Soil moisture is a key environmental variable, important to e.g., farmers, meteorologists, and disaster management units. We fuse surface soil moisture (SSM) estimates from spatio-temporally complementary radar sensors through temporal filtering of their joint signal and obtain a kilometre-scale, daily soil water content product named SCATSAR-SWI. With 25 km Metop ASCAT SSM and 1 km Sentinel-1 SSM serving as input, the SCATSAR-SWI is globally applicable and achieves daily full coverage over operated areas. We employ a near-real-time-capable SCATSAR-SWI algorithm on a fused 3 year ASCAT-Sentinel-1-SSM data cube over Italy, obtaining a consistent set of model parameters, unperturbed by coverage discontinuities. An evaluation of a therefrom generated SCATSAR-SWI dataset, involving a 1 km Soil Water Balance Model (SWBM) over Umbria, yields comprehensively high agreement with the reference data (median R = 0.61 vs. in situ; 0.71 vs. model; 0.83 vs. ASCAT SSM). While the Sentinel-1 signal is attenuated to some extent, the ASCAT's signal dynamics are fully transferred to the SCATSAR-SWI and benefit from the Sentinel-1 parametrisation. Using the SM2RAIN approach, the SCATSAR-SWI shows excellent capability to reproduce 5 day-accumulated rainfall over Italy, with R = 0.89 against observed rainfall. The SCATSAR-SWI is currently in preparation towards operational product dissemination in the Copernicus Global Land Service (CGLS).

Sentinel-1 backscatter data -acquired in dual-polarized (VV/VH) Interferometric Wide (IW) swath mode -show an azimuth angle dependency. The orientation of the tangential plane of the surface observed can alter the backscatter differently depending on the azimuth angle of the viewing geometry. In this study, two years of Sentinel-1 backscatter data over Western Europe have been investigated to show that the azimuthal anisotropy of backscatter is mainly caused by the orientation of the topography's slope. The SRTM-3 digital elevation model (DEM) is used to describe the azimuthal anisotropy in the Tyrolean Alps and in addition, an algorithm is presented to take into account the azimuthal dependency by calculating correction parameters for each relative orbit of Sentinel-1. ARTICLE HISTORY