The Joint Eddycovariance Project (JEP): Towards a standard for the interpretation of eddy-covariance measurements

The eddy-covariance technique (EC) is broadly considered to be today's reference method for the estimation of surface fluxes. New methods for flux-estimation have to be successful in tests against this method before they are accepted by the micro-meteorological community. Interestingly enough there is no standard recipe for the processing of EC-data. Some of the widely used corrections have been approximated for limited application to Reynolds-averaged data only, whereas with today's technology the use of raw data is common practice and no approximations have to be made. Other corrections are inter-dependent and require an iterative approach and again others are so marginally known that nobody uses them. There is a lot of improvising involved in EC, with the risk of vulnerability to wishful tuning.

We have started a project to collect the state of the art in eddy-covariance technique, with the aim to set a (continuously developing) standard, to which everybody can refer, contribute and take his recourse. This is done via a discussion forum on the Internet and download sections for a report describing the theoretical and practical details plus a software-package implementing the relevant relations in FORTRAN libraries.

In our presentation we will review how, according to the current state of the JEP-project, measured EC-data should be interpreted. The emphasis will be on new insights, which include: an error-estimate for all derived quantities, iteration-considerations, humidity correction on the raw sonic temperature, oxygen correction for hygrometers and planar fit tilt correction in combination with a correction for flow-distortion.