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Trail in-the-field measurements of humidity fluctuations are taken by a laser-acoustic hygrometer which involves: a CO-laser, a CO-laser, a mechanical modulator of its radiation, a receiver, an audio-frequency amplifier, and a device for processing signals. The proposed method based on measuring the intensity of sound which is generated when pulse-modulated laser radiation is absorbed in the air. The CO-laser spectrum (5.0-5.7 mkm) is within the fundamental vapor absorption band (5.2-7 mkm). This allows a medium-powered CO-laser to be employed for measurements of humidity fluctuations. Radiation with a pulse recurrence frequency of 16 kHz, which is required for generation of sound waves, is generated by an obturator modulation of the CO-laser continuous radiation. At the point of sound measurement the laser-beam power is about 3 W. An acoustic signal carrying the information on humidity is received by a 1/2 inch microphone installed perpendicular to the beam (d equals 0.5 cm) at a distance of 3 cm from its axis. The spectra of absolute humidity fluctuations over the frequency range (2*10-3 - 10)Hz have been calculated from the obtained realizations for atmospheric conditions when relative humidity ranges between 27 and 47%. Noise characteristics of the laser-acoustic hygrometer have been studied.
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