Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2017-148
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
27 Mar 2017
Review status
A revision of this discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Improving Calibration and Validation of Cosmic-Ray Neutron Sensors in the Light of Spatial Sensitivity – Theory and Evidence
Martin Schrön1,2, Markus Köhli1,3,4, Lena Scheiffele5, Joost Iwema6, Heye R. Bogena7, Ling Lv8, Eduardo Martini1, Gabriele Baroni2,5, Rafael Rosolem6,9, Jannis Weimar3, Juliane Mai2,10, Matthias Cuntz2,11, Corinna Rebmann2, Sascha E. Oswald5, Peter Dietrich1, Ulrich Schmidt3, and Steffen Zacharias1 1Dep. Monitoring and Exploration Technologies, Helmholtz Centre for Environmental Research - UFZ Leipzig, Germany
2Dep. Computational Hydrosystems, Helmholtz Centre for Environmental Research - UFZ Leipzig, Germany
3Physikalisches Institut, Heidelberg University, Germany
4Physikalisches Institut, University of Bonn, Germany
5Institute of Earth and Environmental Science, University of Potsdam, Germany
6Faculty of Engineering, University of Bristol, England
7Agrosphere Institute (IBG-3), Forschungszentrum Jülich GmbH, Germany
8Department of Plants, Soils and Climate, Utah State University, USA
9Cabot Institute, University of Bristol, England
10Department of Civil and Environmental Engineering, University of Waterloo, Canada
11INRA, Université de Lorraine, UMR1137 Ecology et Ecophysiologie Forestière, Champenoux, France
Abstract. In the last years the method of cosmic-ray neutron sensing (CRNS) has gained popularity among soil hydrologists, physicists, and land-surface modelers. The sensor provides continuous soil moisture data, averaged over several hectares and tens of decimeters 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 neutrons and water dynamics. Recent insights into environmental neutrons accurately described the spatial sensitivity of the sensor and thus allowed 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 approach is extensively tested with two calibration and four time series datasets from a variety of sites and conditions. In all cases, the revised averaging method robustly improved the performance of the CRNS product and even helped to reveal otherwise hidden hydrological processes. The presented approach increases the overall accuracy of CRNS products and will have impact on all their applications in agriculture, hydrology, and modeling.

Citation: Schrön, M., Köhli, M., Scheiffele, L., Iwema, J., Bogena, H. R., Lv, L., Martini, E., Baroni, G., Rosolem, R., Weimar, J., Mai, J., Cuntz, M., Rebmann, C., Oswald, S. E., Dietrich, P., Schmidt, U., and Zacharias, S.: Improving Calibration and Validation of Cosmic-Ray Neutron Sensors in the Light of Spatial Sensitivity – Theory and Evidence, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-148, in review, 2017.
Martin Schrön et al.
Martin Schrön et al.
Martin Schrön et al.

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Short summary
A large-scale average of near-surface water content can be sensed by cosmic-ray neutron detectors. To interpret, calibrate, and validate the integral signal, it is important to account for its sensitivity to heterogeneous patterns like dry or wet spots. We show how point samples contribute to the neutron signal based on their depth and distance from the detector. This approach robustly improves the sensor performance and data consistency, and even reveals otherwise hidden hydrological features.
A large-scale average of near-surface water content can be sensed by cosmic-ray neutron...
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