Flux footprint functions estimate location and relative importance of passive scalar sources influencing flux measurements at a given receptor height. These footprint estimates strongly vary in size, depending on receptor height, atmospheric stability, and surface roughness.

Reliable footprint calculations from, e.g., Lagrangian stochastic models or LES are computationally expensive and cannot readily be computed for long-term observational programs. To facilitate more accessible footprint estimates, Kljun et al. (2004) introduced a scaling procedure for flux footprint functions over stratifications from convective to stable, and receptor heights ranging from near the surface to the middle of the boundary layer. It has been shown that, when applying this scaling procedure, footprint estimates collapse to an ensemble of similar curves.

Furthermore, a simple parameterisation for the scaled footprint estimates has been presented. This parameterisation accounts for the influence of the roughness length on the footprint and allows for a quick but precise algebraic footprint estimation.

This webpage provides a tool to derive online footprint predictions based on the above parameterisation.

Kljun, N., P. Calanca, M.W. Rotach, H.P. Schmid: 2004, 'A Simple Parameterisation for Flux Footprint Predictions', Boundary-Layer Meteorology, 112, 503-523.

This research was supported by the Swiss National Science Foundation (grant 8220-067600), by the European Commission and the Swiss Ministry of Education and Science (grant 97.0136) within the TMR-project TRAPOS, and by the Swiss Commission for Technology and Innovation (KTI) in the framework of EUROTRAC II (grants 3532.1 and 4092.1).