Airborne Spectroscopic Static Temperature Sensor

The goal of this proposal is to develop a high speed, high accuracy method to measure the static air temperature outside an airplane while in flight. This is in response to SBIR sub-topic S11.05 Suborbital Instruments and Sensor Systems for Earth Science Measurements which seeks a method to measure static air temperature “from aircraft to better than 0.1 °C accuracy”. We will use open path, high resolution infrared absorption spectroscopy. We will project a frequency-swept laser beam outside of the aircraft and reflect it back to its source, monitoring the resulting infrared spectrum. The laser will primarily probe undisturbed air which has not yet been affected by the approach of the aircraft. The static air temperature will be extracted from the infrared spectrum by monitoring the relative intensity of two spectral lines which have dramatically different temperature dependence. We expect to achieve measurement precision of at least 25 mK and measurement accuracy of at least 100 mK. The measurement rate can be as fast as 100 Hz which would provide time resolution of 10 ms and spatial resolution of a few meters while flying under cruise conditions. During the Phase I project we will choose the optimal spectral lines and test the spectroscopic precision and accuracy in laboratory tests designed to simulate flight conditions. We will also develop a preliminary optical design for deployment on research aircraft. Finally, we will investigate the structure of the boundary layer around the aircraft in consultation with Boeing engineers to help us choose the optimal optical beam path for a Boeing 777 airframe. The intended application for this open path thermometer will be NASA research flights investigating the formation of persistent contrails in the upper troposphere.