NEAR-INFRARED DIODE-LASER AIRBORNE HYGROMETER

We describe a new laser-based hygrometer for ambient water vapor monit oring which uses a fiber-optic coupled, near-infrared diode laser in c onjunction with high frequency wavelength modulation spectroscopy. The instrument operates unattended, uses little power, can be extremely c ompact, and exhibits high detection sensitivity. This instrument was f lown on a KC-135 aircraft for a period of six months and measured fros t points at altitudes between 10 000 and 40 000 ft. The water detectio n sensitivity corresponds to a volume mixing ratio of 8 ppm V. Further improvements including the use of newly designed near-infrared lasers are expected to realize frost points below -100-degrees-C.