Humidity profiling of the troposphere from an airborne platform using  GPS signals

High resolution observations over data-sparse oceanic regions are critical if the trend towards higher resolution global numerical weather prediction (NWP) models is to be converted into tangible improvements in weather forecasting success. GPS radio occultation sounding of the atmosphere from airborne platforms has the potential to fill this unique niche in the global meteorological observing system.

GPS radio occultation sensing of the atmosphere involves sub-horizontal line-of-sight measurements made at normal cruising altitudes as transmitting GPS satellites set or rise behind the horizon. A single 8 hour transatlantic flight could provide more than 22 vertical profiles of water vapor. The large number of humidity profiles, the frequent sampling, and the high vertical resolution in the range from the surface to 200 mbar are exactly the type of observations that are sorely needed, for example, as input for forecasting severe European storm systems that develop over the Atlantic Ocean, or for forecasting hurricanes developing over oceans off the coast of the U.S.

We have proposed to equip a Beechcraft Duchess dual engine aircraft owned by Purdue with the high precision GPS navigation system necessary to demonstrate the feasibility of this type of atmospheric remote sensing. The work is carried out in collaboration with Paul Shepson's atmospheric chemistry group.

We have shown through simulations that the technique is feasible and could provide profiles of water vapor from the surface up to 5 km altitude. There are many technological hurdles to overcome to realize this goal, that make this an exciting and challenging research topic.

See also:

Lesne, O., J. Haase, G. Kirchengast, J. Ramsauer, and W. Poetzi, Sensitivity Analysis of GNSS radio occultation for airborne sounding of the troposphere, Phys. and Chem. of the Earth, 2002.

Healy, S.B., J. Haase, and O. Lesne, Abel transform inversion of radio occultation measurements made with a receiver inside the Earth's atmosphere, Ann. Geophys., 2002.

Proposal for an airborne radio occultation system on a Duchess aircraft