A combination of quality assessment tools for eddy covariance measurements with footprint modelling for the characterisation of complex sites

The adoption of the eddy covariance technique to estimate surface exchange is based on the assumption that certain meteorological conditions are valid. The most important of these are horizontal homogeneity, steady-state, and non-advective conditions. Since such conditions are often violated under complex terrain conditions, e.g. at flux monitoring sites over forests, this study aims to evaluate the influence of surface heterogeneity to permit a correct interpretation of the measurement results. Quality assessment tools for eddy covariance measurements have been combined with footprint modelling. This makes it possible to define the spatial context of the fluxes, and to include land use features of the surrounding terrain in the analysis. The quality of the flux data for different wind sectors and varying meteorological conditions is also determined, so that the most suitable situations for the collection of high-quality data sets can be identified. Additionally, the flux contribution of the different land use types present in the footprint area is calculated. The results are presented as two-dimensional graphs, which show the spatial distribution of the quality of different fluxes. These graphs identify terrain influences affecting the flux data quality. The evaluation is especially useful for checking to what extent the measured fluxes at a site are representative of a specific type of land use.