Finapp Cosmic Ray Neutron Sensor
CRNS for soil water content and snow water equivalent
Large scale soil and surface biomass moisture measurement is possible using the Finapp Cosmic Ray Neutron Sensing (CRNS) probes, counting the backscattered neutrons generated by the interaction between cosmic ray (fast neutrons) from the sky and water present in the soil and surface biomass (leaf litter and grass).
Hydrogen atoms (H2O) are present in the surface soil and biomass moisture. By measuring incoming cosmic radiation compared to the backscattered radiation, changes in the soil and biomass moisture content can be monitored and calculated.
This CRNS probe is also a valuable tool for monitoring the Snow Water Equivalent (SWE), which represents the amount of water stored in the snow pack in millimeters. Similar to its function in soil moisture monitoring, an increase in SWE leads to a decrease in the intensity of background neutrons. Consequently, a lower count of slow-energy neutrons indicates a higher SWE value in millimeters.
Finapp, using neutron sensing technologies, returns to the foundations of ICT International, which was founded on research that developed the Neutron Probe technology to measure soil moisture content for irrigation scheduling. This knowledge of neutron behaviour in response to changes in soil water (hydrogen) content enable methodologies to be developed which enable small changes in leaf litter and soil moisture water content to be continuously monitored with high accuracy.
The Finapp neutron sensing probe measures in real-time, large scale surface soil moisture and leaf litter moisture content.
The measurement of neutrons to determine soil moisture content is well proven, and CRNS methodology can measure at a much larger scale than a single, local, point measurement of soil moisture with a traditional sensor. The Finapp provides the latest methodology, including Internet of Things (IoT) connectivity.
How the Cosmic Ray Neutron Sensing Finapp probe works
Neutron sensing technologies count slow neutrons that have been thermalised by collision of fast neutrons or cosmic rays with hydrogen in the soil and which have bounced back to the slow neutron detector. The detectors only count returning slow, low energy neutrons. Neutrons are only slowed down by hydrogen atoms as hydrogen is the only element in the soil of similar size and mass. The count of the slow neutrons indicates the number of hydrogen atoms that have been recorded at a particular soil depth. The only source of hydrogen in soil is within water, and so small changes in soil moisture can be monitored continuously as changes in hydrogen content in the soil and thermalised neutron density.
The Finapp counts the neutrons available at a given time, based on the quantity of water present in that area and the availability of cosmic radiation. This involves the measurement of the incoming cosmic rays (which are fast moving neutrons). The Finapp measures a subatomic particle related to the cosmic neutron: the moun.
With the addition of an ICT International MFR-Node, the Finapp can be converted to an IoT device compatible with other sensors to measure key soil, plant, and environment parameters.
About Fast and Slow Neutrons
The Finapp detector contains Lithium-6; when a neutron hits the detector, a pulse of light is generated and energy is released. Within the detector, a photo-multiplier converts the light to an electronic signal for interpretation within the Finapp.
Incoming fast muon particles are measured by the detector, as they are electrically charged. Once these muons have interacted with (hit) the hydrogen molecules in the soil or surface biomass, they become slow or thermal neutrons. The difference between the fast moving (incoming) and the slow moving (returning) neutrons will give the final count of neutrons related to water content in the soil. Any decrease in neutron count is related to the increase in soil and biomass water content.
About Gamma Ray measurements (Finapp-Monitor only)
Measurement of gamma rays is also possible with the Finapp-Monitor. This measurement allows for precipitation to be detected, as well as biomass water (tree and plant).
Finapp Probes
| Probe | Finapp-SM | Finapp-SMPlus |
| Use | Agriculture, Forests and Slow Changing Environments | Landslides, Flooding, Wildfire and Hydrological Hazards |
| Neutrons Count | 900/h | 1600/h |
| Mouns Count | 4000/h | 5000/h |
| Enclosure | Anti-UV polycarbonate IP67 enclosure of 40x30x17cm. Including brackets for anchoring to 48-50mm pole | Anti-UV polycarbonate IP67 enclosure of 50x40x21cm. Including brackets for anchoring to 48-50mm pole |
| Power | Battery (external 12V) or Solar Panel (20W) | Battery (external 12V) or Solar Panel (20W) |
| Range of Operation | -45°C to + 55°C | -45°C to + 55°C |
Internal Datalogger
All versions of the Finapp are equipped with a datalogger that records:
- Atmospheric pressure
- Internal temperature
- External temperature (optional)
- External relative humidity (optional)
- Auto diagnostic system
Measured data is saved locally on an SD card. The stored parameters are:
- Time stamp (UTC)
- Counting of neutrons – according to models
- Counting of muons – according to the models
- Counting of gamma – according to models
- Atmospheric pressure (hPa)
- Internal temperature (°C)
- External temperature (°C) (optional, dependent on modules)
- External humidity (%) (optional, dependent on modules)
- GPS position (optional, dependent on modules)
- Voltage (V)
Output
Soil moisture (gravimetric or volumetric if soil density is known) averaged (1 value) over a circular area of 5 hectares, up to a depth of 30-50cm in standard conditions.
Installation
About 2m above the ground (detector at about 1.8m from the ground)
Data transmission
- Via API and/or access to FINAPP cloud
- Via SDI-12 or RS-232 port
- Compatible with the ICT International MFR-Node using SDI-12.
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