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On the Use of Electromagnetics for Earth Imaging of the Polar Regions.

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Title: On the Use of Electromagnetics for Earth Imaging of the Polar Regions.
Authors: Hill, Graham J.1,2 (AUTHOR) gjhill@ig.cas.cz
Source: Surveys in Geophysics. Jan2020, Vol. 41 Issue 1, p5-45. 41p.
Subject Terms: *Electric field strength, *Electromagnetism, *Earth currents, *Electric noise, *Glacial landforms, *Snow cover, *Geophysics
Geographic Terms: Antarctica
Abstract: The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts. (2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of 'blizstatic', localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s−1, the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions. [ABSTRACT FROM AUTHOR]
Database: Energy & Power Source
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  Data: On the Use of Electromagnetics for Earth Imaging of the Polar Regions.
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  Data: <searchLink fieldCode="JN" term="%22Surveys+in+Geophysics%22">Surveys in Geophysics</searchLink>. Jan2020, Vol. 41 Issue 1, p5-45. 41p.
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  Data: *<searchLink fieldCode="DE" term="%22Electric+field+strength%22">Electric field strength</searchLink><br />*<searchLink fieldCode="DE" term="%22Electromagnetism%22">Electromagnetism</searchLink><br />*<searchLink fieldCode="DE" term="%22Earth+currents%22">Earth currents</searchLink><br />*<searchLink fieldCode="DE" term="%22Electric+noise%22">Electric noise</searchLink><br />*<searchLink fieldCode="DE" term="%22Glacial+landforms%22">Glacial landforms</searchLink><br />*<searchLink fieldCode="DE" term="%22Snow+cover%22">Snow cover</searchLink><br />*<searchLink fieldCode="DE" term="%22Geophysics%22">Geophysics</searchLink>
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  Data: <searchLink fieldCode="DE" term="%22Antarctica%22">Antarctica</searchLink>
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  Label: Abstract
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  Data: The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts. (2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of 'blizstatic', localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s−1, the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions. [ABSTRACT FROM AUTHOR]
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      – Type: doi
        Value: 10.1007/s10712-019-09570-8
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      – Code: eng
        Text: English
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        PageCount: 41
        StartPage: 5
    Subjects:
      – SubjectFull: Electric field strength
        Type: general
      – SubjectFull: Electromagnetism
        Type: general
      – SubjectFull: Earth currents
        Type: general
      – SubjectFull: Electric noise
        Type: general
      – SubjectFull: Glacial landforms
        Type: general
      – SubjectFull: Snow cover
        Type: general
      – SubjectFull: Geophysics
        Type: general
      – SubjectFull: Antarctica
        Type: general
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      – TitleFull: On the Use of Electromagnetics for Earth Imaging of the Polar Regions.
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              M: 01
              Text: Jan2020
              Type: published
              Y: 2020
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            – TitleFull: Surveys in Geophysics
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