A scheme for assessment of quality and uncertainty for long-term eddy-covariance measurements

Worldwide networks for routine measurements of the ecosystem exchange of trace gases, water and energy have been established in the last years. The data observed are intended to validate or drive process-based models and to evaluate ecosystem budgets. This purpose requires comparability of the data sets from different sites, compatible and comprehensive quality flagging, and a harmonized uncertainty quantification. Existing strategies to process the eddy-covariance measurements performed in these networks, however, are manifold. They are known to yield varying results and use different schemes to describe the quality of the output. This presentation, hence, reviews existing quality assessment procedures and suggests a newly composed post-processing strategy. This strategy comprises tests on high-frequency raw data, tests on statistics, fluxes and corrections, and a quantification of error estimates. It will be applied in the recently launched TERENO (Terrestrial Environmental Observatories) network of ecosystem observatories around Germany. Five test data sets from TERENO and CarboEurope-IP were processed using the new scheme. These data sets include two different sonic types, open- and closed-path instruments, tall and low vegetation, as well as flat and complex terrain. The scheme turns out to be robust and applicable to all datasets taken with different terrains and measurement set-ups. The results obtained are used to show coherences between the established flagging scheme and the newly added error determination, which represents essential information for both modelers and for budgeting of fluxes.