Neutron Probe Data Processing: Calibration and Conversion to Water Content using Nuclear Magnetic Resonance, and Uncertainty Analysis

This data repository houses neutron probe data and processing information for projects at UC Berkeley's Blue Oak Ranch Reserve (BORR) investigating vadose zone moisture dynamics across hillslopes with opposing aspects.

Throughout our field studies, we encountered several challenges with interpreting the neutron probe data. First, there were many dates where the neutron probe did not pass an in-field chi-squared test indicating that the probe was not producing accurate estimates of neutron counts. Second, in several instances, we encountered anomalous increases or decreases in neutron counts across surveys between time periods where there were no precipitation inputs or evapotranspiration, thus, no significant change in moisture content and neutron count was expected. This indicates that the instrument was likely experiencing drift which has been observed in several previous studies (e.g., Hoedlmoser et al. 2012; Vachaud, Royer, and Cooper 1977; Yao et al. 2004; Zhang 2017). To account for these issues, we eliminated survey dates that failed the chi-squared test or produced anomalous count values. We then quantified the amount of instrument drift by averaging measurements across multiple survey periods at depths in the borehole where no change in neutron count was expected to apply a drift correction. Data, scripts, and further explanation for neutron probe data processing is available as part of this Hydroshare resource.

This research was supported by the National Science Foundation CAREER Grant (Award 2046957), Mildred E. Mathias Graduate Student Research Grant by the University of California Natural Reserve System, and the Betty and Gordon Moore Foundation.