The ecosystem observation network comprises continuous measurements of trace gas fluxes between various ecosystems and the atmosphere. The observation sites are distributed across forests, cropland, grassland and mires. The key method to determine the turbulent fluxes is the eddy covariance (EC) technique which is applied not only for water vapour and carbon dioxide, but at some sites also for methane and nitrous oxide.
At each site, the EC measurements are complemented by a number of ancillary measurements of phenology, leaf area index, component fluxes such as soil respiration, and the most important meteorological driving variables. These data are used for the interpretation and quality control (including gap filling) of the EC data. It is expected that the standardized ICOS infrastructure at the ecosystem observation sites will also be used as a basis or reference for other research projects.