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@ARTICLE{Bircher:279885,
      author       = {Bircher, S. and Andreasen, M. and Vuollet, J. and
                      Vehviläinen, J. and Rautiainen, K. and Jonard, F. and
                      Weihermüller, L. and Zakharova, E. and Wigneron, J.-P. and
                      Kerr, Y. H.},
      title        = {{S}oil moisture sensor calibration for organic soil surface
                      layers},
      journal      = {Geoscientific instrumentation, methods and data systems
                      discussions},
      volume       = {5},
      number       = {2},
      issn         = {2193-0872},
      address      = {Göttingen},
      publisher    = {Copernicus Publ.},
      reportid     = {FZJ-2015-07761},
      pages        = {447 - 493},
      year         = {2015},
      abstract     = {This paper's objective is to present generic calibration
                      functions for organic surface layers derived for the soil
                      moisture sensors Decagon ECH2O 5TE and Delta-T ThetaProbe
                      ML2x, using material from northern regions, mainly from the
                      Finish Meteorological Institute's Arctic Research Center in
                      Sodankylä and the study area of the Danish Center for
                      Hydrology HOBE. For the Decagon 5TE sensor such a function
                      is currently not reported in literature. Data were compared
                      with measurements from underlying mineral soils including
                      laboratory and field measurements. Shrinkage and charring
                      during drying were considered. For both sensors all field
                      and lab data showed consistent trends. For mineral layers
                      with low soil organic matter (SOM) content the validity of
                      the manufacturer's calibrations was demonstrated. Deviating
                      sensor outputs in organic and mineral horizons were
                      identified: for the Decagon 5TE apparent relative
                      permittivities at a given moisture content decreased for
                      increased SOM content, which was attributed to an increase
                      of bound water in organic materials with large surface areas
                      compared to the studied mineral soils. ThetaProbe
                      measurements from organic horizons showed stronger
                      non-linearity in the sensor response and signal saturation
                      in the high level data. The derived calibration fit
                      functions between sensor response and volumetric water
                      content hold for samples spanning a wide range of humus
                      types with differing SOM characteristics. This strengthens
                      confidence in their validity under various conditions,
                      rendering them highly suitable for large-scale applications
                      in remote sensing and land surface modeling studies.
                      Agreement between independent Decagon 5TE and ThetaProbe
                      time series from an organic surface layer at the Sodankylä
                      site was significantly improved when the here proposed fit
                      functions were used. Decagon 5TE data also well-reflected
                      precipitation events. Thus, Decagon 5TE network data from
                      organic surface layers at the Sodankylä and HOBE sites are
                      based on the here proposed natural log fit. The newly
                      derived ThetaProbe fit functions should be used for
                      hand-held applications only, but in that case proof of value
                      for the acquisition of instantaneous large-scale soil
                      moisture estimates.},
      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},
      doi          = {10.5194/gid-5-447-2015},
      url          = {https://juser.fz-juelich.de/record/279885},
}