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@ARTICLE{Mwangi:875333,
      author       = {Mwangi, Samuel and Zeng, Yijian and Montzka, Carsten and
                      Yu, Lianyu and Su, Zhongbo},
      title        = {{A}ssimilation of {C}osmic‐{R}ay {N}eutron {C}ounts for
                      the {E}stimation of {S}oil {I}ce {C}ontent on the {E}astern
                      {T}ibetan {P}lateau},
      journal      = {Journal of geophysical research / D Atmospheres D},
      volume       = {125},
      number       = {3},
      issn         = {2169-8996},
      address      = {Hoboken, NJ},
      publisher    = {Wiley},
      reportid     = {FZJ-2020-01956},
      pages        = {e2019JD031529},
      year         = {2020},
      abstract     = {Accurate observations and simulations of soil moisture
                      phasal forms are crucial in cold region hydrological
                      studies. In the seasonally frozen ground of eastern Tibetan
                      Plateau, water vapor, liquid, and ice coexist in the
                      frost‐susceptible silty‐loam soil during winter.
                      Quantification of soil ice content is thus vital in the
                      investigation and understanding of the region's
                      freezing‐thawing processes. This study focuses on the
                      retrieval of soil ice content utilizing the in situ soil
                      moisture (i.e., liquid phase) and cosmic ray neutron
                      measurements (i.e., total water including liquid and ice),
                      with Observing System Simulation Experiments. To derive the
                      total soil water from neutron counts, different weighting
                      methods (revised, conventional, and uniform) for calibrating
                      the cosmic‐ray neutron probe (CRNP) were intercompared.
                      The comparison showed that the conventional nonlinear method
                      performed the best. Furthermore, to assimilate fast neutrons
                      using the particle filter, the STEMMUS‐FT (Simultaneous
                      Transfer of Energy, Mass and Momentum in Unsaturated Soil)
                      model was used as the physically based process model, and
                      the COSMIC model (Cosmic‐ray Soil Moisture Interaction
                      Code) used as the observation operator (i.e., forward
                      neutron simulator). Other than background inputs from
                      disturbed initializations in the STEMMUS‐FT, model
                      uncertainties were predefined to assimilate fast neutrons.
                      We observed that with enough spread of uncertainties, the
                      updated states could mimic the CRNP observation. In all
                      setups, assimilating CRNP measurements could enhance total
                      soil water analyses, which consequently led to the improved
                      detection of soil ice content and therefore the freezing
                      thawing‐process at the field scale.},
      cin          = {IBG-3},
      ddc          = {550},
      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:000521086600022},
      doi          = {10.1029/2019JD031529},
      url          = {https://juser.fz-juelich.de/record/875333},
}