SMCR: A first satellite-derived all-weather daily/1-km Soil Moisture Climatological Record (1980–2023)

Soil moisture (SM) has long been recognized as one of the essential climate variables. However, there are no satellite-derived global SM climatological records spanning over 30 years at fine spatiotemporal resolution. Based on the latest version of the 25 km CCI SM data and 1 km soil data derived from the SoilGrids, a spatially continuous CCI dataset was first obtained using the triple collocation analysis algorithm with the assistance of SM derived from the ERA5, GLEAM, and GLDAS. Subsequently, SM was derived at a fine resolution of 1 km using a downscaling approach considering the sub-grid variability of hydraulic parameters. Finally, the first satellite-derived SM climatological record (1980-2023) at fine spatiotemporal resolution with global seamless coverage was developed. A comprehensive validation against 372 global in-situ observations yielded an averaged unbiased root mean square error of 0.051 m³/m³. Specifically, a Bayesian statics-based credibility analysis of the validated accuracy was first conducted at four networks with dense observation stations. Results indicated an averaged credibility of 83.5% of the accuracy assessment at these networks.