Source Region of Turbulent Fluxes from a Surface (Footprint): Concept and Estimation Methods

The source region of a turbulent flux from a surface or the coverage area when measuring from towers is subject to spatial and temporal variability. The need for accurate estimation of the source region of the measured flux or the footprint has significantly increased with the establishment of stations for long-term monitoring of turbulent exchange over forests and other heterogeneous landscapes and the creation of observation networks for determining the intensity of matter and energy exchange between ecosystems and the atmosphere (FLUXNET, AsiaFlux, RuFlux, and others). The footprint plays a crucial role in optimizing the instrument placement, interpreting time series of measured fluxes, analyzing the variability of fluxes in response to changes in the underlying surface, and estimating the quality of the data collected. However, estimating the footprint remains challenging due to the diversity of the studied fluxes and concentrations of substances. This paper provides an overview of available methods for modeling footprints and discusses their advantages and disadvantages. It also identifies current challenges and ways to improve existing approaches.