Soil Moisture Monitoring

An emerging technology is the Cosmic Ray Neutron Sensor (CRNS). These systems measure naturally occurring neutrons from cosmic rays to understand the moisture levels in soil below the surface, which can help to better understand the impact to plant root systems and nutrients. With such information, we can make better irrigation decisions, conserve energy, and provide better predictive ecological models and warnings for events such as drought and flood conditions. The RDT Cosmic Soil Moisture Monitor (Cosmic-SMM), provides accurate measurements of the water content in soil, providing real-time, critical data to decision makers in irrigation, water management, agriculture, and climate monitoring.

COSMIC-SMM Performance Information
  • Standard Device Dimensions 24″ x 9.5″ x 5.4″ for a 2-device Li-Foil MWPC configuration (1″ thick HDPe weather tight enclosure)
  • 700 – 800 neutron counts per hour (cph) per Li-Foil MWPC device (2-device configuration: 1400 – 1600 cph; 3-device configuration: 2100 – 2400 cph)
    • Altitude: 350 m a.s.l.
    • Mean air relative humidity: 70%
    • Mean atmospheric pressure: 977 kPa
  • Solar powered
  • Can include common weather station sensors: temp, pressure, rain gauge
  • Cellular reach back. Compatible with common data loggers
  • Remote download options (coming soon)

RDT is introducing a new and affordable technology for soil moisture monitoring using cosmic-ray background radiation, the Cosmic Soil Moisture Monitor (Cosmic-SMM). With a high neutron-sensitivity and large sensing-area, it is possible to measure soil moisture content without an on-board radiation source, and instead measure the natural neutron background. The cosmic-ray background is made up of a spectrum of neutron energies, ranging from thermal (0.025 eV) to fast neutrons (>1 MeV). Epithermal neutrons, in the middle of this range (~0.025eV – 1MeV), make up the majority of the neutrons (once thermalized) measured by the neutron detector. When a neutron interacts in hydrogen (water), it loses energy, sometimes all of its energy, and therefore a correlation can be made between the number of neutrons measured by the Cosmic-SMM and the volume of water within the soil.

daily precipitation and study compared with He-3 based contents for Soil moisture monitoring
The daily precipitation during the study period and daily mean Cosmic-SMM measured volumetric water content compared with a He-3 based measured volumetric water content.
Soil Moisture Counts Graph
The normalized (N/N0) corrected cosmic-ray neutron counts from the Cosmic-SMM (Li Foil MWPC devices) and a BF-3 based system.