Measuring turbulent fluxes with the eddy covariance method has become a widely accepted and powerful tool for the determination of long term data sets for the exchange of momentum, sensible and latent heat and trace gases such as CO2 between the atmosphere and the underlying surface. Several flux networks developed continuous measurements above complex terrain, eg. AmeriFlux and EUROFLUX. The main goal of these is the determination of the net exchange of CO2 between the atmosphere and the underlying surface. Under many conditions the basic assumptions for the eddy covariance method, such as stationarity of the covariances and homogeneity of the surface are not fulfilled. There are often other needs that force flux measurements to be performed above non-ideal terrain, as for example the representativeness of an ecosystem for larger areas or the accessibility and infra-structure of a site. To deal with these non-ideal conditions, several research groups developed quality tests to check whether the basic assumptions of the theory are valid. In the framework of the CARBOEUROFLUX project, we combined quality tests described by Foken & Wichura (1996) with the analytical footprint model of Schmid (1997). The aim was to identify suitable wind sectors and meteorological conditions for flux measurements. These tools were applied on half-hourly data of 18 sites participating in this part of the project. Quality tests were applied on the fluxes of momentum, sensible and latent heat, and on the carbon dioxide flux, respectively. The influence of the topography on the vertical wind component was also checked. At many sites the land-use around the flux towers is not homogeneous or the fetch may not be large enough. So the relative contribution of the land-use type intended to be measured was also investigated. Thus we developed a tool that allows comparative investigations of the measured turbulent fluxes at different sites as well as investigations of possible influences of the surrounding land-use patterns.
Quality analysis applied on eddy covariance measurements at complex forest sites using footprint modelling
F Miglietta;M Nardino;
2005
Abstract
Measuring turbulent fluxes with the eddy covariance method has become a widely accepted and powerful tool for the determination of long term data sets for the exchange of momentum, sensible and latent heat and trace gases such as CO2 between the atmosphere and the underlying surface. Several flux networks developed continuous measurements above complex terrain, eg. AmeriFlux and EUROFLUX. The main goal of these is the determination of the net exchange of CO2 between the atmosphere and the underlying surface. Under many conditions the basic assumptions for the eddy covariance method, such as stationarity of the covariances and homogeneity of the surface are not fulfilled. There are often other needs that force flux measurements to be performed above non-ideal terrain, as for example the representativeness of an ecosystem for larger areas or the accessibility and infra-structure of a site. To deal with these non-ideal conditions, several research groups developed quality tests to check whether the basic assumptions of the theory are valid. In the framework of the CARBOEUROFLUX project, we combined quality tests described by Foken & Wichura (1996) with the analytical footprint model of Schmid (1997). The aim was to identify suitable wind sectors and meteorological conditions for flux measurements. These tools were applied on half-hourly data of 18 sites participating in this part of the project. Quality tests were applied on the fluxes of momentum, sensible and latent heat, and on the carbon dioxide flux, respectively. The influence of the topography on the vertical wind component was also checked. At many sites the land-use around the flux towers is not homogeneous or the fetch may not be large enough. So the relative contribution of the land-use type intended to be measured was also investigated. Thus we developed a tool that allows comparative investigations of the measured turbulent fluxes at different sites as well as investigations of possible influences of the surrounding land-use patterns.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
