Estimating Daily Root Zone Soil Moisture at 30 Meters Spatial Resolution by Assimilating Fused Surface Soil Moisture to a Modified Hydrological Model

In this study, a methodology combining multi-source data fusion, hydrological model improvement and data assimilation is proposed for estimating daily seamless root zone soil moisture (RZSM) at a spatial resolution of 30 meters. First, we produced more accurate seamless fused surface soil moisture data by triple collocation and least square merging methods. Then, the Richards equation-based soil moisture module was integrated into the SWAT (Soil and Water Assessment Tool) model. The modified model greatly enhanced the simulation of RZSM compared to the original SWAT model. Finally, the fused product was assimilated into the modified SWAT model using the ensemble Kalman filter algorithm to obtain the RZSM at 30 meters spatial resolution. The results showed that the assimilation further improved the soil moisture simulation capability of the model.