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@ARTICLE{Mangel:203156,
      author       = {Mangel, Adam R. and Moysey, Stephen M. J. and van der Kruk,
                      Jan},
      title        = {{R}esolving precipitation induced water content profiles by
                      inversion of dispersive {GPR} data: {A} numerical study},
      journal      = {Journal of hydrology},
      volume       = {525},
      issn         = {0022-1694},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2015-05161},
      pages        = {496 - 505},
      year         = {2015},
      abstract     = {Surface-based ground-penetrating radar (GPR) measurements
                      have significant potential for monitoring dynamic hydrologic
                      processes at multiple scales in time and space. At early
                      times during infiltration into a soil, the zone above the
                      wetting front may act as a low-velocity waveguide that traps
                      GPR waves, thereby causing dispersion and making
                      interpretation of the data using standard methods difficult.
                      In this work, we show that the dispersion is dependent upon
                      the distribution of water within the waveguide, which is
                      controlled by soil hydrologic properties. Simulations of
                      infiltration were performed by varying the n-parameter of
                      the Mualem–van Genuchten equation using HYDRUS-1D; the
                      associated GPR data were simulated to evaluate the influence
                      of dispersion. We observed a notable decrease in wave
                      dispersion as the sharpness of the wetting front profile
                      decreased. Given the sensitivity of the dispersion effect to
                      the wetting front profile, we also evaluated whether the
                      water content distribution can be determined through
                      inversion of the dispersive GPR data. We found that a global
                      grid search combined with the simplex algorithm was able to
                      estimate the average water content when the wetted zone is
                      divided into 2 layers. This approach was incapable, however,
                      of representing the gradational nature of the water content
                      distribution behind the wetting front. In contrast, the
                      shuffled complex evolution algorithm was able to constrain a
                      piece-wise linear function to closely match the shallow
                      gradational water content profile. In both the layered and
                      piece-wise linear case, the sensitivity of the dispersive
                      data dropped sharply below the wetting front, which in this
                      case was around 20 cm, i.e., twice the average wavelength,
                      for a 900 MHz GPR survey. This study demonstrates that
                      dispersive GPR data has significant potential for capturing
                      the early-time dynamics of infiltration that cannot be
                      obtained with standard GPR analysis approaches.},
      cin          = {IBG-3},
      ddc          = {690},
      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:000355885600042},
      doi          = {10.1016/j.jhydrol.2015.04.011},
      url          = {https://juser.fz-juelich.de/record/203156},
}