Because of their crucial importance to regional water supplies, mountain snowpacks, which gradually release water as temperatures rise during the spring and summer, need to be carefully monitored. Although a number of techniques have been developed to evaluate snowpack depth and water content, these typically obtain data at either small (<1 meter) or basin-wide scales, leaving a gap at intermediate distances.
To help bridge this gap, Schattan et al. evaluated the feasibility of using cosmic ray neutron sensing as a technique for continuously monitoring alpine snowpacks at a field site in the Austrian Alps. This noninvasive technique, which previously has been used to monitor soil moisture, uses a mounted, aboveground sensor to detect high-energy neutrons. These particles are emitted less frequently from materials with greater moisture contents because hydrogen atoms in water have a high capacity to remove them from the system.
From March 2014 through June 2016, the team collected neutron and traditional point measurements of snow depth and snow water content and then compared the results with additional terrestrial laser scanning snow data. Their findings indicate that even in complex alpine terrain, aboveground neutron sensing can reliably detect a snowpack’s average water content across a footprint spanning about 250 meters and that this technique works in snowpacks with up to 600 millimeters of snow water equivalent, about 6 times more than the previously assumed limit.
These promising results indicate that with additional research and confirmation of its applicability at other locations, cosmic ray neutron sensing may become an important tool to enhance snow system measurements and improve runoff forecasting. In addition, because this technique could contribute to distinguishing between summer snowfall and rainfall events, it may also help to detect snowline elevation, an important parameter in determining whether precipitation events will generate flooding. (Water Resources Research, https://doi.org/10.1002/2016WR020234, 2017)
—Terri Cook, Freelance Writer