Improving calibration and validation of cosmic-ray neutron sensors in the light of spatial sensitivity

  • In the last few years the method of cosmic-ray neutron sensing (CRNS) has gained popularity among hydrologists, physicists, and land-surface modelers. The sensor provides continuous soil moisture data, averaged over several hectares and tens of decimeters in depth. However, the signal still may contain unidentified features of hydrological processes, and many calibration datasets are often required in order to find reliable relations between neutron intensity and water dynamics. Recent insights into environmental neutrons accurately described the spatial sensitivity of the sensor and thus allowed one to quantify the contribution of individual sample locations to the CRNS signal. Consequently, data points of calibration and validation datasets are suggested to be averaged using a more physically based weighting approach. In this work, a revised sensitivity function is used to calculate weighted averages of point data. The function is different from the simple exponential convention by the extraordinary sensitivity to the first fewIn the last few years the method of cosmic-ray neutron sensing (CRNS) has gained popularity among hydrologists, physicists, and land-surface modelers. The sensor provides continuous soil moisture data, averaged over several hectares and tens of decimeters in depth. However, the signal still may contain unidentified features of hydrological processes, and many calibration datasets are often required in order to find reliable relations between neutron intensity and water dynamics. Recent insights into environmental neutrons accurately described the spatial sensitivity of the sensor and thus allowed one to quantify the contribution of individual sample locations to the CRNS signal. Consequently, data points of calibration and validation datasets are suggested to be averaged using a more physically based weighting approach. In this work, a revised sensitivity function is used to calculate weighted averages of point data. The function is different from the simple exponential convention by the extraordinary sensitivity to the first few meters around the probe, and by dependencies on air pressure, air humidity, soil moisture, and vegetation. The approach is extensively tested at six distinct monitoring sites: two sites with multiple calibration datasets and four sites with continuous time series datasets. In all cases, the revised averaging method improved the performance of the CRNS products. The revised approach further helped to reveal hidden hydrological processes which otherwise remained unexplained in the data or were lost in the process of overcalibration. The presented weighting approach increases the overall accuracy of CRNS products and will have an impact on all their applications in agriculture, hydrology, and modeling.show moreshow less

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Author details:Martin Schroen, Markus Koehli, Lena Scheiffele, Joost Iwema, Heye R. Bogena, Ling Lv, Edoardo Martini, Gabriele BaroniORCiDGND, Rafael RosolemORCiD, Jannis Weimar, Juliane Mai, Matthias Cuntz, Corinna Rebmann, Sascha Eric OswaldORCiDGND, Peter Dietrich, Ulrich Schmidt, Steffen ZachariasORCiD
DOI:https://doi.org/10.5194/hess-21-5009-2017
ISSN:1027-5606
ISSN:1607-7938
Title of parent work (English):Hydrology and earth system sciences : HESS
Publisher:Copernicus
Place of publishing:Göttingen
Publication type:Article
Language:English
Year of first publication:2017
Publication year:2017
Release date:2020/04/20
Volume:21
Number of pages:22
First page:5009
Last Page:5030
Funding institution:[EP/L504919/1]; Natural Environment Research Council (A MUlti-scale Soil moisture-Evapotranspiration Dynamics study - AMUSED) [NE/M003086/1]; Deutsche Forschungsgemeinschaft (DFG) [CI 26/13-1, FOR 2131]; Integrated Carbon Observation System (ICOS) infrastructure through the Federal programme [213007]; Terrestrial Environmental Observatories (TERENO), Helmholtz Research Centers in Germany
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Geowissenschaften
Peer review:Referiert
Institution name at the time of the publication:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Erd- und Umweltwissenschaften
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