Calibration and correction procedures for cosmic-ray neutron soil moisture probes located across Australia

Hawdon, Aaron, McJannet, David, and Wallace, Jim (2014) Calibration and correction procedures for cosmic-ray neutron soil moisture probes located across Australia. Water Resources Research, 50 (6). pp. 5029-5043.

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Abstract

The cosmic-ray probe (CRP) provides continuous estimates of soil moisture over an area of ~30 ha by counting fast neutrons produced from cosmic rays which are predominantly moderated by water molecules in the soil. This paper describes the setup, measurement correction procedures, and field calibration of CRPs at nine locations across Australia with contrasting soil type, climate, and land cover. These probes form the inaugural Australian CRP network, which is known as CosmOz. CRP measurements require neutron count rates to be corrected for effects of atmospheric pressure, water vapor pressure changes, and variations in incoming neutron intensity. We assess the magnitude and importance of these corrections and present standardized approaches for network-wide analysis. In particular, we present a new approach to correct for incoming neutron intensity variations and test its performance against existing procedures used in other studies. Our field calibration results indicate that a generalized calibration function for relating neutron counts to soil moisture is suitable for all soil types, with the possible exception of very sandy soils with low water content. Using multiple calibration data sets, we demonstrate that the generalized calibration function only applies after accounting for persistent sources of hydrogen in the soil profile. Finally, we demonstrate that by following standardized correction procedures and scaling neutron counting rates of all CRPs to a single reference location, differences in calibrations between sites are related to site biomass. This observation provides a means for estimating biomass at a given location or for deriving coefficients for the calibration function in the absence of field calibration data.

Item ID: 38492
Item Type: Article (Research - C1)
ISSN: 1944-7973
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© 2014. American Geophysical Union. All Rights Reserved. The American Geophysical Union (AGU) allows authors to deposit their journal articles in their institutional repository if the version is the final published citable version of record, the AGU copyright statement is clearly visible on the posting, and the posting is made 6 months after official publication by the AGU.

Funders: CSIRO Water for a Healthy Country Flagship, CSIRO division of Land and Water
Date Deposited: 28 Apr 2015 00:14
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050303 Soil Biology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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