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 (186Kb)
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9,959,000 Yen (FY2000; 4,970,000Yen)
Eddy correlation method is used worldwide as a standard technique to measure CO2 exchange between terrestrial ecosystems and the atmosphere in flux network sites such as Ameriflux, EUROFLUX and AsiaFlux. In order to improve the evaluation of carbon budget in forests, we examined practical problems of eddy correlation method in data processing, analysis and corrections. Eddy correlation data collected at 41 m height of Tomakomai flux research site (42°44'N, 141°31'E, 115-140 m ASL, Larch forest) using an open-path infrared gas analyzer were provided for the study, and the following results were found: 1) Accurate zero adjustment of sonic anemometer is required to apply coordinate rotation. 2) Trend removal should be applied after eliminating spiky noises and should not be applied when stepwise changes are found in data set. 3) Correction for high-frequency spectral losses due to sensor line averaging and separation was insignificant at the forest site. 4) Correction for the density effects due to heat and water vapor transfer is essential. The magnitude of the density correction often exceeded 50 % of raw flux even in mid-July when the leaves were fully developed. In order to promote inter-site comparison of CO2 budget between flux network sites using different instruments, a campaign measurement for comparing eddy correlation systems using different sonic anemometers and open-path infrared gas analyzers was conducted at 25 m height of the Tomakomai site in mid-July, 2000. Results showed that specific sonic probes possibly underestimate longitudinal wind component, and that differences (standard errors) in CO2 flux between different eddy correlation systems were about 12 % of the daytime maximum CO2 uptake rate.
Eddy correlation, CO2 flux, Open-path analyzer, Density correction, Larch forest