Assessment of soil moisture estimation using cosmic-ray neutron probe: Towards building Korean cOsmic-ray Soil Moisture Observing System (KOSMOS)

Soil moisture is a key factor controlling the hydrological phenomena at the land surface, i.e., the state and movement of water on the ground. Microwave remote sensing from space greatly contributes to reducing the lack of information on surface soil moisture. However, there are still challenges in the practical use of satellite-based soil moisture products for difficult situations such as dense vegetation, surface roughness, coarse spatial resolution, complex topography, etc. This is particularly true in South Korea, where more than 70% of the country is mountainous. Here, ground reference data from an observation network is essential for rigorous validation and retrieval of soil moisture. The Cosmic-Ray Neutron Probe (CRNP) is a promising approach for building a ground soil moisture observation network in areas with dense forests and mountainous terrain. CRNP requires no invasive sensor installation (i.e., no damage to vegetation and no interruption to soils) and also has intermediate spatial coverage that minimizes the scale mismatch between traditional ground data and satellite remote sensing products. This study assesses the applicability of CRNP for monitoring soil moisture in Korea. Hongcheon CRNP site, one of the prototype sites for the Korean cOsmic-ray Soil Moisture Observing System (KOSMOS), was established in August 2022, and this study used the Hongcheon site’s soil moisture datasets (one from CRNP and the others from multiple frequency-domain sensors) to calibrate CRNP-derived soil moisture and to evaluate satellite-based surface soil moisture product. Through this study, we discuss the potential of CRNP for enhancing the ground soil moisture observation network and the possibility of expanding the CRNP network throughout South Korea.   Acknowledgment: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2021R1A6A3A01087645), the National Research Foundation of Korea (NRF) grant funded by Ministry of Science and ICT (202300209986), and BK21 FOUR Program of Agriculture-forestry Bioresource Convergence Center (ABC), Seoul National University, Seoul, Korea.