%0 Journal Article
%A Bircher, S.
%A Andreasen, M.
%A Vuollet, J.
%A Vehvilainen, J.
%A Rautiainen, K.
%A Jonard, Francois
%A Weihermüller, Lutz
%A Zakharova, E.
%A Wigneron, J.-P.
%A Kerr, Y. H.
%T Soil moisture sensor calibration for organic soil surface layers
%J Geoscientific instrumentation, methods and data systems
%V 5
%@ 2193-0856
%C Göttingen
%I Copernicus Publ.
%M FZJ-2016-02451
%P 109-125
%D 2016
%X This paper’s objective is to present generic cali-bration functions for organic surface layers derived for thesoil  moisture  sensors  Decagon  ECH2O  5TE  and  Delta-TThetaProbe  ML2x,  using  material  from  northern  regions,mainly  from  the  Finnish  Meteorological  Institute’s  ArcticResearch Center in Sodankylä and the study area of the Dan-ish  Center  for  Hydrology  (HOBE).  For  the  Decagon  5TEsensor  such  a  function  is  currently  not  reported  in  the  lit-erature. Data were compared with measurements from un-derlying  mineral  soils  including  laboratory  and  field  mea-surements. Shrinkage and charring during drying were con-sidered. For both sensors all field and lab data showed con-sistent trends. For mineral layers with low soil organic mat-ter (SOM) content the validity of the manufacturer’s calibra-tions was demonstrated. Deviating sensor outputs in organicand mineral horizons were identified. For the Decagon 5TE,apparent  relative  permittivities  at  a  given  moisture  contentdecreased for increased SOM content, which was attributedto an increase of bound water in organic materials with largespecific surface areas compared to the studied mineral soils.ThetaProbe  measurements  from  organic  horizons  showedstronger nonlinearity in the sensor response and signal satu-ration in the high-level data. The derived calibration fit func-tions between sensor response and volumetric water contenthold for samples spanning a wide range of humus types withdiffering  SOM  characteristics.  This  strengthens  confidencein  their  validity  under  various  conditions,  rendering  them highly suitable for large-scale applications in remote sensingand land surface modeling studies. Agreement between in-dependent Decagon 5TE and ThetaProbe time series from anorganic surface layer at the Sodankylä site was significantlyimproved  when  the  here-proposed  fit  functions  were  used.Decagon  5TE  data  also  well-reflected  precipitation  events.Thus, Decagon 5TE network data from organic surface lay-ers at the Sodankylä and HOBE sites are based on the here-proposed  natural  log  fit.  The  newly  derived  ThetaProbe  fitfunctions  should  be  used  for  hand-held  applications  only,but prove to be of value for the acquisition of instantaneouslarge-scale soil moisture estimates.
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000378207600010
%R 10.5194/gi-5-109-2016
%U https://juser.fz-juelich.de/record/808931