| Improvement of the accuracy of carbon flux measurements by using a combination of numerical modeling and field measurements P.I./Institution: Stathis Michaelides, Tulane University Co-P.I.: Monique Leclerc, University of Georgia
Summarize in two to four sentences what activities will be carried out in the project: We will develop computational tools for the reduction of errors associated with environmental measurements of gaseous fluxes using Computational Fluid Dynamics (CFD) methods. We will model drainage flows that occur over short vegetation and inside a canopy with CFD and will determine the amount of CO2 fluxes "drained out" and not reflected in the measurements We will quantify flux losses associated with these flows and will develop better methods guiding the interpretation of the gaseous flux data. We use the combination of experimental and numerical methods to better interpret NEE data by developing algorithms for the correction of the measured fluxes. Project Abstract: Typical environmental monitoring of CO2 fluxes, either taken up or respired by terrestrial ecosystems, is based on measurements performed by instruments located on fixed platforms. The instruments provide a spatially varying integrated average, according to flow stability and observation level. Data collection and reduction are typically based on the eddy-covariance method. This method, while useful in a myriad of environmental flows, implicitly assumes no net horizontal CO2 fluxes below the canopy level. The present proposal challenges such assumptions and identifies the shortcomings and pitfalls incurred at many sites. It is apparent that drainage flows, certain horizontal flows that occur as a result of inhomogeneous terrain, and their associated CO2 fluxes cannot be accounted for with the current knowledge and measurement methods. The proposed work will improve the interpretation of NEE measurements made in nocturnal conditions at sites characterized by gullies, small microrelief features or small ridges that exist hundreds of meters away from the observation point. We will use a combination of numerical simulations and environmental measurements above the canopy level and close to the ground, in an integrated effort to develop a methodology aimed at improving the interpretation and reduction of environmental monitoring data. We will concentrate our efforts on the improvement of the monitoring accuracy by accounting for the drainage flows resulting from gullies or neighboring ridges. We will also explore the effect other local terrain inhomogeneities have on measured CO2 fluxes using numerical means. The basic hypothesis tested is that the accuracy and interpretation of CO2 flux measurements, especially under nocturnal conditions, will be significantly improved using a combination of numerical flow modeling and field measurements. Summary in "layman's" terms of what will be done and
why: It is known that drainage flows introduce a high error in
measured CO2 fluxes. We will develop computer programs that will enable
us to simulate air motions inside canopies, including drainage flows.
The codes will yield detailed velocity information inside and above vegetation
canopies, as well as CO2 fluxes. We will also identify a site to monitor
eddy-covariance fluxes, using existing methods as well as measurements
close to the ground. Thus, we will perform simultaneously physical measurements
and numerical simulations. From the understanding of the air motion characteristics
around the measurement point given by the simulations, we will develop
a methodology to account for the contribution of drainage flows to the
measured total CO2 flux and computer programs to correct the data monitoring
in a way that accounts for drainage flows and terrain inhomogeneities.
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