LASER-ACOUSTIC HYGROMETER - PROCEDURE AND RESULTS OF FIELD-MEASUREMENTS

Trial field measurements of humidity fluctuations are taken by a laser -acoustic hygrometer consisting of a CO laser, a mechanical modulator, a detector, an audio-frequency amplifier, and a device for processing signals. The proposed method is based on measuring the intensity of s ound that is generated when pulse-modulated laser radiation is absorbe d in the air. The CO laser spectrum (5.0-5.7 mu m) is within the funda mental vapor absorption band (5.2-7 mu m). This allows a medium-powere d CO laser to be employed for measurements of humidity fluctuations. R adiation with a pulse frequency of 16 kHz, which is required for gener ation of sound waves, is generated by chopper of the CW continuous rad iation CO laser. At the point of sound measurement the laser-beam powe r is about 5 W. An acoustic signal carrying the humidity information i s received by a 1.27-cm microphone installed perpendicular to the beam (d = 0.5 cm) at a distance of 3 cm from its axis. The spectra of abso lute humidity fluctuations over the frequency range (2 X 10(-3)-10 Hz) have been calculated from the measurements when relative humidity ran ges between 27% and 47%. Noise characteristics of the laser-acoustic h ygrometer have been studied.