A high-frequency-modulation spectrometer with a lead-salt diode laser operating in the 4 band of CH 4 at 7.8 m was used as a fast chemical sensor to measure ambient methane concentrations of 2 ppmv ͑parts in 10 6 volume-mixing ratio͒ with a time resolution of 10 Hz for micrometeorological flux measurements. To assess the quality of the data on methane emissions from rice paddy fields, we compared eddy-correlation measurements with simultaneously recorded emission data from the state-of-the-art

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... losed-chamber technique and showed that the closed-chamber measurements were 60%-90% higher than were the eddy-correlation measurements during the campaign. This outcome demonstrates that diode-laser spectroscopy is a valuable tool for quality assurance.