Soil moisture (SM) is a key variable in controlling the water, carbon, and energy exchange processes of land atmosphereinterface. One of the widely used approaches to retrieve soil moisture is based on satellite remote sensing technology.However, these spatiotemporally continuous soil moisture products retrieved from microwave remote sensing data arenot able to meet the accuracy requirement of flood prediction and irrigation management due to the coarse spatialresolution. As one of the relatively new passive microwave products, The Fengyun-3B Microwave Radiation Imager(FY-3B/MWRI) soil moisture product was retrieved from passive microwave brightness temperature data based on theQp model. However, it has rarely been applied at the catchment and regional scale due to the coarse resolution with 25-km grid. In this study, the Fengyun-3B soil moisture product was downscaled from 25-km to 1-km based on ModerateResolution Imaging Spectroradiometer (MODIS) data. The downscaling approach uses MODIS land surface temperature(LST) and normalized difference vegetation index (NDVI) to construct soil evaporative efficiency (SEE). The 1-km SMwas then estimated based on the difference value of high resolution and average SEE in original FY3B pixel. Thedownscaling method was applied to every Fengyun-3B pixel in the Naqu area on the Tibetan Plateau to retrieve thedownscaled 1-km resolution FY3B soil moisture product. The downscaling results were validated using the in-situ soilmoisture from Soil Moisture/ Temperature Monitoring Network on the central Tibetan Plateau (TP-STMNS) in August2015. The validation results revealed that the downscaling approach showed promising results. We can conclude that thedownscaled FY3B SM product better characterize the spatial and temporal continuity and have higher consistency withvalidation soil moisture data. The approach proposed in this study are applicable to bare surface or sparse vegetationcovered land surface.
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