Eddy Covariance A Practical Guide to Measurement and Data Analysis
This highly practical handbook is an exhaustive treatment of eddy covariance measurement that will be of keen interest to scientists who are not necessarily specialists in micrometeorology. The chapters cover measuring fluxes using eddy covariance techniq
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Data Acquisition and Flux Calculations Corinna Rebmann, Olaf Kolle, Bernard Heinesch, Ronald Queck, Andreas Ibrom, and Marc Aubinet
In this chapter, the basic theory and the procedures used to obtain turbulent fluxes of energy, mass, and momentum with the eddy covariance technique will be detailed. This includes a description of data acquisition, pretreatment of high-frequency data and flux calculation.
3.1 Data Transfer and Acquisition The data transfer and acquisition mainly depend on the output data types and measuring frequency of the measuring devices. Different methods are distinguished C. Rebmann () Department Computational Hydrosystems, Helmholtz Centre for Environmental Research – UFZ, 04318 Leipzig, Germany O. Kolle Max-Planck Institute for Biogeochemistry, Jena, Germany e-mail: [email protected] B. Heinesch • M. Aubinet Unit of Biosystem Physics, Gembloux Agro-Bio Tech, University of Liege, 5030 Gembloux, Belgium e-mail: [email protected]; [email protected] R. Queck Department of Meteorology, Institute of Hydrology and Meteorology, TU Dresden (TUD), Dresden, Germany e-mail: [email protected] A. Ibrom Risø National Laboratory, Biosystems Department, Technical University of Denmark (DTU), Roskilde, Denmark Risø National Laboratory for Sustainable Energy, Technical University of Denmark (DTU), Frederiksborgvej 399, 4000, Roskilde, Denmark e-mail: [email protected] M. Aubinet et al. (eds.), Eddy Covariance: A Practical Guide to Measurement and Data Analysis, Springer Atmospheric Sciences, DOI 10.1007/978-94-007-2351-1 3, © Springer ScienceCBusiness Media B.V. 2012
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with respect to digital or analog output signals from the sonic anemometer, the analyzer, or any other additional device. The main requirements for instruments and data acquisition systems used for eddy covariance data are their response time to solve fluctuations up to 10 Hz. This means that the sampling frequency has to be high enough to cover the full range of frequencies carrying the turbulent flux, leading usually to a sampling rate of 10–20 Hz. Data acquisition in general should be flexible with respect to sampling frequency and may depend on the devices used (data logger versus personal computer; type of sonic anemometer or gas analyzer). One needs to distinguish between two major groups of data acquisition systems, namely data loggers or computers. Explicit advantages when using data loggers are robustness, compactness, behavior in difficult conditions (low temperature, high humidity), and, above all, low power consumption, which makes such a system the preferred choice for a solar-powered eddy covariance site, especially in remote places where line power is not available. In this case, however, openpath gas analyzers would be preferred compared to closed-path gas analyzers, the latter needing a pump that consumes significantly more energy. If frequent station supervision and data collection are not feasible, an immediate processing of mean data by a logger may be advisable. In
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