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Infrared fluctuation hygrometry in the atmospheric surface layer
Author(s) -
Raupach M. R.
Publication year - 1978
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710444006
Subject(s) - hygrometer , calibration , water vapor , humidity , environmental science , infrared , apparent temperature , transmission (telecommunications) , optics , atmospheric sciences , remote sensing , computational physics , materials science , meteorology , physics , geology , telecommunications , quantum mechanics , computer science
This paper describes a single‐beam infrared fluctuation hygrometer, operating in the 2.7 μm water vapour band. By restricting attention to frequencies making up the atmospheric eddy spectrum, a calibration equation for fluctuations is obtained which is independent of moderately stable instrumental gain parameters. A transmission function appropriate to this type of hygrometer is obtained from the random statistical model of band absorption, and shown to imply: (i) a weak but significant dependence of the calibration upon mean humidity; (ii) a very small contribution to transmission fluctuations from temperature fluctuations, which can often be neglected but which may require correction when the Bowen ratio is high. A suitable calibration method is outlined. The results of a field trial over a shallow lake demonstrate the hygrometer's reliability and operational effectiveness for experimental periods of many weeks, and lead to an estimate of 0.88 for the Kolmogorov coefficient for humidity fluctuations.