Measuring Soil Moisture
The system measures fast neutrons that are produced from interactions of cosmic rays with the atmosphere and top few metres of soil. The intensity of these neutrons are moderated largely by water molecules in the soil. The number of neutrons counted over a period of time is inversely proportional to the amount of water in the soil.
To estimate volumetric water content, each system is calibrated against soil samples that are collected from dry and wet moisture regimes using a standard protocol.
Soil moisture from the Weany Creek CosmOz detector is shown in Figure 3. From this figure it can be seen how sharp increases in soil moisture occur immediately following rainfall and how soil moisture slowly declines with time since the last rain.
Applications of cosmic ray soil moisture probes include; site water balance, irrigation scheduling, calibration of satellite soil moisture estimates, soil water balance, weather model improvement (data/model fusion), catchment water balance modelling, flood forecasting and determination of large scale hydraulic properties.