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@ARTICLE{Keskinen:902657,
      author       = {Keskinen, Johanna and Looms, Majken C. and Klotzsche, Anja
                      and Nielsen, Lars},
      title        = {{P}ractical data acquisition strategy for time-lapse
                      experiments using crosshole {GPR} and full-waveform
                      inversion},
      journal      = {Journal of applied geophysics},
      volume       = {191},
      issn         = {0926-9851},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2021-04444},
      pages        = {104362 -},
      year         = {2021},
      abstract     = {Crosshole ground penetrating radar (GPR) methods are
                      increasingly used in time-lapse studies of flow in the
                      uppermost near subsurface with important implications for
                      our understanding of e.g., water infiltration in the
                      unsaturated zone, and fluid flow in the saturated zone. A
                      particular challenge in such time-lapse crosshole studies is
                      the trade-off between collecting sufficient data to be able
                      to resolve how a tracer moves, and, minimizing the data
                      acquisition time such that the data approximates a static
                      state. We test how dense recording geometries are needed for
                      resolving a gas bubble injected in a highly heterogeneous
                      chalk reservoir analogue using a full-waveform inversion
                      (FWI) approach for modelling the crosshole GPR data. We show
                      that even relatively sparse geometries provide sufficient
                      resolution of the permittivity contrast caused by the gas
                      bubble, provided that the detailed background permittivity
                      structure is known from prior (before gas injection) FWI
                      analysis of densely recorded high-resolution data. The
                      conductivity contrast caused by the gas is more challenging
                      to recover and the resolution suffers to a higher degree
                      when reducing the survey geometry or at higher noise levels.
                      As long as the permittivity change during the time-lapse
                      experiment is the main target, a significant reduction in
                      acquisition time is therefore possible as compared to the
                      time needed to record the background permittivity structure.
                      This reduced acquisition time has important practical
                      implications for time-lapse experiments under realistic
                      conditions. Our results are based on synthetic analysis
                      based on a realistic subsurface scenario closely linked to
                      characterization of heterogeneous chalk reservoirs. However,
                      our findings also have important implications for planning
                      of future time-lapse studies in other settings.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {2173 - Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2173},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000662834300010},
      doi          = {10.1016/j.jappgeo.2021.104362},
      url          = {https://juser.fz-juelich.de/record/902657},
}