Enhancing soil moisture retrievals from cosmic ray neutron sensor in a peri-urban agricultural landscape

Cosmic ray neutron sensors (CRNS) provide continuous, non-invasive monitoring of soil water content (SWC) at intermediate spatial scale, while their accuracy in heterogeneous landscapes remains less explored. In this study, a CRNS deployed in a peri-urban patchy agricultural landscape was calibrated using five gravimetric campaigns. SWC measured with CRNS was compared with the mean in situ SWC from a network of nine frequency domain (FD) sensors. Weighted mean volumetric SWC closely matched daily in situ measurements at 10 cm depth (mean difference = 1.7 vol% ± 1.5 vol%). Using the gravimetric sampling campaign with mean SWC near field capacity, combined with corrections for air pressure, incoming muons, water vapor and the short-term JUNG correction, resulted in the lowest RMSE for the measurement period, with a value of 3.81 vol%. Correlation between CRNS and in situ SWC was high and significant ( ρ = 0.84, p < 0.001). Monthly differences between the in situ sensor and the calibrated CRNS SWC were generally below 5 vol%, with no significant differences observed during late summer periods. These results demonstrate that locally calibrated CRNS is suitable for drought monitoring at a heterogeneous rainfed landscape, while its use for other objectives, such as precision irrigation, requires further validation.