Infrared fluctuation hygrometry in the atmospheric surface layer

✍ Scribed by M. R. Raupach

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: English
• Weight: 872 KB
• Volume: 104
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49710444006

✦ Synopsis

Abstract

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.