Data Processing and Product Analysis of Eddy Covariance Flux Data for WATER

Eddy covariance(EC) flux data processing and quality control is an important procedure to ensure the data quality of each observation station.A large number of flux data measured by EC system have been accumulated based on the project of Watershed Allied Telemetry Experimental Research(WATER) since late 2007.Pre-processing and quality control were performed using improved EdiRe software developed by Edinburgh University to the original EC data at Yingke oasis station,Arou freeze-thaw observation station and Guantan forest station.The basic processing steps on the Level-1 data product including removal of outliers and spikes,tilt correction,sonic virtual temperature correction,time-lag correction,frequency response correction,and correction for density effects(WPL correction).Level-2 data product is generated with initial quality control steps based on Level-1 data product,including atmosphere state stationarity test,overall turbulence characteristics test and turbulent flux statistical characteristics analysis.In this paper,taking EC data of Yingke oasis station in July,2008 as an example,the improvements of each correction steps during EC flux data processing and the contribution of different correction methods to the calculation of turbulent flux were analyzed in detail.The results show that:after sonic virtual temperature correction,sensible heat flux decreased about 7.7%;after time-lag correction,latent heat flux and carbon dioxide flux increased by 3.9% and 2.7% respectively;after frequency response correction,sensible heat flux,latent heat flux and carbon dioxide flux increased by 2.7%,10.5% and 11.6% respectively;after WPL correction,latent heat flux increased by 1.7%,and carbon dioxide flux decreased by 9.8%.Finally,the Level-1 product and Level-2 product were compared with the Campbell real-time processing results,and an overall data accuracy evaluation on each eddy covariance station for these three stations was obtained.It is concluded that the data quality of the Arou freeze-thaw observation station is the best,and that of the Yingke oasis station is better,and that of the Guantan forest station is poor.