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@ARTICLE{Rosenbaum:15979,
      author       = {Rosenbaum, U. and Huisman, J.A. and Vrba, J. and Vereecken,
                      H. and Bogena, H.R.},
      title        = {{C}orrection of {T}emperature and {E}lectrical
                      {C}onductivity {E}ffects on {D}ielectric {P}ermittivity
                      {M}easurements with {ECH}(2){O} {S}ensors},
      journal      = {Vadose zone journal},
      volume       = {10},
      issn         = {1539-1663},
      address      = {Madison, Wis.},
      publisher    = {SSSA},
      reportid     = {PreJuSER-15979},
      pages        = {582 - 593},
      year         = {2011},
      note         = {We gratefully acknowledge the support of the SFB 32
                      "Pattern in Soil-Vegetation-Atmosphere Systems: Monitoring,
                      Modelling and Data Assimilation" funded by the Deutsche
                      Forschungsgemeinschaft (DFG) and by TERENO "Terrestrial
                      Environmental Observatories" funded by the Federal Ministry
                      of Education and Research (BMBF). We gratefully thank Prof.
                      R.H. Jansen (Chair of Electromagnetic Theory, RWTH Aachen
                      University) for help with the network analyzer measurements;
                      A. Weuthen and J. Holtkemeier (Forschungszentrum Juelich),
                      A. Kunoth (Institute for Mathematics, University of
                      Paderborn, Germany), Nirca Gerl, and Anne Lange are thanked
                      for their assistance.},
      abstract     = {The measurement accuracy of low-cost electromagnetic soil
                      water content sensors is often deteriorated by temperature
                      and soil bulk electrical conductivity effects. This study
                      aimed to quantify these effects for the ECH2O EC-5 and 5TE
                      sensors and to derive and test correction functions. In a
                      first experiment, the temperature of eight reference liquids
                      with permittivity ranging from 7 to 42 was varied from 5 to
                      40 degrees C. Both sensor types showed an underestimation of
                      permittivity for low temperature (5-25 degrees C) and an
                      overestimation for high temperature (25-40 degrees C). Next,
                      NaCl was added to increase the conductivity of the reference
                      liquids (up to similar to 2.5 dS m(-1) for a permittivity of
                      26-42, up to similar to 1.5 dS m(-1) for a permittivity of
                      22-26). The permittivity measured with both sensors showed a
                      strong and complicated dependence on electrical
                      conductivity, with both under-and overestimation of
                      permittivity. Using these experimental data, we derived
                      empirical correction functions. The performance of the
                      correction functions for the 5TE sensor was evaluated using
                      coarse sand and silty clay loam soil samples. After
                      correcting for temperature effects, the measured
                      permittivity corresponded well with theoretical predictions
                      from a dielectric mixing model for soil with low electrical
                      conductivity. The conductivity correction function also
                      improved the accuracy of the soil moisture measurements, but
                      only within the validity range of this function. Finally,
                      both temperature and electrical conductivity of the silty
                      clay loam were varied and a sequential application of both
                      correction functions also resulted in permittivity
                      measurements that corresponded well with model predictions.},
      keywords     = {J (WoSType)},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {Terrestrische Umwelt},
      pid          = {G:(DE-Juel1)FUEK407},
      shelfmark    = {Environmental Sciences / Soil Science / Water Resources},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000291396000011},
      doi          = {10.2136/vzj2010.0083},
      url          = {https://juser.fz-juelich.de/record/15979},
}