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 Zacharias11Dep. 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
Received: 14 Mar 2017 – Accepted for review: 25 Mar 2017 – Discussion started: 27 Mar 2017
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.
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.