Application of a simple model to estimate the footprint of CO₂/H₂O emission from tall forest

Abstract

The interpretation of eddy covariance flux measurements over inhomogeneous surfaces depends largely on the footprint over which the fluxes are captured. Based on the Schuepp's footprint model, the Gaussian distribution was introduced to take into account the lateral dispersion, and a simple analytical model was proposed to determine the footprint of eddy flux measurements. The model was validated at an eddy flux site in a tall forest in Changbai Mountain, northeast China, and it was demonstrated to give more detailed descriptions of spatial representativeness for CO₂/H₂O flux measurements. The proposed model was evaluated against a relatively complicated analytical footprint model, the FSAM model, and the two models showed reasonable consistency. This study pointed out that the usually used 0.01 isopleth of source weight function for outer-limit boundaries of source area integration may cause systematic underestimation of footprint dimensions, and a 0.001 isopleth was suggested for scalar flux footprint analysis.

Keywords:

• CO₂/H₂O fluxes
• Eddy covariance
• Footprint
• Source area

Acknowledgments

This study was supported by the State Key Laboratory of Forest and Soil Ecology (Grant No. LFSE2013–11) and the Frontier Project of Institute of Applied Ecology, Chinese Academy of Sciences. The authors would like to thank the two anonymous reviewers for their valuable comments and suggestions to improve the paper.