The cosmic-ray moisture probe measures high energy cosmic-rays slightly above the land’s surface. The method measures low-energy cosmic-ray neutrons above the soil level. Soil water content affects absorption of neutrons above the surface. The higher the soil water content then the lower the number of neutrons above the surface.
Cosmic-ray probes measure soil water content to a depth of approximately 70cm in dry soil yet only 12cm in wet soil. Spatially, the measurement area is approximately 350m radius. Cosmic-ray probes are ideally suited in relatively uniform landscapes such as large scale agriculture.
COSMOS: The Cosmic-Ray Soil Moisture Observatory System: http://cosmos.hwr.arizona.edu/
- Capacitance or frequency domain
- Time domain reflectometry (TDR)
- Time domain transmissometry (TDT)
- Ground penetrating radar (GPR)