Analyse des flux turbulents de vapeur d’eau échangés par un couvert forestier mixte
2008
De Ligne, Anne | Aubinet, Marc | Heinesch, Bernard
The present thesis concerns the study of water vapour fluxes exchanged by a forester cover. The purchased objective has been the determination of a correction factor multiplying the measurements, in order to represent for the best the real water vapour fluxes. Harvested on Vielsalm site (Belgium), these fluxes have been measured by the “eddy covariance” method. The transfer functions used up to now have the major disadvantage to under estimate the correction factor of water vapour fluxes. These ones used up to now were initially conceived for the carbon dioxide fluxes. The first inquiring research has therefore been the establishment of an equation of the function transfer specific to the latent heat. The dependence of the parameters of the transfer function has been prominently displayed towards the relative humidity. Moreover, despite the presence of the filter at its mouthpiece, the minimal clogging up of the tube brings phenomenon of sorption-desorption, even more important if the air sampling is humid. The values of the correction factors resulting from the model built upon the new transfer function possess roughly 10 % more than the correction factors calculated by the initial transfer functions. These correction factors are dependant from the air humidity content and wind speed. On the other hand, it seems that the Kaimal equation, allowing building a co-spectrum of reference for the calculation of the correction factor, is not adapted. Effectively, by replacing Kaimal equation by experimental co-spectrum, we notice that the correction factor decreases deeply. The modelling of the co-spectrum of reference requires an extra study to approach for the best the reality.
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