Abstract:
Soil water content is an important hydrological parameter, which is difficult to measure at
a field scale due to its spatial and temporal heterogeneity. The Cosmic Ray Neutron Sensor (CRNS)
is a novel and innovative approach to estimate area-averaged soil water content at an intermediate
scale, which has been implemented across the globe. The CRNS is moderated by all hydrogen sources
within its measurement footprint. In order to isolate the soil water content signal from the neutron
intensity, the other sources of hydrogen need to be accounted for. The CRNS’s applications are
not only limited to soil water content estimation, as it can potentially be used to monitor biomass.
The Two-Streams clear-felling provided the unique opportunity to monitor the cosmic ray neutron
intensities before, during, and after the clear-felling. The cadmium-difference method was used to
obtain the pure thermal and epithermal neutron intensities from the bare and moderated detectors.
The study concluded that the presence of biomass within the site reduced the epithermal neutron
intensity by 12.43% and the N0 value by 13.8%. The use of the neutron ratio to monitor biomass was
evaluated and changes in the neutron ratio coincided with biomass changes and resulted in a high
correlation (R2 of 0.868) with the normalized difference vegetation index (NDVI) and (R2 of 0.817)
leaf area index (LAI). The use of the CRNS to simultaneously monitor soil water content and biomass
will be beneficial in providing more reliable soil water content estimates, provide biomass estimates
at a field scale, and aid in understanding the dynamics between soil water content and vegetation.
