A Novel Downscaling Approach Based on Multifrequency Microwave Radiometry Toward Finer Scale Global Soil Moisture Mapping

Global surface soil moisture (SSM) mapping at a 9-km intermediate resolution from microwave remote sensing could play a pivotal role in advancing detailed global hydrological investigations. Despite the wide recognition of the soil moisture active passive (SMAP) mission’s 9-km SSM products based on oversampling of the L-band radiometry, concerns persist regarding its ability to capture higher SSM heterogeneity at finer resolutions. For addressing this concern, a novel methodological framework was proposed in this study. This framework advocates the downscaling of the SMAP 36-km dataset through a fusion with high-frequency (Ka-band) passive microwave (PMW) observations. The resultant 9-km all-weather SSM product, derived from this novel approach, is evaluated using ground-based measurements worldwide. The findings reveal a significantly enhanced accuracy compared to the SMAP conventional oversampling-based one, especially in areas exhibiting pronounced local variations in SSM patterns. The study therefore represents a substantial step forward, providing new insights into the design and use of a multifrequency satellite radiometer for global SSM mapping.