Cosmic rays continuously reach the earth's surface: from their interaction with the water molecules present in the soil, in plants, in the snow, a suspended "fog" of neutrons is formed. The CRNS probes (cosmic ray neutrons sensing) allow to count these neutrons and therefore to determine the water content present in the soil, in the biomass, in the snow.
The CRNS technique has been known for more than 10 years and validated by many scientific publications. But why use cosmic rays to measure soil moisture, BWE and SWE?
Currently available technologies range from invasive, point-scale approaches to satellite remote sensing.
Point-scale approach is generally precise but it is not suitable for covering large areas since the heterogeneity of the soil and the snowpack determine a great variability of the water content even at short distances. A large number of point sensors should be installed, with high installation and maintenance costs, technical problems and interference with agricultural work.
Satellite remote sensing is not suitable for measuring SWE, however it provides soil moisture and BWE observations at a large scale (>km2). Precision is quite low since signal is sensitive only to the very first centimeters of soil or vegetation and the temporal resolution (often weekly) is not suitable for many applications.
CRNS bridge the gap between point measure and satellite with many advantages:
- its large horizontal footprint - tens of hectares - and depth of penetration - 50cm into the soil, more than 10m into the snow
- allows the quantification of soil moisture/ SWE/ BWE averaged over large areas with a single probe
- it is contactless - probe installed 2 meters above the ground / snow - and not invasive. This increases instrument’s life, reduces maintenance costs and facilitates field operations.
- Continuous monitoring, without interruptions due to external factors