Richard Holmes, The Boeing Company; V. S. Rao Gudimetla, Air Force Research Laboratory
Keywords: Imaging, Active Illumination, Deep Turbulence
Abstract:
Image formation with coherent active illumination poses special difficulties due to the presence of laser speckle in the image, which is similar to atmospheric speckle and so is difficult to isolate. On the other hand, it can be proven that atmospheric phase and laser speckle can be separated in the pupil plane. Image reconstructions of isolated, actively-illuminated objects are presented using various algorithms that involve either pupil-plane or focal-plane measurements. The most successful algorithms in deep turbulence involve blind iterative deconvolution in the focal plane and branch-cut estimation in the pupil plane. Significant improvements can be found for Rytov variances up to 0.4 and up to 10 atmospheric coherence lengths (r0) across the aperture, in uniform-turbulence scenarios over a 30 km range. These conditions correspond to roughly one isoplanatic patch per diffraction angle (l/D), and roughly 20 or more isoplanatic patches across the object, and require only about eight frames to form a good image. The results are compared using several image metrics with a corresponding idealized adaptive-optics approach using an incoherent beacon.
Date of Conference: September 11-14, 2018
Track: Poster