Joint Eddycovariance Project


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This site is developed by a special interest group in eddycorrelation. The group and its activities were initiated by Henk de Bruin (Wageningen UR). The group is composed of researchers from:

  • the Royal Netherlands Meteorological Institute (KNMI) in De Bilt (Wim Kohsiek, Bart van den Hurk, Cor Jacobs and Fred Bosveld);
  • Wageningen University, department of Meteorology and Air Quality (WUR-METAIR) (Arjan van Dijk until April 2000, Henk de Bruin);
  • Utrecht University, Institute for Marine and Atmospheric Research Utrecht (IMAU) (Arjan van Dijk since May 2000).

The target of the special interest group is the development of

  • Fundamental understanding of the eddycorrelation method. There are large discrepancies between estimates for terms in the energy balance at the surface obtained via eddycorrelation and estimates found via other methods. With a fundamental basis of the eddycorrelation method we will be better able to eliminate possible causes of differences in observations. Furthermore we will be able to estimate the consequences of certain assumptions for the accuracy of estimated energy fluxes.
  • A protocol for practical use of the eddycorrelation method, including corrections for tilt, trends, distortion etcetera. Where possible the protocol will be implemented in a software library. Measurements which have been done and processed according to this protocol will be more versatile in use. Researchers from different groups can compare their results and conclusions, knowing that they have processed their data equally. Consensus about a protocol will facilitate future experiments by providing the conditions and procedures, which have to be taken into account and followed during the measurements.

The Joint Eddycovariance Project is meant to provide the basics of the eddy-correlation method plus an implementation in practice. Researchers are encouraged to send suggestions / comments / software / improvements that will allow us to improve on the present collection and thus succeed in our goal: making and updating a state of the art guideline and software implementation for eddycovariance measurements.


Our insights are collected in a report. The theory of the eddy-covariance method is deployed in chapter 1. Here the surface fluxes of sensible heat, water vapour, momentum and scalar densities are related to measurable quantities at a finite height above the ground. This is done via continuity and budget equations. In chapter 2 these relations are worked out for practical purposes. A step-by-step recipe is provided for datareduction of eddy-covariance measurements. The software implementation of this recipe in package ECPACK is presented in chapter 3. The report is available as a PDF:

The report was mainly prepared by Arjan van Dijk while at Wageningen University (except for the part on the planar fit method and corrections for flow distortion using 3D ellipsoids).

Software: ECpack

The FORTRAN routines, which implement all steps from the report in practice have been collected in a software library ECpack, and are available for download, along with a two sample programs:

  • ec_ncdf, which can be used to process raw eddy-covariance data applying a wide range of corrections (data are assumed to be stored in NetCDF format; csi2ncdf can be used to prepare data stored in other formats)
  • planang, which is used to calculated planar fit angles (the output of which can be used by ec_ncdf)
The source code is made available under the GNU Public Licence. The routines are functionally separated, which means that the IO-routines are neither integrated with the routines that e.g. estimate tilt-angles nor with the routines that apply corrections to a dataset. Researchers who are looking for routines that 'just give them that angle' are welcome to proceed, but we also serve the poor soul who needs an integrated routine doing all the tricks in one go.

The software is free, but in order to keep track of who is using it (to notify you of updates and bug-fixes), with what equipment, and under what type of conditions, we ask you to send us some details, stating:

  • Name
  • Institute
  • Brand and type of equipment (sonic, thermometer, hygrometer, CO2-analyzer, other)
  • What are the typical conditions, surface types where you perform your eddy-covariance measurements
Please send this information to and you will get ASAP the correct URL to get the software. What we have available for users are the entire source-code + executables for Windows. If you have already registered with us, you know the address where to get those.

In case you use our software in any publication, please acknowledge us by citing the the internal report: Van Dijk, A., Moene, A.F., and De Bruin, H.A.R., 2004: The principles of surface flux physics: theory, practice and description of the ECPACK library, Internal Report 2004/1, Meteorology and Air Quality Group, Wageningen University, Wageningen, the Netherlands, 99 pp.


For any information about this project, suggestions, comments, please contact:

Arnold Moene
Meteorology and Air Quality Group
Wageningen University and Research
Droevendaalsesteeg 4
6708 PB Wageningen
NL - 6708 BP Wageningen
The Netherlands
Phone: (+31) 317 482604
Fax: (+31) 317 482811