Progress in image formation in deep turbulence with laser illumination

R. Holmes; V. S. Rao Gudimetla

doi:10.1117/12.2501895

18 September 2018 Progress in image formation in deep turbulence with laser illumination

R. Holmes, V. S. Rao Gudimetla

Proceedings Volume 10772, Unconventional and Indirect Imaging, Image Reconstruction, and Wavefront Sensing 2018; 1077204 (2018) https://doi.org/10.1117/12.2501895
Event: SPIE Optical Engineering + Applications, 2018, San Diego, California, United States

Abstract

Formation of images in strong turbulence (spherical-wave log-amplitude variance greater than 0.25) is a well-known challenge. Such imaging 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 it is difficult to separate the two forms of speckle. However, imaging with laser illumination has the potential benefit of enhanced signal and added information in the laser speckle. In this paper, several image processing approaches are investigated with simulation that show promise for good image quality in such conditions. These approaches include pupil-plane techniques that filter phase based on an assumed atmospheric spatial phase structure function, branch-cut filtering and intensity-weighted branch cut minimization. Also included in the analyses are focal-plane techniques. Significant improvements can be found for Rytov variances up to and beyond 0.4 and up to 10 atmospheric coherence lengths (r₀) across the aperture, in uniform turbulence scenarios over a 30 km range with objects of limited extent. The approaches are optimized for fast execution and minimal number of image frames required to form an acceptable image. The results are compared using several image metrics and also compared with a corresponding idealized adaptive-optics approach using an incoherent beacon.

Conference Presentation

Citation Download Citation

R. Holmes and V. S. Rao Gudimetla "Progress in image formation in deep turbulence with laser illumination", Proc. SPIE 10772, Unconventional and Indirect Imaging, Image Reconstruction, and Wavefront Sensing 2018, 1077204 (18 September 2018); https://doi.org/10.1117/12.2501895

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