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| Home > Publications database > Accuracy of soil moisture estimates from gamma radiation: comparison of bulk and energy-resolved measurements |
| Conference Presentation (After Call) | FZJ-2026-00304 |
; ;
2025
Abstract: Utilizing permanently installed gamma radiation (GR) detectors to monitor soil moisture (SM) is an emerging non-invasive technique that relies on the inverse relation between SM and soil-emitted GR. Our previous study demonstrated the successful estimation of SM from environmental gamma radiation (EGR) measurements using a low-cost counter-tube detector. However, this type of detector captures a bulk GR response over a wide energy range, and the resulting EGR signals are affected by confounding factors such as soil radon emanation and biomass. The extent to which these factors affect the accuracy of SM estimation from EGR is not fully understood. This study aimed to assess the accuracy of SM estimates derived from EGR in comparison with those based on reference measurements of the 40K GR gamma line at 1460 keV, which are less susceptible to such interferences. For this purpose, a Geiger–Mueller (G–M) counter, commonly used for EGR monitoring, and a gamma spectrometer were installed in an agricultural field equipped with in situ SM sensors and a meteorological station. Both the G–M based EGR (EGRG–M) and spectrometry-based 40K measurements were related to reference SM using a theoretically derived functional relationship. To better interpret the EGRG–M measurements, we derived bulk GR (EGRS, comparable to EGRG–M) and GR of the radon progeny 214Bi from the spectral GR measurements. Our results show that daily SM can be predicted less accurately from EGRG–M (RMSE = 6.9 vol.%) than from 40K GR (RMSE = 3.4 vol.%) measurements. Wavelet coherence analysis revealed that the EGRG–M measurements were influenced by radon-induced noise in winter. During summer, biomass shielding affected EGRG–M more strongly than 40K GR measurements. In summary, this study advances the understanding of the limitations in SM estimation from bulk EGR measurements and highlights the potential for improving accuracy through corrections for biomass effects in operational radioactivity monitoring networks.
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