Compact laser hygrometer for in-situ measurements of water vapor from small unmanned aerial vehicles

The rate of climate change in the Arctic is larger than elsewhere on Earth. The Arctic has unique and complex couplings and feedbacks between the surface and the atmosphere that in turn modify the radiative balance there differently than elsewhere. Current understanding holds that an increase in downwelling long wave radiative flux, driven by increased water vapor and clouds, may be accelerating climate change. There is a need to measure the thermodynamic state (water vapor, temperature and pressure) of the Arctic troposphere. A new compact sensor payload deployed on a small Unmanned Aircraft System is an efficient route to providing the data needed to advance our understanding. The overall objective of the Phase I project is to demonstrate the feasibility of a compact sensor payload to make high precision measurements of water vapor from a small unmanned aircraft. The payload is based on a diode laser optical absorption sensor and sensitive detection technology. The feasibility will be evaluated through signal modeling, engineering design, and laboratory experiments. In the Phase I program, a design will be developed for a flight- worthy, compact sensor with the precision and accuracy required for the target measurements and that will be deployable on a small unmanned aircraft system. Laboratory experiments will demonstrate the required measurement precision, accuracy, and sensitivity. In the Phase II program, a prototype sensor will be fabricated, tested, and field demonstrated. Predictions of global climate change rely on models incorporating precise knowledge of greenhouse gases such as H2O and clouds. Measurements using the high sensitivity instrument for monitoring water vapor that this program will develop can be used to decrease the uncertainties that still remain. Commercial Applications and Other Benefits: The proposed airborne sensor will enable measurements of water vapor on a wider scale and at higher frequencies than are possible now. This is especially important in monitoring climate change in the Arctic. The larger database from more frequent studies will directly benefit the goals of DoE’s Atmospheric Radiation Monitoring program’s effort to create climate monitoring facilities on the North Slope of Alaska in support of the climate science goals of the Climate and Environmental Sciences Division. The basic sensor platform will be adaptable to applications requiring sensitive measurement of trace gases where sensor robustness and size are critical to performance, such as monitoring networks for greenhouse gases.