Flight Measurements of Aero-Optical Distortions from a Flat-Windowed Turret on the Airborne Aero-Optics Laboratory (AAOL)

Abstract

The optical environment of a flat-window hemisphere-on-cylinder turret during flight tests in Notre Dame’s Airborne Aero-Optics Laboratory was evaluated. Aero-optical aberrations around the turret were measured using a high-speed (up to 20 kHz) ShackHartmann wavefront sensor providing the most complete aero-optical mapping to date. The primary data was acquired at Mach 0.5 at an altitude of 15,000 ft, with a subset of the data collected at Mach 0.4 for verification of scaling relationships. During each flight, data were acquired holding the elevation/azimuthal angle of the aperture constant. Additional data sets were acquired allowing the two planes to slew by, providing statistical data over a large range of aperture angles. The flight test data were also compared to wind tunnel measurements using the identical turret. Finally, using the spatial statistics of the flight data, the use of the Large Aperture Approximation (LAA) to estimate the resulting timeaveraged far-field Strehl ratio is revisited.