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@INPROCEEDINGS{Zhao:128678,
      author       = {Zhao, Yulong and Zimmermann, Egon and Huisman, J.A.
                      (Sander) and Treichel, Andrea and Wolters, Bernd and van
                      Waasen, Stefan and Kemna, A.},
      title        = {{N}umerical correction of the phase error due to
                      electromagnetic coupling effects in 1{D} {EIT} borehole
                      measurements},
      school       = {university of Bonn},
      reportid     = {FZJ-2013-00412},
      year         = {2012},
      abstract     = {Spectral Electrical Impedance Tomography (EIT) allows
                      obtaining images of the complex electrical conductivity for
                      a broad frequency range (mHz to kHz). It has recently
                      received increased interest in the field of near-surface
                      geophysics and hydrogeophysics because of the relationships
                      between complex electrical properties and hydrogeological
                      and biogeochemical properties and processes observed in the
                      laboratory with Spectral Induced Polarization (SIP).
                      However, these laboratory results have also indicated that a
                      high phase accuracy is required for surface and borehole EIT
                      measurements because many soils and sediments are only
                      weakly polarizable and show phase angles between 1 and 20
                      mrad. In the case of borehole EIT measurements, long cables
                      and electrode chains (>10 meters) are typically used, which
                      leads to undesired inductive coupling between the electric
                      loops for current injection and potential measurement and
                      capacitive coupling between the electrically conductive
                      cable shielding and the soil. Depending on the electrical
                      properties of the subsurface and the measured transfer
                      impedances, both coupling effects can cause large phase
                      errors that have typically limited the frequency bandwidth
                      of field EIT measurement to the mHz to Hz range. The aim of
                      this study is i) to develop correction procedures for these
                      coupling effects to extend the applicability of EIT to the
                      kHz range and ii) to validate these corrections using
                      controlled laboratory measurements and field measurements.
                      In order to do so, the inductive coupling effect was modeled
                      using electronic circuit models and the capacitive coupling
                      effect was modeled by integrating discrete capacitances in
                      the electrical forward model describing the EIT measurement
                      process. The correction methods were successfully verified
                      with measurements under controlled conditions in a
                      water-filled rain barrel, where a high phase accuracy of 2
                      mrad in the frequency range up to 10 kHz was achieved. In a
                      field demonstration using a 10 m borehole EIT chain with 8
                      electrodes with 1 m electrode separation, the corrections
                      were also applied within a 1D inversion of the borehole EIT
                      measurements. The results show that the correction methods
                      increased the measurement accuracy considerably.},
      month         = {Dec},
      date          = {2012-12-03},
      organization  = {American Geophysical Union’s 45th
                       annual Fall Meeting, San Francisco
                       (USA), 3 Dec 2012 - 7 Dec 2012},
      subtyp        = {After Call},
      cin          = {ZEA-2},
      cid          = {I:(DE-Juel1)ZEA-2-20090406},
      pnm          = {246 - Modelling and Monitoring Terrestrial Systems: Methods
                      and Technologies (POF2-246)},
      pid          = {G:(DE-HGF)POF2-246},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/128678},
}