Cosmic ray technology to help climate soil study

UK researchers are hoping to improve our understanding of the climate by using cosmic ray technology to study the soil.

A team from Bristol University plan to combine traditional techniques for measuring the amount of moisture in the soil with satellite data and technology that detects the impact of high-energy radiation from space.

This will allow them to build a more detailed picture of how the soil and the atmosphere interact by exchanging moisture, helping to improve the models used to predict climate and weather.

The project relies on technology developed over the last decade, primarily at the University of Arizona in the US, that measures the amount of hydrogen – and therefore water – in the soil without needing to probe into the ground.

soil sensor
Rafael Rosolem with the cosmic-ray soil moisture sensor installed at the the Federal University of Santa Maria SulFlux site in Brazil.

Cosmic rays are a mysterious form of radiation that originates in space and collides with the Earth’s atmosphere, producing a shower of secondary particles – high-energy neutrons.

When these neutrons reach the Earth’s surface, they are absorbed by hydrogen atoms in the soil and re-emitted with a lower amount of energy, rapidly diffusing through the soil and emerging up to hundreds of metres away from their point of origin.

By measuring the lower energy neutrons emitted from the ground it is possible to determine the amount of hydrogen atoms and therefore water in the soil.

‘The key thing is you don’t need to bury the sensor in the ground,’ research leader Dr Rafael Rosolem told The Engineer. ‘It also relies on a natural source of neutrons. In the past you’d use neutron probes that are radioactive and you bury them in the ground, so the scale at which you’re measuring is also limited.’

Because of the way the neutrons are diffused through the soil the cosmic ray device can accurately detect their presence – and so measure soil moisture – from up to 300m away, allowing measurements to be taken on a much greater scale than conventional probes.

Combining these new measurements with small-scale ones from soil probes and kilometre-scale data from satellite imagery should help build a much more detailed picture of the weather and climate-related factors that affect moisture takeup in the soil.

Rosolem previously worked on adapting the sensor – produced by Arizona-based firm HydroInnova – for this application, developing ways to calibrate the device to account for other sources of hydrogen in the soil and the variability of water vapour.