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@ARTICLE{Zhou:888188,
      author       = {Zhou, Zhen and Klotzsche, Anja and Hermans, Thomas and
                      Nguyen, Frédéric and Schmäck, Jessica and Haruzi, Peleg
                      and Vereecken, Harry and van der Kruk, Jan},
      title        = {3{D} aquifer characterization of the
                      {H}ermalle-sous-{A}rgenteau test site using crosshole
                      ground-penetrating radar amplitude analysis and
                      full-waveform inversion},
      journal      = {Geophysics},
      volume       = {85},
      number       = {6},
      issn         = {1942-2156},
      address      = {Alexandria, Va.},
      publisher    = {GeoScienceWorld},
      reportid     = {FZJ-2020-04750},
      pages        = {H133 - H148},
      year         = {2020},
      abstract     = {To improve the understanding of flow and transport
                      processes in the critical zone, high-resolution and accurate
                      estimation of the small-scale heterogeneity is essential.
                      Preferential flow paths related to high-porosity layers and
                      clay lenses in gravel aquifers greatly affect flow and
                      transport processes in the subsurface, and their high
                      electrical contrast to their surrounding matrix and limited
                      extent can act as low-velocity electromagnetic waveguides.
                      In the past decade, time-domain full-waveform inversion
                      (FWI) of crosshole ground-penetrating radar (GPR) data has
                      shown to provide 2D decimeter-scale resolution images of
                      relative permittivity and electrical conductivity of the
                      subsurface, which can be related to porosity and soil
                      texture. Most studies using crosshole GPR FWI resolved
                      high-porosity zones that were identified by an amplitude
                      analysis approach. But clay lenses or zones with higher
                      electrical conductivity that act as low-velocity waveguides
                      are hard to distinguish in the measured data and amplitude
                      analysis because of the absence of characteristic
                      wave-propagation features. We have investigated a set of
                      nine crosshole GPR data sets from a test site in
                      Hermalle-sous-Argenteau near the Meuse River in Belgium to
                      characterize the aquifer within a decimeter-scale resolution
                      and to improve the understanding of a previously performed
                      heat tracer experiment. Thereby, we extend the amplitude
                      analysis to identify two different types of low-velocity
                      waveguides either caused by an increased porosity or a
                      higher electrical conductivity (and higher porosity).
                      Combining the GPR amplitude analysis for low-velocity
                      waveguide zones with the standard FWI results provided
                      information on waveguide zones, which modified the starting
                      models and further improved the FWI results. Moreover, an
                      updated effective source wavelet is estimated based on the
                      updated permittivity starting models. In comparison with the
                      traditional FWI results, the updated FWI results present
                      smaller gradient of the medium properties and smaller
                      root-mean-squared error values in the final inversion
                      results. The nine crosshole sections are used to generate a
                      3D image of the aquifer and allowed a detailed analysis of
                      the porosity distribution along the different sections.
                      Consistent structures of the permittivity and electrical
                      conductivity show the robustness of the updated FWI results.
                      The aquifer structures obtained by the FWI results agree
                      with those results of the heat tracer experiment.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000618326800023},
      doi          = {10.1190/geo2020-0067.1},
      url          = {https://juser.fz-juelich.de/record/888188},
}