Autonomous Monitoring of Soil Moisture & Snow Water Equivalent with Stationary and Mobile Cosmic-Ray Neutron Sensors

Cosmic-ray neutron albedo sensing (CRNS) is a modern technology that can be used to continuously measure the average water content in the environment (i.e., in soil, snow, or vegetation). The sensor footprint encompasses an area of 10-15 hectares and extends to 20-50 decimeters deep into the soil. This method might be an alternative to conventional in-situ sensors or to expensive sampling of soil or snow. It also has the potential to bridge the scale gap between point-scale measurements and remote-sensing data in both, the horizontal and the vertical domain.

Currently, more than 200 sensors are operated in the growing networks of national and continental observatories. CRNS stations are continuously monitoring the local water dynamics at various field sites worldwide. They require almost no maintenance over the years due to a solar module, battery and telemetry. Since the method works non-invasively, the soil is left undisturbed. The passive sensing technique measures natural cosmogenic background radiation which interacts with hydrogen in the ground independent of temperature, frost, or wind effects. CRNS can also be used on mobile platforms for on-demand soil moisture mapping at the field- or regional scale. The sensors are rapidly operational on any ground- or airborne vehicle.

In this presentation we will show various examples of stationary CRNS and their performance compared to traditional sensors at various sites in Germany, Europe, and beyond. We will discuss applications for hydrological modeling and new spatial mapping approaches. The data is particularly useful to study hydrological extreme events, droughts, heatwaves, floods, snow melt/accumulation, and it can be applied as a lower boundary condition in atmospheric models, in hydrological models, or agricultural irrigation management.