BEAREX_08 Eddy Covariance Intercomparison.

An intercomparison of nine identical eddy covariance (EC) systems was conducted for 10 days over a winter wheat field in Bushland, Texas prior to the Bushland Evapotranspiration and Agricultural Remote Sensing Experiment (BEAREX_08) intensive field campaign during the 2008 growing season. This intercomparison is considered necessary to quantify inherent uncertainty of flux estimates due to inconsistencies among identical systems Differences in latent (LE), sensible (H) heat fluxes and carbon dioxide (CO₂) flux as well as other turbulence parameters and net radiation (R_n) due to systematic variations among the nine EC systems were quantified. In addition, an intercomparison of net radiometers was also conducted. The effects of atmospheric conditions, especially advection of heat, and strong winds on the consistency of the flux estimates are documented. Statistical methodologies are described that quantify differences in measured fluxes between the systems and where possible are used to reduce systematic bias. An attempt is made to assign a level of uncertainty in each measured flux, namely H, LE, CO₂ and R_n. This is critical to be able to interpret whether differences in surface fluxes measured by EC systems in diverse and similar sites are significant, and for evaluating output from surface energy balance models.