Eddy covariance



The eddy covariance is a statistical method used in meteorology to analyze high-frequency wind and scalar atmospheric data series, and yields values of fluxes of these properties representing quite large areas. For instance, it is used to measure the net ecosystem flux of carbon from vegetated areas, over long periods in a non-invasive way.

Eddy covariance allows the carbon dioxide flux through an ecosystem to be estimated. A sonic anemometer (measuring wind speed) and infrared beam (measuring carbon dioxide in and out) are usually connected to a tower, above vegetation.

In a nutshell, the 3D wind and another variable (usually CO2 concentration, etc) are decomposed into mean and fluctuating components. The covariance is calculated between the fluctuating component of the vertical wind and the fluctuating component of CO2 concentration. The upward flux of CO2 is proportional to the covariance.

The area from which the detected eddies originate can be described probabilistically. Therefore, the area from which the flux of variable is measured is uncertain.

The effect of sensor separation, finite sampling length, sonic path averaging; as well as other instrumental limitations all lead jointly to systematic underestimation of covariance results. In order to correct for these effects spectrum-dependent correction procedures need to be applied.