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| Titel |
Uncertainty analysis of eddy covariance CO2 flux measurements for different EC tower distances using an extended two-tower approach |
| VerfasserIn |
H. Post, H. J. Hendricks Franssen, A. Graf, M. Schmidt, H. Vereecken |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 4 ; Nr. 12, no. 4 (2015-02-25), S.1205-1221 |
| Datensatznummer |
250117831
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| Publikation (Nr.) |
 copernicus.org/bg-12-1205-2015.pdf |
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| Zusammenfassung |
| The use of eddy covariance (EC) CO2 flux measurements in data assimilation
and other applications requires an estimate of the random uncertainty. In
previous studies, the (classical) two-tower approach has yielded robust
uncertainty estimates, but care must be taken to meet the often competing
requirements of statistical independence (non-overlapping footprints) and
ecosystem homogeneity when choosing an appropriate tower distance. The role
of the tower distance was investigated with help of a roving station
separated between 8 m and 34 km from a permanent EC grassland station.
Random uncertainty was estimated for five separation distances with the
classical two-tower approach and an extended approach which removed
systematic differences of CO2 fluxes measured at two EC towers. This
analysis was made for a data set where (i) only similar weather conditions at
the two sites were included, and (ii) an unfiltered one. The extended
approach, applied to weather-filtered data for separation distances of 95
and 173 m gave uncertainty estimates in best correspondence with an
independent reference method. The introduced correction for systematic flux
differences considerably reduced the overestimation of the two-tower based
uncertainty of net CO2 flux measurements and decreased the sensitivity
of results to tower distance. We therefore conclude that corrections for
systematic flux differences (e.g., caused by different environmental
conditions at both EC towers) can help to apply the two-tower approach to
more site pairs with less ideal conditions. |
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