An intercomparison eddy correlation system for the Fluxnet-Canada Research Network

The Fluxnet-Canada Research Network (FCRN) has committed to rigorous quality assessment of the turbulent flux and climate data collected across the network. Protocols establish common procedures for measurements, processing of eddy correlation (EC) data and gap filling. Furthermore EC measurements at the sites will be checked against an inter-comparison EC system supplied by the University of British Columbia's Biomet and Soil Physics Group. The system consists of a GillR3 sonic anemometer and an LI-7500 open-path as well as an LI-COR LI-7000 closed-path infra-red gas analyser (IRGA) through which air is drawn at a flow rate of 15 l/min. The latter has been improved compared to the earlier model LI-6262 IRGA by faster internal data processing and allowing for higher sample flow through the instrument.

The FCRN inter-comparison system was tested during an international inter-comparison campaign in Davis, CA, in March 2004. Spectral analysis of CO₂ mixing ratio measurements by the open- and closed-path IRGAs showed good agreement in frequency response up to 1 Hz and fluxes calculated using data from both instruments agreed to within 1% for CO2 and to within 2% for water vapour. Evaluations of fluxes measured by the intercomparison system at several FCRN flux tower sites will be presented.