Abstract

Authors

Yasuda, Y., Watanabe, T.

Year

2001

Title

Comparative Measurements of CO₂ Flux over a Forest Using Closed-path and Open-path CO₂ analysers

Journal

Boundary-Layer Meteorology

Volume

100

Page

191-208

DOI

10.1023/A:1019277003979

Keywords

Closed-path analyser, CO₂ flux, Eddy covariance method, Forest, Frequency response, Open-path analyser

URL

http://www.springerlink.com/content/x576w1q27812q6l0/?p=1929427ddfb345fc9836a552e79a7571&pi=0

Abstract

An eddy covariance system using a closed-path CO₂ analyser was constructed for long-term CO₂flux measurements above a forest, and its total frequency response was valuated experimentally. The amplitude and phase responses of the system were examined through a preliminary test, in which a prescribed pattern of CO₂ fluctuation was input to the system. The result showed that the amplitude of the output from the system was attenuated as frequency increased, with a half-power frequency of 0.3 Hz. The phase was delayed by the air sampling through a long tube, but the delay in phase decreased as frequency increased. We then presented a new technique for the correction of flux loss due to the inadequate system response for the eddy covariance measurements of CO₂ flux. Using the present system and the correction technique, diurnal variations in CO₂ flux were measured over a temperate deciduous forest on three days in 1997. The results were compared with the CO₂ fluxes measured with a fast response open-path gas analyser. The CO₂ fluxes from the closed-path system agreed with those from the open-path system after the Webb, Pearman and Leuning correction was made for the latter. In the present test over a forest, the contribution of the frequency-response correction to the CO₂ fluxes was small and its averaged percentage was only 3%in the daytime. However, the percentage would likely increase, if the system were applied to a shorter vegetation site where high frequency components are more important. The comparison confirmed that we can obtain correct measurements of CO₂ flux using the present closed-path system and the correction technique.

Site

KWG

Remarks

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