In the heart of Germany, at the Agrosphere Institute of Forschungszentrum Jülich, a team of researchers led by Sonia Akter has been delving into the intricate world of soil moisture monitoring. Their recent study, published in the journal ‘Sensors’ (translated from German as ‘Sensors’), is shedding new light on the accuracy of soil moisture estimates derived from gamma radiation measurements, a method that could have significant implications for the energy sector.
Soil moisture (SM) monitoring is a critical component of agricultural and energy management, influencing everything from crop yields to power plant operations. Traditional methods of measuring soil moisture can be invasive and labor-intensive, making them less than ideal for large-scale or continuous monitoring. Enter gamma radiation (GR) detectors, a promising non-invasive alternative that leverages the inverse relationship between soil moisture and soil-emitted gamma radiation.
Akter and her team have been exploring this method, initially using low-cost counter-tube detectors that provide a bulk GR response across a wide energy range. However, these detectors are not without their challenges. “Several confounding factors, such as soil radon emanation and biomass, can influence the environmental gamma radiation (EGR) signals,” Akter explains. “This can deteriorate the accuracy of soil moisture estimates obtained from EGR.”
To better understand these confounding factors, the team compared the accuracy of SM estimates from EGR with those from reference potassium-40 GR (1460 keV) measurements, which are less influenced by these factors. They installed a Geiger–Mueller counter (G–M), commonly used for EGR monitoring, and a gamma spectrometer side by side in an agricultural field equipped with in situ sensors to measure reference SM and a meteorological station.
Their findings were enlightening. Daily soil moisture could be predicted with a root mean square error (RMSE) of 3.39 vol. % from potassium-40 using the theoretical value of α = 1.11 obtained from the effective ratio of GR mass attenuation coefficients for the water and solid phase. However, the accuracy was lower for the EGRG–M measurements, with an RMSE of 6.90 vol. %.
Wavelet coherence analysis revealed that the EGRG–M measurements were influenced by radon-induced noise in winter, and biomass shielding had a stronger impact on EGRG–M than on potassium-40 GR estimates of SM during summer. “Our study provides a better understanding of the lower prediction accuracy of EGRG–M and suggests that correcting for biomass can improve SM estimation from the bulk EGR data of operational radioactivity monitoring networks,” Akter notes.
So, what does this mean for the future of soil moisture monitoring and the energy sector? The findings suggest that while gamma radiation detectors hold great promise for non-invasive, large-scale soil moisture monitoring, their accuracy can be significantly impacted by confounding factors. By understanding and correcting for these factors, researchers can improve the accuracy of SM estimates, paving the way for more effective agricultural and energy management strategies.
As Akter and her team continue to explore this fascinating field, their work could shape the future of soil moisture monitoring, offering valuable insights for farmers, energy companies, and environmental scientists alike. In the words of Akter, “This is just the beginning. There’s still so much to learn and discover.”