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@PHDTHESIS{Merz:830197,
      author       = {Merz, Steffen},
      title        = {{D}rying front formation in topmost soillayers as
                      evaporative restraint - {N}on-invasive monitoring by
                      magneticresonance and numerical simulation},
      volume       = {376},
      school       = {Universität Bonn},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek Verlag},
      reportid     = {FZJ-2017-03771},
      isbn         = {978-3-95806-234-4},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {xxii, 108 S.},
      year         = {2017},
      note         = {Universität Bonn, Diss., 2017},
      abstract     = {Evaporation from bare soil surfaces is a highly dynamic
                      process and one major component of the globalwater cycle.
                      Due to the nature of soils as complex porous materials, the
                      process of water loss to the atmospheric boundary layer
                      causes a considerably moisture variation in space and time
                      on larger scales driven by the interplay between internal
                      flow processes and the atmosphere. Particularly the top few
                      centimeters of a soil constitute the source for vaporized
                      water to be dissipated by the atmospheric boundary layer.
                      Prediction of soil moisture changes on large scales is of
                      various interests with regard to water resources management
                      (e.g. in agriculture). To be able to describe the processes
                      driven by evaporation on large scales, small scale
                      measurements with high spatial resolution of moisture in the
                      top most soil layerare mandatory. Within this PhD work,
                      different Magnetic Resonance (MR) concepts/apparatus and
                      sequences were applied and assessed to monitor changes in
                      the moisture content of evaporating soils on various scales
                      in high resolution non-invasively while focusing on their
                      field applicability. Particularly focus was spent on the
                      origin of the dry surface layer as it is predicted by
                      theory. Since the concept of single sided MR is of great
                      potential for direct field applications a unilateral single
                      sided sensor and at hree magnet array were employed and the
                      results were compared to measurements performed on
                      stationary MR magnets of different concepts. During the
                      first phase, the moisture development of pure sand exposed
                      to evaporation was studied. A column consisting of medium
                      sand was evaporated and monitored using different echo based
                      and single point imaging methods employed at a 200 MHz
                      stationary MR magnet. The obtained vertical moisture
                      profiles were compared to the results of a 13.4 MHz mobile
                      unilateral single sided MR sensor (NMRMOUSE)and the pros and
                      cons of each concept were evaluated. As a next step, by
                      proving the convenience of the unilateral sensor, a mini
                      lysimeter consisting of a silt loam was exposed to
                      evaporation underdefined irradiative conditions and soil
                      moisture was monitored using the NMR-MOUSE. The results
                      validate the predictions of a coupled heat, water and vapor
                      flow model. Since soils naturally possess paramagnetic
                      impurities and the clay content can vary considerably, MR
                      measurements become challenging in terms of a decreasing
                      signal to noise ratio (SNR) together with significantly
                      accelerated signal decay what gets particularly tricky with
                      progressing desaturation. These a forementioned inherent
                      soil properties justify the need for feasible MR pulse
                      sequences which ideally reduce signal decrease by relaxation
                      acceleration due to internal and external magnetic field
                      gradients and short detection times to reduce signal loss.
                      ...},
      cin          = {IBG-3},
      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)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2017070506},
      url          = {https://juser.fz-juelich.de/record/830197},
}