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Title:
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Uncertainties in eddy covariance flux measurements assessed from CH4 and N2O observations
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Author(s):
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Kroon, P.S.; Hensen, A.; Jonker, H.; Ouwersloot, H.G.; Vermeulen, A.T.; Bosveld, F.C.
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Published by:
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Publication date:
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ECN
Biomass, Coal and Environmental Research
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18-8-2010
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ECN report number:
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Document type:
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ECN-W--10-030
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Article (scientific)
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Number of pages:
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12
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Published in: Agricultural and Forest Meteorology (Elsevier), , 2010, Vol.150, p.806-816.
Abstract:
The uncertainty in eddy covariance (EC) flux measurements is assessed for CH4 and N2O using data measured at a dairy farm site in the Netherlands in 2006 and 2007. An overview is given of the contributing uncertainties and theirmagnitude. The relative and absolute uncertainty of a 30 min EC flux are estimated for CH4 and N2O using N = 2185 EC fluxes. The average absolute uncertainty and its standard deviation are 500 _ 400 ng C m_2 s_1 for CH4 and 100 _ 100 ng N m_2 s_1 for N2O. The corresponding relative uncertainties have 95% confidence interval ranging from 20% to 300% for CH4 and from 30% to 1800% for N2O. The large relative uncertainties correspond to relatively small EC fluxes. The uncertainties are mainly caused by the uncertainty due to one-point sampling which contributes on average more than 90% to the total uncertainty. The other 10% includes the uncertainty in the correction algorithm for the systematic errors. The uncertainty in a daily and monthly averaged EC flux are estimated for several flux magnitude ranges. The daily and monthly average uncertainty are smaller than 25% and 10% for CH4 and smaller than 50% and 10% for N2O, respectively, based on fluxes larger than 100 ng C m_2 s_1 and 15 ng Nm_2 s_1.
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