COSMOS-UK

The COSMOS-UK network is established and operated by the UK Centre for Ecology and Hydrology (UKCEH). It is the first network to systematically measure soil moisture throughout the UK, and represents a range of climate, soils and vegetation. The network consists of ~50 sites, each recording a number of hydrometeorological and soil variables. Each site hosts a cosmic-ray neutron sensor (CRNS); a novel sensor technology which counts fast neutrons in the surrounding atmosphere. In combination with the recorded hydrometeorological data, neutron counts are used to derive Volumetric Water Content (VWC) over a field scale (~0.1 km2) (COSMOS VWC), at daily resolution. Alongside the CRNS, each site hosts several point soil moisture probes recording at 30 minute resolution. More information is available from the COSMOS-UK website: https://cosmos.ceh.ac.uk/ . The full dataset, along with quality flags, is available at: https://doi.org/10.5285/5060cc27-0b5b-471b-86eb-71f96da0c80f . ************************************************************************************************************ IMPORTANT NOTE: The Cosmic-ray neutron sensor (CRNS) is placed just above the ground and counts the naturally occurring neutrons (originating from cosmic rays). The neutrons are scattered by hydrogen atoms, which are present primarily in the soil water. The CRNS neutron count rate (after corrections) reduces with increasing soil moisture content, and can therefore be used, via a calibration curve, to infer the soil Volumetric Water Content (VWC). The CRNS counts neutrons which may have been scattered many times, such that they may have interacted with the ground soil moisture over distances of more than 200 m from the probe, and from tens centimetres of soil depth. This local scattering of neutrons determines the horizontal and vertical footprint of the sensor, or the measurement support volume, and yields the important characteristic of averaging the soil moisture measurement over a large area. Using neutron scattering models, the typical footprint is determined (~12 hectares), although there is some dependence on the VWC, particularly for the soil depth of measurement. For this reason, the CRNS depth of measurement is given as an average for the time series and location, but it should be appreciated that actual sensing depth will be reduced in wet conditions, compared with dry conditions (from around 10 cm to 30 cm depth respectively). ************************************************************************************************************