Global daily 9 km remotely sensed soil moisture (2015–2025) with microwave radiative transfer-guided learning

Feng, S., Li, A., Zhou, R., Butterbach-Bahl, K., Guan, K., Jin, Z., Looms, M. C., Wang, S., Igel, C., Treat, C., Olesen, J. E., & Wang, S. (2026). Global daily 9 km remotely sensed soil moisture (2015–2025) with microwave radiative transfer-guided learning. Scientific Data. https://doi.org/10.1038/s41597-026-06721-6. Abstract Accurate estimation of surface soil moisture (SM) in terrestrial ecosystems is essential for understanding hydroclimate dynamics. The L-band Soil Moisture Active Passive (SMAP) mission has provided 9-km global daily surface SM since April 2015, using a microwave radiative transfer model (RTM)-based algorithm. However, the performance of this algorithm is often limited in regions with dense vegetation cover and complex surface conditions, due to the application of empirical parameters and oversimplified processes. Based on the microwave RTM, a process-guided machine learning (PGML) was developed to estimate global surface SM at SMAP descending overpass time (6 AM, local time). The independent validation results show that PGML SM has strong agreement with global in-situ SM measurements, with R=0.868 and unbiased RMSE=0.054 m3/m3. This dataset contains 11 years (April 2015 - June 2025) global spatio-temporal consistent surface SM with 9-km spatial resolution at a daily scale. The projection of the PGML_SM is EASE-Grid2.0, and the SM unit is m3 / m3. Data Format and Usage Note This dataset is stored in Network Common Data Form (NetCDF) format with one file per day, defined by two dimensions (latitude and longitude) and a variable surface SM.The file name is designed as “PGML_SM_yyyymmdd_Vx.nc”, where “yyyy” stands for year, “mm” stands for month, “dd” stands for day, and ‘Vx’ stands for version ID. For example, “PGML_SM_20170101_V2.nc” contains the global surface SM distribution on the first day of January 2017 at version 2. Naming convention: PGML_SM_yyyymmdd_Vx.ncProjection: 9-km ESAE-Grid 2.0 (EPSG: 6933)Variable: lat_center: latitudelon_center: longitudepgml_sm: surface soil moisture, valid range is from 0 to 1 m3 / m3pgml_sm_std: standard deviation of surface soil moistureqc: quality control flag (8-bit flag) 00000001: Polluted by water, urban or ice/snow. 00000010: Frozen surface (surface temperature<0℃) 00000100: Dense vegetation (vegetation water content>5kg/m2) 00001000: soil moisture exceeds the soil water capacity