Footprint analysis for measurements over a heterogeneous forest

The air flow and vertical distribution of sources/sinks inside a forest can opy have been taken into account in the analysis of the contribution of sou rces/sinks to measured fluxes and concentrations above a forest. The stocha stic estimators for concentrations and fluxes are described and their evalu ation is performed by simulation of an ensemble of fluid parcel trajectorie s. The influence of the forest canopy on the footprint is important for obs ervation levels up to a few times the forest height. The influence of along -wind turbulent diffusion, which analytical atmospheric surface layer (ASL) footprint models do not account for, is significant even at higher levels. The footprint analysis has been performed to deduce the Douglas fir canopy carbon dioxide uptake from eddy covariance flux measurements above a mixed Douglas fir-beech forest during the pre-leaf periods of the beech. The sca tter in the results indicates that such an analysis is limited, presumably due to horizontal inhomogeneties in flow statistics, which were not include d in trajectory simulation. The analysis, however, is useful for the estima tion of the qualitative effect of the forest canopy on the footprint functi on.