Cosmic Ray Neutron Soil Moisture Estimation Using Physically Based Site-Specific Conversion Functions
AffiliationDepartment of Hydrology and Atmospheric Sciences, University of Arizona
KeywordsCRN soil moisture method
CRN transport modeling
land cover effect
site-specific conversion functions
thermal-to-epithermal neutron ratio
MetadataShow full item record
PublisherBlackwell Publishing Ltd
CitationAndreasen, M., Jensen, K. H., Bogena, H., Desilets, D., Zreda, M., & Looms, M. C. (2020). Cosmic Ray Neutron Soil Moisture Estimation Using Physically Based Site‐Specific Conversion Functions. Water Resources Research, 56(11), e2019WR026588.
JournalWater Resources Research
RightsCopyright © 2020 American Geophysical Union. All Rights Reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractIn order to advance the use of the cosmic ray neutrons (CRNs) to map soil moisture in heterogeneous landscapes, we need to develop a methodology that reliably estimates soil moisture without having to collect 100+ soil samples for each point along the survey route. In this study, such an approach is developed using physically based modeling with the numerical MCNP neutron transport code. The objective is to determine site-specific conversion functions to estimate soil moisture from CRNs for the dominant land covers. Here, we assess this methodology at three field sites with similar mineral soil composition, but different land covers. First, we ensure that the developed models capture the most important differences in neutron transport behavior across sites. For this, we use measured time series and height profiles of thermal and epithermal neutrons. Then, we compare the estimates obtained from the site-specific conversion functions with the standard N0-calibration function. Finally, we compare the CRN soil moisture estimates with independent soil moisture estimates. Overall, the site-specific models are in agreement with the observed trends in neutron intensities. The site-specific soil moisture is similar to the N0-estimated soil moisture, which results in comparable statistical measures. We show that various land covers have a significant impact on the amount and soil moisture sensitivity of epithermal neutrons, while the thermal neutrons are affected to a less degree. Thereby, thermal-to-epithermal neutron ratios can be used to identify the land cover type and thereby the appropriate conversion function for soil moisture estimation for each point along the survey route. ©2020. American Geophysical Union. All Rights Reserved.
Note6 month embargo; first published: 17 October 2020
VersionFinal published version