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@INPROCEEDINGS{Zhao:139387,
      author       = {Zhao, Yulong and Zimmermann, Egon and Huisman, Johan
                      Alexander 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 {EIT} borehole
                      measurements},
      reportid     = {FZJ-2013-05383},
      year         = {2013},
      abstract     = {Spectral Electrical Impedance Tomography (spectral 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
                      because many soils and sediments are only weakly polarizable
                      and show small phase angles between 1 and 20 mrad only. It
                      is a challenge to reach this phase accuracy in a broad
                      frequency range for EIT measurements in the field. In the
                      case of borehole EIT measurements, 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 measured
                      transfer impedances, both coupling effects can cause large
                      phase errors that have typically limited the frequency
                      bandwidth of field EIT measurements to the mHz to Hz range.
                      In this presentation we will i) derive correction procedures
                      for capacitive and inductive coupling effects to extend the
                      applicability of EIT to the kHz range and ii) validate these
                      corrections using controlled laboratory measurements and
                      field measurements. In order to do so, the inductive
                      coupling effect was modeled using electric circuit models
                      and the capacitive coupling effect was modeled by
                      integrating discrete capacitances in the electrical forward
                      model describing the EIT measurement process. The measured
                      calibration data set of mutual inductances obtained for each
                      individual electrode chain was combined with the numerically
                      modeled mutual inductances to obtain the mutual inductance
                      for each considered electrode configuration (e.g.
                      cross-hole). The correction methods were successfully
                      verified with measurements under controlled conditions in a
                      water-filled rain barrel, where a high phase accuracy of 1
                      mrad in the frequency range up to 10 kHz was achieved and
                      also verified in a first field demonstration using a 10 m
                      borehole EIT chain with 8 electrodes. The results of a 1D
                      inversion show that the correction methods increased the
                      phase accuracy considerably.},
      month         = {Mar},
      date          = {2013-03-04},
      organization  = {73. Jahrestagung der Deutschen
                       Geophysikalischen Gesellschaft (DGG),
                       Leipzig (Germany), 4 Mar 2013 - 7 Mar
                       2013},
      cin          = {ZEA-2 / IBG-3},
      cid          = {I:(DE-Juel1)ZEA-2-20090406 / I:(DE-Juel1)IBG-3-20101118},
      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/139387},
}