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@ARTICLE{Zhao:135068,
      author       = {Zhao, Y and Zimmermann, Egon and Huisman, J A and Treichel,
                      A and Wolters, Bernd and van Waasen, S and Kemna, A.},
      title        = {{B}roadband {EIT} borehole measurements with high phase
                      accuracy using numerical corrections of electromagnetic
                      coupling effects},
      journal      = {Measurement science and technology},
      volume       = {24},
      number       = {8},
      issn         = {1361-6501},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {FZJ-2013-03056},
      pages        = {085005 -},
      year         = {2013},
      abstract     = {Electrical impedance tomography (EIT) is gaining importance
                      in the field of geophysics and there is increasing interest
                      for accurate borehole EIT measurements in a broad frequency
                      range (mHz to kHz) in order to study subsurface properties.
                      To characterize weakly polarizable soils and sediments with
                      EIT, high phase accuracy is required. Typically, long
                      electrode cables are used for borehole measurements.
                      However, this may lead to undesired electromagnetic coupling
                      effects associated with inductive coupling between the
                      double wire pairs for current injection and potential
                      measurement and capacitive coupling between the electrically
                      conductive shield of the cable and the electrically
                      conductive environment surrounding the electrode cables.
                      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 measurements to the mHz to
                      Hz range. The aim of this paper is to develop numerical
                      corrections for these phase errors. To this end, 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 0.8
                      mrad in the frequency range up to 10 kHz was achieved. The
                      corrections were also applied to field EIT measurements made
                      using a 25 m long EIT borehole chain with 8 electrodes and
                      an electrode separation of 1 m. The results of a 1D
                      inversion of these measurements showed that the correction
                      methods increased the measurement accuracy considerably. It
                      was concluded that the proposed correction methods enlarge
                      the bandwidth of the field EIT measurement system, and that
                      accurate EIT measurements can now be made in the mHz to kHz
                      frequency range. This increased accuracy in the kHz range
                      will allow a more accurate field characterization of the
                      complex electrical conductivity of soils and sediments,
                      which may lead to improved estimation of saturated hydraulic
                      conductivity from electrical properties. Although the
                      correction methods have been developed for a custom-made EIT
                      system, they also have potential to improve to the phase
                      accuracy of EIT measurements made with commercial systems
                      relying on multicore cables.},
      cin          = {ZEA-2 / IBG-3},
      ddc          = {600},
      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)16},
      UT           = {WOS:000321943100014},
      doi          = {10.1088/0957-0233/24/8/085005},
      url          = {https://juser.fz-juelich.de/record/135068},
}