EC-Frame – a quality-control toolbox for the ECPACK eddy-covariance software

The ECPACK Software developed at the Dutch weather service (KNMI) and the universities of Utrecht and Wageningen is one of the well established eddy-covariance softwares used in current research. It follows the approach of Lenschow et al. (1994) to assign an error value to each flux value to characterize its quality, which is the usual way to express the observational error of a measured quantity. Other authors, however, prefer to express the usability of the calculated fluxes by performing certain test and assigning flags (Vickers & Mahrt, 1997) or quality classes (Foken & Wichura, 1996). Since each of these developed his own software, the the different quality-assessment (QA) systems came along with different eddy-covariance calculation schemes.

In the process of developing the quality-control (QC) and QA scheme for the German TERENO project, a wrapper software around a slightly modified version of ECPACK was developed that incorporates the calculation of error flags after Vickers & Mahrt, quality classes after Foken & Wichura, a few other QC tests, original ECPACK errors (van Dyke,1992), errors after Finkelstein & Sims (2001), as well as target area matching by currently one footprint model (Korman & Meixner, 2001).

An optional correction of lags between anemometer and gas analyzer signals was found to remove the reduction of the calculated flux values that had been observed in the past by comparing ECPACK output to TK2/3 and other software. A Comparison of the flagging schemes and errors also demonstrates several redundancies in the established methods, if applied to mid-latitude vegetated sites. Our software, however, enables further investigations of such kind, under completely different conditions. Furthermore it allows to generate consistent data sets across different networks using different QC/QA schemes.