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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 2
Hydrol. Earth Syst. Sci., 17, 453–460, 2013
https://doi.org/10.5194/hess-17-453-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 17, 453–460, 2013
https://doi.org/10.5194/hess-17-453-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Feb 2013

Research article | 01 Feb 2013

A universal calibration function for determination of soil moisture with cosmic-ray neutrons

T. E. Franz, M. Zreda, R. Rosolem, and T. P. A. Ferre T. E. Franz et al.
  • Department of Hydrology and Water Resources, University of Arizona, 1133 E James E Rogers Way, Room 122, Tucson, Arizona, 85721, USA

Abstract. A cosmic-ray soil moisture probe is usually calibrated locally using soil samples collected within its support volume. But such calibration may be difficult or impractical, for example when soil contains stones, in presence of bedrock outcrops, in urban environments, or when the probe is used as a rover. Here we use the neutron transport code MCNPx with observed soil chemistries and pore water distribution to derive a universal calibration function that can be used in such environments. Reasonable estimates of pore water content can be made from neutron intensity measurements and by using measurements of the other hydrogen pools (water vapor, soil lattice water, soil organic carbon, and biomass). Comparisons with independent soil moisture measurements at one cosmic-ray probe site and, separately, at 35 sites, show that the universal calibration function explains more than 79% of the total variability within each dataset, permitting accurate isolation of the soil moisture signal from the measured neutron intensity signal. In addition the framework allows for any of the other hydrogen pools to be separated from the neutron intensity measurements, which may be useful for estimating changes in biomass, biomass water, or exchangeable water in complex environments.

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