COSMOS-UK: the UK national soil moisture measurement network – surface observations for EO Cal/Val applications

The COSMOS-UK network delivers high quality continuous near real-time monitoring of soil moisture and meteorological variables across the whole of the UK, at 48 long-term field-monitoring locations, from 2013 ongoing. UKCEH operate the network on behalf of the Natural Environment Research Council (NERC), as part of their National Capability programme, for the benefit of the national academic research community and the private sector. Research grade datasets are publically available for comparison with EO products as a ground based calibration and validation (Cal/Val) network. A range of in situ data are available, focusing on large area (0.1 km2) soil moisture measurements using Cosmic Ray Neutron Sensors (CRNS), as well as point soil moisture measurements at various soil depths; and when applicable the CRNS is used to derive snow water equivalent. Phenology camera imagery is processed to provide greenness products, cropping patterns, and other vegetation and land use changes; upwelling longwave radiation measurements can be related to land surface temperatures in addition to soil temperature profiles from near surface to 50 cm soil depth. Shortwave radiometers give albedo and cloudiness. Sonic anemometers not only provide wind speed and direction, but are also processed to give sensible heat fluxes, and evapotranspiration is estimated as the residual of the land surface energy balance using net radiation and soil heat flux measurements. The suite of data is an invaluable resource in testing EO products, primarily for SAR and other combined EO soil moisture products, and with great potential for further Cal/Val applications.