Flight testing of laser-optical techniques for future optical air data sensors

Abstract Optical air data sensors, which can serve as alternatives or supplements to traditional air data systems, have been a subject of ongoing research. These remote sensing optical sensors offer the advantage of measuring primary air data parameters in undisturbed airflow. As active sensors, they can self-diagnose, associating each measurement with an uncertainty and accounting for signal loss due to factors such as icing or light blocking, thus avoiding silent false measurements. In this paper, we discuss a recent flight test campaign of optical measurement techniques for potential development into air data sensors for future aircraft. We used laser Doppler anemometry, which relies on aerosol scattering of laser light, to observe the Doppler shift of scattered light from multiple directions. This enables the reconstruction of the full wind vector and the retrieval of true air speed, angle of attack, and angle of sideslip. A second instrument used tunable diode laser absorption spectroscopy, which measures an individual transition of molecular oxygen in the A band, in order to extract the static pressure from the observed collisional broadening. The techniques were implemented as airborne research instruments on the DLR’s Dassault Falcon 20 aircraft and tested in two campaigns in 2022 under different atmospheric conditions and dynamic maneuvers. We present results from these campaigns, focusing on general sensor performance, measurement rates, accuracy, and experimental challenges that need to be addressed for future applications.