Diode Laser Hygrometer and Thermometer for Aerial Vehicles

Atmospheric researchers seek improved hygrometry and thermometry measurements in order to improve atmospheric data sets. In particular, better spatial resolution from airborne instruments has been targeted as a goal. For jet instrumentation, measurement speeds of 50 Hz for water vapor and 100 Hz for temperature are desired. In this project, an instrument will be developed to meet the desired measurement speed for both water vapor and temperature. The foundation of the instrument will be the NSF VCSEL hygrometer which has demonstrated the required sensitivity for water vapor and has recently been upgraded to meet the desired water vapor measurement speed. An optical fast temperature measurement will be added to the instrument design by coupling a second laser beam to monitor the oxygen optical absorption. In the Phase I project, a design for an open path multipass cell with two lasers will be developed. The sensitivity and accuracy of the optical thermometry technique will be assessed. Two different variations of this measurement method will be evaluated. The results of the Phase I project will provide the design information needed to construct a Phase II jet instrument. The technology developed in this project will be useful for performing atmospheric water vapor and temperature measurements for a variety of aerial platforms – manned aircraft, unmanned aerial vehicles, and balloons. The multilaser single optical cell approach will be applicable to many sensing applications for multiple gases.