A Study on the Data Processing and Quality Assessment of the Eddy Covariance System

The eddy covariance(EC) technique can measure turbulent exchanges between surface and atmosphere directly,and is now used widely in all of the flux stations.Since this method is based on certain assumptions,the obtained surface fluxes are not true values if there are no necessary corrections.Recent development and some focal points of the eddy-covariance method are reviewed,and used in the processing of the data collected in Miyun station,which is one of the flux stations near Beijing.The analysis of EC data at Miyun station shows: Despiking and the sonic temperature and coordinate rotation corrections have a rather little effects on the surface sensible and latent fluxes(about 1%),however,coordinate rotation has large effect on the momentum flux.The air density correction(WPL correction) is important for water vapor and CO2 fluxes,and should be applied.The turbulent spectral checks in the data quality evaluation are satisfactory.Turbulence stationarity and integral characteristics are used in the flux data quality analysis.After rigorously data screening,the final result shows that about 75% flux data is good,and 2% flux data need to be discarded.Footprint analysis shows for all day and daytime periods,over 70% source area of the fluxes is located in the interested area(non mountainous region) with over 90% of the biggest contribution points in the area.