Image blurring due to turbulent wakes for airborne systems: simulation and modeling

Abstract

We present our findings from a modeling and simulation effort in which we analyzed the imaging performance of a turreted laser beam director/telescope on a transonic aircraft platform. We used real wavefront sensor (WFS) data collected by the Airborne Aero-Optics Laboratory-Transonic (AAOL-T) test platform at Mach 0.8. Using these WFS data, we quantified the imaging point spread function (PSF) for a variety of line-of-sight (LOS) angles. The LOS angle values sweep from forward-looking angles, through the shock wave to backward-looking angles, imaging through the turbulent wake. Our simulation results show Strehl ratios from 4% to 50% with substantial scattering of energy out to many times larger than the diffraction-limited core. For each LOS angle, we analyzed the imaging modulation transfer function (MTF) which showed a rapid reduction of contrast for low-to-mid range spatial frequencies. We reaffirm that practical limits to usable spatial frequencies require higher imaging signal to noise ratio in the presence of aero-optical disturbances at high Mach number. The presented MTF analysis speaks to the degradation of image-contrast-based tracking algorithms that rely on an illuminator laser propagating through aero-optical aberrations. In conclusion, we discuss the AAOL-T imaging flight test campaigns and the anticipated imaging performance of AAOL-T turret.