There exists no reliable, practical means of accurately measuring low absolute humidities, particularly if reasonable response times are also required. This instrumentation problem impacts airborne and balloon measurements of tropospheric and stratospheric physical properties, airborne research on cloud characteristics, and routine monitoring in polar regions. Analysis of atmospheric infrared absorption spectra and recent developments in infrared laser technology has led to the development of a new and innovative laser hygrometer concept. The envisaged laser hygrometer offers an outstanding combination of accuracy, sensitivity, and response speed, coupled with high reliability and repeatability in harsh environments, noncryogenic operation, compact size, low-power consumption, and modest cost. The Phase I research objectives include design and construction of a proof-of-concept laser hygrometer, verification of its principal of operation and response function, plus research on a commercial hygrometer design and work plan. A successful research and development effort will result in an accurate, reliable, noncryogenic hygrometer with sensitivity greater than 0. I ppmv and response speed greater than 10 Hz.
