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| Titel |
Eddy-covariance flux errors due to biases in gas concentration measurements: origins, quantification and correction |
| VerfasserIn |
G. Fratini, D. K. McDermitt, D. Papale |
| 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 ; 11, no. 4 ; Nr. 11, no. 4 (2014-02-21), S.1037-1051 |
| Datensatznummer |
250117240
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| Publikation (Nr.) |
 copernicus.org/bg-11-1037-2014.pdf |
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| Zusammenfassung |
| Errors in gas concentration measurements by infrared gas analysers can occur
during eddy-covariance campaigns, associated with actual or apparent
instrumental drifts or biases due to thermal expansion, dirt
contamination, aging of components or errors in field operations. If
occurring on long timescales (hours to days), these errors are normally
ignored during flux computation, under the assumption that errors in mean
gas concentrations do not affect the estimation of turbulent fluctuations
and, hence, of covariances. By analysing instrument theory of operation, and
using numerical simulations and field data, we show that this is not the
case for instruments with curvilinear calibrations; we further show that if
not appropriately accounted for, concentration biases can lead to roughly
proportional systematic flux errors, where the fractional errors in fluxes
are about 30–40% the fractional errors in concentrations. We quantify
these errors and characterize their dependency on main determinants. We then
propose a correction procedure that largely – potentially completely –
eliminates these errors. The correction, to be applied during flux
computation, is based on knowledge of instrument calibration curves and on
field or laboratory calibration data. Finally, we demonstrate the occurrence
of such errors and validate the correction procedure by means of a field
experiment, and accordingly provide recommendations for in situ operations. |
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