Abstract
Cosmic-Ray neutron sensors are widely used to determine soil moisture on the hectare scale. Precise measurements, especially in the case of mobile application, demand for neutron detectors with high counting rates and high signal-to-noise ratios. For a long time Cosmic Ray Neutron Sensing (CRNS) instruments have relied on $^3$He as an efficient neutron converter. Its ongoing scarcity demands for technological solutions using alternative converters, which are $^6$Li and $^{10}$B. Recent developments lead to a modular neutron detector consisting of several $^{10}$B-lined proportional counter tubes, which feature high counting rates via its large surface area. The modularity allows for individual shieldings of different segments within the detector featuring the capability of gaining spectral information about the detected neutrons. This opens the possibility for active signal correction, especially useful when applied to mobile measurements, where the influence of constantly changing near-field to the overall signal should be corrected. Furthermore, the signal-to-noise ratio could be increased by combining pulse height and pulse length spectra to discriminate between neutrons and other environmental radiation. This novel detector therefore combines high-selective counting electronics with large-scale instrumentation technology.
Highlights
The hydrological cycle and energy transfer at the land-atmosphere interface strongly depend on soil moisture
This study examined critical properties of neutron detectors designed for Cosmic Ray Neutron Sensing and introduced a large-scale detector setup tested in situ at an experimental field site
The typical value of 25 mm accompanied with a thermal neutron shield firstly introduced by Desilets et al (2010) was confirmed to be appropriate for a universal detector approach
Summary
The hydrological cycle and energy transfer at the land-atmosphere interface strongly depend on soil moisture. In recent years Cosmic-Ray Neutron Sensing (CRNS) has become a prominent method for non-invasive soil moisture determination, the basic principles are known for decades (Kodama et al, 1985; Zreda et al, 2008). It measures the environmental hydrogen content within a footprint of several hectares and penetration depths of up to 80 cm (Köhli et al, 2015), which enables CRNS to close the gap between large area and local measurements (Robinson et al, 2008). CRNS relies on the inverse relationship between the above-ground epithermal-to-fast
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