Abstract
A system capable of measuring the fluxes of trace gases was developed. It is based on a simpler version of the eddy-accumulation technique (EA), known as the relaxed eddy-accumulation technique (REA). It accumulates air samples associated with updrafts and downdrafts at a constant flow rate in two containers for later analysis of the trace gas mean concentration. The flux integration is based on the durations of updraft and downdraft events, rather than on the vertical wind velocity (W) as is the case for EA and eddy-correlation (EC) techniques. The flux, calculated by the REA technique, is equal to the difference in the mean concentration of the trace gas of interest between the upward and downward moving eddies, multiplied by the standard deviation of the vertical wind velocity and an empirical coefficient. CO2 fluxes measured for 162 half-hour periods over a soybean field by both EC and REA techniques showed excellent agreement (coefficient of determination,R 2=0.92). The slope (0.985) and the intercept (−0.042 mg m−2 s−1) were not significantly different from 1 and 0, respectively, at the 5% level; and the standard error of estimate was 0.074 mg m−2 s−1. It is also shown that the empirical coefficient can be calculated from either latent or sensible heat fluxes. A model describing the effect on this empirical coefficient of not sampling aroundW equal to zero is proposed.
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Centre for Land and Biological Resources Research Contribution No. 92-212.
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Pattey, E., Desjardins, R.L. & Rochette, P. Accuracy of the relaxed eddy-accumulation technique, evaluated using CO2 flux measurements. Boundary-Layer Meteorol 66, 341–355 (1993). https://doi.org/10.1007/BF00712728
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DOI: https://doi.org/10.1007/BF00712728