Evaluation of a plot-scale methane emission model using eddy covariance observations and footprint modelling

[摘要] Most plot-scale methane emission models – of which many have beendeveloped in the recent past – are validated using data collectedwith the closed-chamber technique. This method, however, suffersfrom a low spatial representativeness and a poor temporalresolution. Also, during a chamber-flux measurement the air withina chamber is separated from the ambient atmosphere, which negatesthe influence of wind on emissions.

Additionally, some methane models are validated by upscaling fluxesbased on the area-weighted averages of modelled fluxes,and by comparing those to the eddy covariance (EC) flux. Thistechnique is rather inaccurate, as the area of upscaling might bedifferent from the EC tower footprint, therefore introducingsignificant mismatch.

In this study, we present an approach to validate plot-scale methanemodels with EC observations using the footprint-weighted averagemethod. Our results show that the fluxes obtained by thefootprint-weighted average method are of the same magnitude as theEC flux. More importantly, the temporal dynamics of the EC flux ona daily timescale are also captured (r² = 0.7). In contrast,using the area-weighted average method yielded a low (r² = 0.14)correlation with the EC measurements. This shows that thefootprint-weighted average method is preferable when validatingmethane emission models with EC fluxes for areas witha heterogeneous and irregular vegetation pattern.

[学科分类] 地球化学与岩石