Abstract:

Cosmic−ray neutron sensing (CRNS) method is a new technology enabling soil moisture detection at hectometer scales, bridging the gap between traditional point measurements and remote sensing. This study evaluated the applicability of CRNS in a typical oasis farmland ecosystem using in−situ data collected at the Wulanwusu Agro−meteorological Experiment Station of the China Meteorological Administration from May to November 2020, including CRNS measurements, single−point oven−drying gravimetric data, frequency−domain reflectometry (FDR) data and distributed gravimetric data. The study focused on the relationship between the regional soil moisture content obtained by the CRNS using the N₀ parameter method and the soil moisture content measured by the single−point oven−drying gravimetric method, the FDR method and the distributed oven−drying gravimetric method. The results indicated that the soil moisture content measured by CRNS correlates well with that measured by the single−point oven−drying gravimetric method, especially reflecting the moisture variation characteristics of the surface soil layer (0−30cm) in the experimental site, with a maximum correlation coefficient of 0.66. Due to the influence of the FDR sensor installation depth, CRNS exhibited higher sensitivity to precipitation events than the FDR method. The multilayer mean values of soil moisture content measurements by the FDR method and the CRNS method exhibited a significant linear relationship. For the 0−30cm soil moisture layer, the coefficient of determination R² was 0.57, and the root mean square error (RMSE) was 0.018 cm³·cm⁻³. When compared with the distributed oven−drying gravimetric method, the coefficients of determination (R²) for CRNS were 0.61, 0.61, 0.52 and 0.30 for the 0−5cm, 0−10cm, 0−20cm and 0−35cm soil layers, respectively, with corresponding RMSE values of 0.015, 0.010, 0.011 and 0.017cm³·cm⁻³. In oasis farmland ecosystems, compared to the single−point oven−drying gravimetric method, the FDR method and the distributed oven−drying gravimetric method, the CRNS more accurately reflected the spatiotemporal variation of soil moisture at the regional scale and was more sensitive to minor or low−intensity prolonged precipitation events. It also achieves a more accurate measurement of the average surface soil moisture content.

Key words: Cosmic?ray neutron sensing, Soil moisture, Oven?drying gravimetric method, Frequency domain reflection