Retrieving soil moisture using cosmic-ray neutron technology based on COSMIC model in the desert-oasis region

Cosmic-ray neutron technology could estimate average soil moisture on scale of hectometers by monitoring the neutron intensity near the ground, which has been successfully applied in forest, grassland, farmland, and other ecosystems. To verify the reliability of Cosmic-ray Soil Moisture Interaction Code (COSMIC) model for retrieving mesoscale soil moisture in arid regions, we carried out soil moisture observation experiment by using the cosmic-ray neutron rover in the desert-oasis region of the middle reaches of Heihe River. The results showed that the fast neutron intensity in the desert-oasis region were 350-715 counts·(30 s)^-1, and the calibrated high energy neutron intensity (N_cosmic) were (38.5±2.2) counts·(30 s)^-1, which was affected by land surface characteristics. Both COSMIC model (root mean square error=0.019 g·g^-1) and N₀ equation (root mean square error=0.018 g·g^-1) could well assess the mesoscale soil moisture, with the accuracy of soil moisture being higher considering soil lattice water. The average penetration depth was 19 cm in the oasis region and 36 cm in the desert region during the experiment. COSMIC model could be used to retrieve soil moisture by cosmic ray neutron in the desert-oasis regions, which had great potential to realize data assimilation of surface meteorological-hydrological-ecological variables by combining with land surface models.