The eddy covariance technique is an atmospheric measurement method used to calculate vertical turbulent fluxes within the atmospheric boundary layer. This is the lowest region of the troposphere and is usually well mixed, particularly during daylight hours, due to convective heating from the sun. It is this motion in the lower troposphere that makes the technique possible. A pair of instruments are used: a gas sensor to measure the concentration of carbon dioxide and water vapour at the sensor and a sonic anemometer which provides wind velocity resolved into 3 components (2 horizontal, 1 vertical). In order to properly measure the turbulent properties of the atmosphere the measurements must be made at a high frequency - 20 Hz for the Chilbolton Observatory system.
The measurements produced by the system (aside from gas concentrations and wind velocity) are friction velocity, vertical gas fluxes and sensible and latent heat flux.
The gas analyser is a Licor-7500 and the sonic anemometer is a Metek USA-1. The system has been deployed at Chilbolton since 2008.
Technical specifications of the eddy covariance instruments