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@ARTICLE{Mozaffari:894879,
      author       = {Mozaffari, Amirpasha and Klotzsche, Anja and Zhou, Zhen and
                      Vereecken, Harry and van der Kruk, Jan},
      title        = {3-{D} {E}lectromagnetic {M}odeling {E}xplains
                      {A}pparent-{V}elocity {I}ncrease in {C}rosshole {GPR}
                      {D}ata-{B}orehole {F}luid {E}ffect {C}orrection {M}ethod
                      {E}nables to {I}ncorporating {H}igh-{A}ngle {T}raveltime
                      {D}ata},
      journal      = {IEEE transactions on geoscience and remote sensing},
      volume       = {60},
      issn         = {0018-9413},
      address      = {New York, NY},
      publisher    = {IEEE},
      reportid     = {FZJ-2021-03450},
      pages        = {1 - 10, Art no. 5905710},
      year         = {2022},
      abstract     = {For high-resolution crosshole ground-penetrating radar
                      (GPR) tomography, a wide-range of ray path angles are
                      required, including transmitter-receiver pairs with
                      high-angles. However, artefacts have been observed in the
                      inverted GPR tomograms when high-angle data were
                      incorporated in ray-based inversion (RBI) tomography, due to
                      not well-understood increasing apparent velocities for
                      increasing ray-angles. To reduce these artefacts, it is
                      common practice to limit the angular aperture to a threshold
                      between 30° to 50°, which reduces the spatial resolution.
                      We apply 3D finite-difference time-domain GPR modelling
                      including borehole fluid and resistive loaded finite-length
                      antenna models to study the increase of apparent velocity
                      with increasing ray path angle. This study shows that the
                      strong refraction of the electromagnetic waves at the
                      borehole interface between water and subsurface is one of
                      the reasons for these not well-understood phenomena. We
                      introduce a novel borehole-fluid effect correction (BFEC)
                      that relocates the transmitter and receiver positions to the
                      location where the refraction is occurring to remove any
                      influence of the borehole such that the remaining
                      traveltimes can be inverted using an RBI. BFEC improves the
                      estimated apparent-velocity (relative permittivity) values
                      and enables the incorporation of wide-angle ray paths
                      resulting in more accurate tomograms. We verify the BFEC for
                      a homogenous and realistic synthetic model. By applying
                      curved-ray RBI without and with the BFEC, the subsurface
                      structures are reconstructed with more details for the BFEC
                      data and average relative error model reduced from $13\%$ to
                      under $9\%$ for the high-resolution inhomogeneous model.},
      cin          = {JSC / IBG-3},
      ddc          = {620},
      cid          = {I:(DE-Juel1)JSC-20090406 / I:(DE-Juel1)IBG-3-20101118},
      pnm          = {2173 - Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217) / 5111 - Domain-Specific Simulation $\&$ Data
                      Life Cycle Labs (SDLs) and Research Groups (POF4-511) /
                      Earth System Data Exploration (ESDE)},
      pid          = {G:(DE-HGF)POF4-2173 / G:(DE-HGF)POF4-5111 /
                      G:(DE-Juel-1)ESDE},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000732750600001},
      doi          = {10.1109/TGRS.2021.3107451},
      url          = {https://juser.fz-juelich.de/record/894879},
}