Eddy Covariance Method
The eddy covariance method relies on the combined high-speed measurements of gas concentrations, temperature, and wind speed, followed by data analysis. To date, there is no single uniform step-by-step execution protocol for eddy covariance flux calculations, but much effort is being made by flux measurement networks (e.g., FluxNet, AmeriFlux, ICOS, CarboEurope, Canadian Carbon Program, and iLEAPS) to unify the procedures of flux calculations via the eddy covariance method.
Instrumentation for Eddy CovarianceThe eddy covariance method is a direct means for measuring turbulent fluxes in the atmospheric boundary layer, near the surface. In a typical setup, sensors are mounted on a tower for measuring fluxes above the atmosphere-vegetation interface and for within-vegetation measurements. The basic instruments include a CO2/H2O analyzer (open path and/or closed path), and a sonic anemometer. Because of the fast vertical movement of the wind and small amounts of gas and water vapor carried by the upward and downward winds, eddy covariance measurements require very sophisticated (fast and precise) instrumentation. To compute turbulent fluxes, measured scalar densities (e.g., temperature from a sonic anemometer, water vapor, CO2, and CH4 from gas analyzers) and 3-dimensional wind components (u, v, and w, from a sonic anemometer) are recorded in a data acquisition system. These data are subsequently processed using flux computation software.