Monitoring Soil Water Content and Effective Measurement Depth of Cosmic-Ray Neutron Sensing in the Tibetan Plateau

Accurate monitoring of soil water content (SWC) in the Tibetan Plateau is crucial for understanding ecohydrological processes and improving regional climate projections. Traditional point sensors lack spatial representativeness, while satellite products suffer from coarse resolution and shallow penetration depth. Cosmic-ray neutron sensing (CRNS) has emerged as a promising intermediate-scale method, but its performance in high-altitude heterogeneous landscapes remains insufficiently understood. In this study, CRNS probes were deployed across three representative ecosystems, accompanied by 540 gravimetric samples and frequency-domain reflectometry (FDR) sensors for calibration and validation. Results demonstrate that CRNS effectively captured temporal SWC variations with root mean square error <0.03 cm 3 cm-3 compared to gravimetric measurements. The effective measurement depth, defined by V86, showed a non-linear decrease with increasing SWC, with reductions exceeding 40% as water content rose from 0.10 to 0.35 cm 3 cm-3. Bayesian uncertainty analysis indicated 95% confidence intervals within ±0.04 cm 3 cm-3 , while deviations were primarily linked to spatial heterogeneity, bulk density, and hydrogen pools from biomass and snow. Despite these challenges, CRNS proved capable of bridging the scale gap between point measurements and satellite observations, offering non-invasive and landscape-representative SWC monitoring. The findings provide methodological insights for depth-aware calibration and demonstrate the potential of CRNS to enhance hydrological modeling and satellite product validation in one of Earth's most climate-sensitive highlands.