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| Titel |
Technical note: Time lag correction of aquatic eddy covariance data measured in the presence of waves |
| VerfasserIn |
P. Berg, C. E. Reimers, J. H. Rosman, M. Huettel, M. L. Delgard, M. A. Reidenbach, H. T. Özkan-Haller |
| 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. 22 ; Nr. 12, no. 22 (2015-11-26), S.6721-6735 |
| Datensatznummer |
250118177
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| Publikation (Nr.) |
 copernicus.org/bg-12-6721-2015.pdf |
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| Zusammenfassung |
| Extracting benthic oxygen fluxes from eddy covariance time series measured in
the presence of surface gravity waves requires careful consideration of the
temporal alignment of the vertical velocity and the oxygen concentration.
Using a model based on linear wave theory and measured eddy covariance data,
we show that a substantial error in flux can arise if these two variables
are not aligned correctly in time. We refer to this error in flux as the time
lag bias. In one example, produced with the wave model, we found that an
offset of 0.25 s between the oxygen and the velocity data produced a
2-fold overestimation of the flux. In another example, relying on nighttime
data measured over a seagrass meadow, a similar offset reversed the flux from
an uptake of −50 mmol m−2 d−1 to a release of
40 mmol m−2 d−1. The bias is most acute for data measured at
shallow-water sites with short-period waves and low current velocities. At
moderate or higher current velocities (> 5–10 cm s−1), the bias is
usually insignificant. The widely used traditional time shift correction for
data measured in unidirectional flows, where the maximum numerical flux is
sought, should not be applied in the presence of waves because it tends to
maximize the time lag bias or give unrealistic flux estimates. Based on wave
model predictions and measured data, we propose a new time lag correction
that minimizes the time lag bias. The correction requires that the time
series of both vertical velocity and oxygen concentration contain a clear
periodic wave signal. Because wave motions are often evident in eddy
covariance data measured at shallow-water sites, we encourage more work on
identifying new time lag corrections. |
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