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@PHDTHESIS{Zhou:885923,
      author       = {Zhou, Zhen},
      title        = {{E}nhanced crosshole {GPR} full-waveform inversion to
                      improve aquifer characterization},
      volume       = {512},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2020-04179},
      isbn         = {978-3-95806-500-0},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Energie
                      $\&$ Umwelt / Energy $\&$ Environment},
      pages        = {VIII, 136 S.},
      year         = {2020},
      note         = {RWTH Aachen, Diss., 2020},
      abstract     = {Complex heterogeneities in the aquifers are critical and
                      challenging to be detected and can have a significant effect
                      on subsurface flow and transport. Thereby, reliable
                      prediction of groundwater flow and solute transport is
                      important for the protection of drinking water, and the
                      remediation of contaminants. Small-scale high resolution
                      images of the subsurface can help to improve the
                      understanding of complex and heterogeneous aquifer
                      structures that effect hydrological properties and
                      processes. To successfully obtain hydrological parameters
                      distributed in a 2D cross-section with high resolution, we
                      can apply crosshole ground penetrating radar (GPR).
                      Crosshole GPR uses high-frequency electromagnetic pulses
                      that are emitted from a dipole-type antenna in a borehole
                      and recorded by a receiver antenna in a second borehole. The
                      received electromagnetic wave with its arrival time and
                      amplitude contains information about the subsurface medium
                      properties through which it travelled. Thereby, crosshole
                      GPR is able to provide two electromagnetic parameters the
                      dielectric permittivity and the electrical conductivity at
                      the same time. Conventional inversion approaches for
                      crosshole GPR data are generally based on geometrical ray
                      theory, which provide relatively smooth images with a
                      resolution that scales approximately with the diameter of
                      the first Fresnel zone. In contrast, the crosshole GPR
                      full-waveform inversion (FWI) provides decimeter-scalehigh
                      resolution images, because it considers the fully recorded
                      waveform information and the inversion is based on solving
                      the full Maxwell’s equations. However, the crosshole GPR
                      FWI approach also includes some limiting factors and
                      requires several detailed processing and inversion steps. If
                      these steps are not carefully applied, the inversion can be
                      trapped in a local minimum. In order to minimize the
                      influence of at least some of these factors, appreciate FWI
                      starting models and an accurate estimation of the effective
                      source wavelet are required. To precisely describe aquifers,
                      high porosity layers and clay lenses, that can strongly
                      effect flow and transport processes, need to be considered.
                      In the framework of this thesis, we first extend this
                      amplitude analysis approach to identify two different types
                      of low-velocity waveguides, caused by an increased porosity
                      and/or by a higher electrical conductivity. The obtained
                      information about extension and dimension of such wave
                      guiding structures is considered to improve the starting
                      models of the FWI. Moreover, we estimate an updated
                      effective source wavelet based on the updated permittivity
                      starting model. To verify the presented scheme, nine GPR
                      cross-sections were measured and analyzed at the
                      Hermalle-sous-Argenteau test site near Liege in Belgium.
                      Consistent structures between different cross-sections show
                      the robustness of the updated amplitude analysis approach
                      and the FWI results. In addition, the aquifer structures
                      obtained from the new FWI results agree with the crosshole
                      electrical resistivity tomography (ERT) monitoring [...]},
      cin          = {IBG-3},
      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)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/885923},
}