Decoding the Multi-Signal Soil Response: Integrating Proximal Gamma, Cosmic-Ray Neutrons, and Sentinel-2 for Plot-Scale Soil Moisture Monitoring

Soil is our most vulnerable and vital resource in the accelerating context of climate change; therefore, protecting its health from erosion and degradation is not only an environmental objective, but an essential requirement for global food security. Central to this challenge is the precise management of soil moisture (SM). However, current monitoring faces a significant scale gap; satellite-derived products often provide coarse spatial resolution that fails to capture plot-level variability, while in situ field sensors and gravimetric sampling, although highly precise, are resource-intensive, spatially limited, and poorly representative of broader field conditions. This research addresses this gap through a multi-scale monitoring approach that integrates Cosmic-Ray Neutron Sensing (CRNS) and Proximal Gamma-Ray Spectroscopy (PGRS) with remote sensing data. This combination provides a ground-based calibration layer that is often missing in purely remote-sensing-based approaches. We present two months of stationary monitoring of neutron counts and gamma radiation, combined with Sentinel-2 satellite observations acquired during the same period. The study was conducted on an experimental plot in a Mediterranean environment (Zaragoza, Spain), and incorporates local meteorological precipitation data and SM values from gravimetric calibration. By exploring how these complementary methods can be jointly utilised, we assess their potential to generate products for the calibration and validation of other datasets. The resulting methodological framework provides a transferable basis for SM validation at the agricultural plot scale, leading to more consistent soil moisture products and, ultimately, supporting sustainable water management in precision agriculture.