analysis. Electromagnetic skin distances, two for each of the coil orientations, are defined. The revised definition makes it possible to investigate the footprint behaviour of both towed-bird and fixed-wing AEM systems over an altitude range from 20 to 100 m. The footprint/altitude ratio has a primary dependence on altitude and a secondary dependence on both resistivity and frequency. The analysis covers a frequency range from 1 to 100 kHz and results are presented for two specific resistivity values that represent conductive (10 m) and resistive (1000 m) environments.The revised footprint parameters display a quasi-linear behaviour with altitude, particularly for mid-range frequencies. This behaviour enables the coefficients of linear, least-squares relationships to be obtained thus assisting with the prediction of footprint estimates for survey planning and interpretation. A comparison of the new estimates with published values suggests that existing footprint values for a vertical magnetic dipole should be revised downward.3

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Airborne EM surveys applied to environmental mapping in the UK

Cited by 6 publications

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Mapping and predicting electrical conductivity variations across southern England using airborne electromagnetic data

Mapping and predicting electrical conductivity variations across southern England using airborne electromagnetic data

Hydrochemical characterization of a coal mine plume detected by an airborne geophysical survey

Airborne EM footprints

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