A global 1 km resolution daily surface longwave radiation product from MODIS satellite data from 2000-2023.

Surface longwave radiation (SLWR) is one of the two components of the surface radiation budget (SRB), which is a driving force of many land surface process models, the water cycle and climate change. To our knowledge, there are currently no publicly accessible long-term high-resolution (1 km) global daily surface longwave radiation products. We developed hybrid methods for estimating the 1 km resolution instantaneous clear-sky surface longwave upwelling radiation (SLUR) and surface longwave downwelling radiation (SLDR) and the cloud base temperature-based (CBT) single-layer cloud model (SLCM) for estimating the instantaneous cloudy-sky SLDR from MODIS data. The Essential thermaL Infrared remoTe sEnsing (ELITE) broadband emissivity (BBE) product and reanalysis surface temperature were employed to calculate the cloudy-sky SLUR. Synchronized with the diurnal information extracted from the ERA5 reanalysis data, we generated a 1 km resolution all-sky daily surface longwave radiation product (including SLUR and SLDR) via temporal integration. The produced daily SLUR and SLDR were validated via ground measurements collected from 369 sites distributed worldwide from nine flux networks. The root mean square error (RMSE) of the daily SLUR is less than 18 W/m, and the RMSE of the daily SLDR is approximately 25 W/m. The accuracy is commensurate with that of CERES-SYN.