Humidity Probe for Contrail-Cirrus Avoidance

Our proposal provides a measurement technology to detect atmospheric conditions that favor the formation and persistence of aircraft-induced cirrus clouds in real time. These clouds account for the major share of aviationrsquo;s climate impact via radiative forcing. We need aircraft equipped with our technology that fly along the busiest flight corridors combined with adaptive flight routing as mitigation strategy. We are developing a new compact laser-spectroscopic instrument to measure the relevant humidity levels. During Phase I we achieved a relative uncertainty of 110 ppb (0.11 ppm) for real-time data recorded at 1 Hz with a short optical pathlength of only 30 cm. With further data averaging the relative uncertainty improved to ~25 ppb (0.025 ppm) for 1-minute averages. We have demonstrated excellent linearity of response of our Phase I benchtop system between 10 ppm and gt;6000 ppm. Based on simulated vertical profile measurements in the laboratory we estimate the accuracy of our Phase I benchtop system to be 1..2 ppm or ~2 %, whichever is greater. This performance makes our technology highly suitable for the proposed contrail avoidance application onboard aircraft. In Phase II we will further refine the instrument design with a strong focus on manufacturability and low cost. Innovations include an optical-fiber based open-path-free optical system with collimation optics and detector integrated into the sample cell, and a fast and efficient look-up based spectroscopic fit. We are actively planning the demonstration of the Phase II prototype instrument during an aircraft deployment.