Open-Path System for Rapid Measurements of Water Vapor, Temperature, and GHGs Aboard an UAS

DOE’s Office of Biological and Environmental Research aims to better predict the Earth system to inform domestic policy. In response to this challenge, DOE is researching clouds and their impact on the global climate. To better understand cloud dynamics, researchers need to make very rapid, in situ measurements of water vapor concentration and temperature in the supersaturated regions in clouds. Similar measurements are also needed for greenhouse gases to better understand carbon fluxes. This Small Business Innovative Research program involves the development of compact, lightweight analyzers for very rapid, in-situ monitoring of water vapor concentration and air temperature aboard airborne platforms. The analyzers use tunable diode laser absorption spectroscopy to make real-time, first-principles measurements of both parameters with no memory effects. The resulting systems will be used to study supersaturation and better understand cloud dynamics. These instruments will also be extended to measure greenhouse gases. In Phase I, technical feasibility was demonstrated by developing, testing, and deploying a compact, lightweight prototype instrument for high-speed measurements of water vapor concentration and gas temperature. The prototype, which measured 30 x 17 x 20 cm, weighed 2.2 kg, and used < 10 Watts, provided a precision of better than ±15 ppm and ±0.24 K (1?, 100 Hz) for gas concentration and temperature respectively with excellent linearity. The instrument was deployed for eddy flux and airborne studies. During the latter, the analyzer was mounted to an unmanned aerial vehicle and underwent a series of repeated vertical flights. This flight data showed high-frequency dynamics and indicated the technical feasibility of using the technology to make airborne, high-speed measurements of water vapor and temperature. In Phase II, four fast water flux instruments will be developed, testing, deployed, and delivered. The first instrument will target terrestrial monitoring at an Ameriflux site. The seconds unit will be deployed aboard DOE’s ArcticShark unmanned aerial vehicle for low-lying atmospheric studies. The third analyzer will be designed for DOE’s Bombardier Challenger 850 to allow for higher altitude studies. The final system will be deployed aboard DOE’s tethered balloon systems for slower atmospheric profiling. Finally, the airborne instruments will be delivered to specific Atmospheric Radiation Measurement facilities. The terrestrial unit will be extended to measure greenhouse gases for fast carbon flux studies. In addition to studying climate change, the proposed technology has applicability for measuring trace gases in the semiconductor industry and turbulent flux for the Department of Defense’s high-power laser, directed energy applications.