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https://doi.org/10.5194/gi-2017-34
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
07 Jul 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Instrumentation, Methods and Data Systems (GI).
Intercomparison of Cosmic-Ray Neutron Sensors andWater Balance Monitoring in an Urban Environment
Martin Schrön1, Steffen Zacharias1, Gary Womack2, Markus Köhli1,3,4, Darin Desilets2, Sascha E. Oswald5, Jan Bumberger1, Hannes Mollenhauer1, Simon Kögler1, Paul Remmler1, Mandy Kasner1,6, Astrid Denk1,7, and Peter Dietrich1 1Dep. Monitoring and Exploration Technologies, Helmholtz Centre for Environmental Research – UFZ Leipzig, Germany
2Hydroinnova LLC, Albuquerque, US
3Physikalisches Institut, Heidelberg University, Germany
4Physikalisches Institut, University of Bonn, Germany
5Institute of Earth and Environmental Science, University of Potsdam, Germany
6Institute of Geosciences and Geography, University of Halle-Wittenberg, Germany
7Dep. of Geosciences, University of Tübingen, Germany
Abstract. Sensor-to-sensor variability is a source of error common to all geoscientific instruments, which needs to be assessed before comparative and applied research can be performed with multiple sensors. Consistency among sensor systems is especially critical when the signal is an integral value that covers a large volume within complex, urban terrain. Cosmic-Ray Neutron Sensors (CRNS) are a recent technology that is used to monitor large-scale environmental water storages, for which a rigorous comparison study of numerous co-located sensors has never been performed. In this work, nine stationary CRNS probes of type CRS1000 were installed in relative proximity on a grass patch surrounded by complex urban terrain. While the dynamics of the neutron count rates were found to be similar, offsets of a few percent from the absolute average neutron count rates were found. Technical adjustments of the individual detection parameters brought all instruments into good agreement. Furthermore, the arrangement of multiple sensors allowed to find a critical integration time of 6 hours above which all sensors showed consistent dynamics in the data and their RMSE fell below 1 % of gravimetric water content. The residual differences between the nine signals indicated local effects of the complex urban terrain at the scale of several meters. Mobile CRNS measurements and spatial neutron transport simulations in the surrounding area (25 ha) have revealed that CRNS detectors are sensitive to sub-footprint heterogeneity despite their large averaging volume. The paved and sealed areas in the footprint furthermore damp the dynamics of the CRNS soil moisture product. We developed strategies to correct for the sealed-area effect based on theoretical insights about the spatial sensitivity of the sensor. This procedure not only led to reliable soil moisture estimation in drying periods, it further revealed a strong signal of interception and evaporation water that emerged over the sealed ground during and shortly after rain events. The presented arrangement offered a unique opportunity to demonstrate the CRNS performance in complex terrain, and the results indicate great potential for further applications in urban water sciences.

Citation: Schrön, M., Zacharias, S., Womack, G., Köhli, M., Desilets, D., Oswald, S. E., Bumberger, J., Mollenhauer, H., Kögler, S., Remmler, P., Kasner, M., Denk, A., and Dietrich, P.: Intercomparison of Cosmic-Ray Neutron Sensors andWater Balance Monitoring in an Urban Environment, Geosci. Instrum. Method. Data Syst. Discuss., https://doi.org/10.5194/gi-2017-34, in review, 2017.
Martin Schrön et al.
Martin Schrön et al.
Martin Schrön et al.

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Short summary
Water monitoring in cities plays a crucial role in times of growing urbanization. The cosmic-ray neutron method is a unique instrument capable of sensing water storages in complex environments, non-invasively, continuously, autonomuously, and representatively in large areas. This study performs rigorous sensor intercomparison and uncertainty analysis to ensure reliable data quality, reveals spatial neutron patterns, and proposes a method to identify intercepted/evaporated water over paved ground.
Water monitoring in cities plays a crucial role in times of growing urbanization. The cosmic-ray...
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