Arctic soil moisture extraction based on FY-3E GNSS- R observations

The Arctic soil moisture presents strong connections with the permafrost degradation, and it is also an important water source for the poleward moisture transport during the Arctic cyclones. Previous studies have showed that the space-borne Global Navigation Satellite System-Reflectometry (GNSS-R) observations can monitor the high spatial and temporal resolution soil moisture at low and mid latitudes. However, there are few researches focusing on soil moisture retrieval over the Arctic due to the limited coverage of past GNSS-R missions. The newly-launched FY-3E GNOS-R (GNSS occultation sounder II-reflectometry) sensor can estimate soil moisture information over the Arctic since it covers nearly global land surface. In this paper, the FY-3E GNOS-R observations as well as elevation from different sources, are combined to establish the non-linear relationship with Soil Moisture Active Passive (SMAP) enhanced soil moisture retrievals with the random forest model. The FY-3E derived soil moisture retrievals at a resolution of 36 km agree well with the in-situ observations from 26 ground sites, with a root-mean-square-error of approximately 0.084 m ³ /m ³ . Additionally, trend in FY-3E SM over the Arctic is consistent with that in SMAP SM during June–September 2023. Typically, the monthly variability of soil moisture has good agreement with net precipitation. However, water inflation and elevation can also influence the distribution of soil moisture.