Soil moisture sensor calibration for organic soil surface layers

• Published in: Geoscientific Instrumentation, Methods and Data Systems
• Main Authors: Bircher, S., Andreasen, M., Vuollet, J., Vehvilainen, J., Rautiainen, K., Jonard, Francois, Weihermüller, Lutz, Zakharova, E., Wigneron, J.-P., Kerr, Y. H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publ. 2016
• Subjects: info:eu-repo/classification/ddc/550; Sodankylä
• Online Access: https://juser.fz-juelich.de/record/808931; https://juser.fz-juelich.de/search?p=id:%22FZJ-2016-02451%22

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 ...