Mauder, M; Foken, T: Impact of post-field data processing on eddy covariance flux estimates and energy balance closure, Meteorol. Zeitschrift, 15, 597-609 (2006)
This study evaluates the impact of post-field data processing methods on eddy covariance flux estimates and the resulting energy balance residual. To that end, a dataset from the LITFASS-2003 field campaign was analysed using an experimental software package. Widely discussed issues in data processing, like an adequate flux aver-aging time, coordinate transformations, and alternative approaches for the correction of density effects are ex-amined. The impact of all the single processing steps on the turbulent flux estimates of sensible heat, latent heat and CO2, as well as the impact on the resulting energy balance residual, is demonstrated. Compared to 30 min covariances without any conversions or corrections, the mean energy balance residual can be reduced by 16% if all necessary procedures are applied to the test dataset. Important procedures for the reduction of the experimen-tal energy balance closure problem are the correction for spectral loss and the correction for density effects. Furthermore, the energy balance residual vanishes almost completely if the covariance averaging time is ex-tended from 30 minutes over 24 hours to 5 days. The low-frequency flux contributions are explained through effects, which are caused by the strong heterogeneity of the landscape surrounding the measurement site. The dependence of CO2 flux estimates on the post-field data processing is even stronger. Their mean value can be changed by a factor of 2 through the correction for density effects. The approach after LIU (2005) leads to an increased net assimilation estimate by 26% compared to the classic WPL correction (WEBB et al., 1980).

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