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@PHDTHESIS{Mboh:133236,
      author       = {Mboh, Cho Miltin},
      title        = {{C}oupled {H}ydrogeophysical inversion for soil hydraulic
                      property estimation from time-lapse geophysical data},
      volume       = {154},
      school       = {Universität Bonn},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2013-01774},
      isbn         = {978-3-89336-823-5},
      series       = {Schriften des Forschungszentrums Jülich : Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {79 p.},
      year         = {2012},
      note         = {Universität Bonn, Diss., 2012},
      abstract     = {Good knowledge of the hydraulic properties of the vadose
                      zone is important for understanding water flow and solute
                      transport processes therein. This can help to promote
                      sustainable use and mitigate anthropogenic threats to soil
                      and water resources. The use of time-lapse geophysical data
                      to constrain our understanding of the flow and transport
                      properties of the vadose zone is now well recognised.
                      Conventional use of geophysical data to estimate the
                      hydraulic properties of the vadose zone is based on an
                      uncoupled inversion approach including an ill-posed
                      tomograhic inversion step which can lead to error
                      propagation to the estimated hydraulic properties. One way
                      of improving the accuracy of estimating soil hydraulic
                      properties is to use a so-called coupled hydrogeophysical
                      inversion approach. In this inversion approach, the
                      tomograhic inversion step is avoided as geophysical
                      measurements are directly used in the hydrological inverse
                      problem by coupling a forward model of the geophysical
                      measurements with a hydrological model describing the
                      hydrologic processes under investigation. Although the
                      potential benefits of the coupled inversion approach have
                      been illustrated with synthetic data, there are very few
                      applications of the approach to actual field or laboratory
                      data. Moreover, most studies using this approach focused on
                      electrical resistivity tomography (ERT) and ground
                      penetration radar (GPR), and the usefulness of this
                      inversion approach remains to be explored for a range of
                      other geophysical methods. Although coupled hydrogeophysical
                      inversion frameworks are flexible enough for the integration
                      of multiple hydrologic and geophysical data types, this data
                      fusion aspect has also received less attention. Therefore,
                      the aim of this thesis was to develop inversion frameworks
                      for the estimation of effective subsurface hydraulic
                      parameters from: i) the fusion of ERT and inflow data
                      obtained under constant head infiltration in a field sandy
                      loam, ii) SP data acquired during primary drainage of a
                      sandy soil column, and iii) TDR data obtained under falling
                      head infiltration into an initially dry sandy loam. Based on
                      synthetic and actual data we showed that it is feasible to
                      estimate three key Mualem-van Genuchten parameters (α, n
                      and Ks), using the developed coupled hydrogeophysical
                      inversion frameworks for ERT, SP and TDR. In all cases, the
                      inversion results compared well with independently obtained
                      values. With respect to the fusion of ERT and inflow data,
                      it was observed that the success of the procedure depends on
                      the choice of an appropriate objective function. The best
                      results were obtained when an objective function defined as
                      the sum of the root mean square error of both data types
                      normalized by the standard deviation of the respective
                      measurements was used. On the other hand, successful
                      inversion of the SP data depended on efficient pre-treatment
                      of the measured signals prior to inversion and the
                      availability of an adequate model for the voltage coupling
                      coefficient at partial saturation. By comparing different
                      models for the voltage coupling coefficient at partial
                      saturation to the experimental data, it was observed that
                      models that relate the voltage coupling coefficient to the
                      relative permeability of the porous medium in addition to
                      the saturation in water were most appropriate. In the case
                      of inversion of TDR data, a comparison of the coupled and
                      uncoupled inversion approaches revealed that the coupled
                      inversion approach is more practical and less uncertain.
                      Particularly it was observed that coupled hydrogeophysical
                      inversion enables simultaneous monitoring of ponding depth
                      and water infiltration, which avoids the laborious task of
                      manually measuring the ponding depths and can thus enable
                      rapid estimation of the soil hydraulic parameters for
                      multiple locations through automatic measurements of ponded
                      infiltration for multiple rings through TDR multiplexing.
                      Future studies should focus on using the coupled
                      hydrogeophysical inversion approach to estimate spatially
                      varying hydraulic properties which are more characteristic
                      of the vadose zone. At the expense of a higher computational
                      cost, better estimates of parameter uncertainties can be
                      obtained with the use of MCMC algorithms that provide
                      posterior probability distributions of the inverted
                      parameters.},
      keywords     = {Dissertation (GND)},
      cin          = {IBG-3},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {246 - Modelling and Monitoring Terrestrial Systems: Methods
                      and Technologies (POF2-246)},
      pid          = {G:(DE-HGF)POF2-246},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/133236},
}