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@ARTICLE{Zhou:890930,
      author       = {Zhou, Zhen and Klotzsche, Anja and Vereecken, Harry},
      title        = {{I}mproving crosshole ground penetrating radar
                      full-waveform inversion results by using progressively
                      expanded bandwidths of the data},
      journal      = {Near surface geophysics},
      volume       = {19},
      number       = {4},
      issn         = {1569-4445},
      address      = {Oxford},
      publisher    = {Wiley},
      reportid     = {FZJ-2021-01255},
      pages        = {465-487},
      year         = {2021},
      abstract     = {In the last decade, time-domain crosshole
                      ground-penetrating radar full-waveform inversion has been
                      applied to several different test sites and has improved the
                      resolution and reconstruction of subsurface properties. The
                      full-waveform inversion requires several diligent executed
                      pre-processing steps to guarantee a successful inversion and
                      to minimize the risk of being trapped in a local minimum.
                      Thereby, one important aspect is the starting models of the
                      full-waveform inversion. Generally, adequate starting models
                      need to fulfil the half-wavelength criterion, which means
                      that the modelled data based on the starting models need to
                      be within half of the wavelength of the measured data in the
                      entire investigation area. Ray-based approaches can provide
                      such starting models, but in the presence of high contrast
                      layers, such results do not always fulfil this criterion and
                      need to be improved and updated. Therefore, precise and
                      detailed data processing and a good understanding of
                      experimental ground-penetrating radar data are necessary to
                      avoid erroneous full-waveform inversion results. Here, we
                      introduce a new approach, which improves the starting model
                      problem and is able to enhance the reconstruction of the
                      subsurface medium properties. The new approach tames the
                      non-linearity issue caused by high contrast complex media,
                      by applying bandpass filters with different passband ranges
                      during the inversion to the modelled and measured
                      ground-penetrating radar data. Thereby, these bandpass
                      filters are considered for a certain number of iterations
                      and are progressively expanded to the selected maximum
                      frequency bandwidth. The resulting permittivity
                      full-waveform inversion model is applied to update the
                      effective source wavelet and is used as an updated starting
                      model in the full-waveform inversion with the full bandwidth
                      data. This full-waveform inversion is able to enhance the
                      reconstruction of the permittivity and electrical
                      conductivity results in contrast to the standard
                      full-waveform inversion results. The new approach has been
                      applied and tested on two synthetic case studies and an
                      experimental data set. The field data were additionally
                      compared with cone penetration test data for validation.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {217 - Für eine nachhaltige Bio-Ökonomie – von
                      Ressourcen zu Produkten (POF4-217) / 2173 -
                      Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217)},
      pid          = {G:(DE-HGF)POF4-217 / G:(DE-HGF)POF4-2173},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000647234500001},
      doi          = {10.1002/nsg.12154},
      url          = {https://juser.fz-juelich.de/record/890930},
}