Optimised Post-Exposure Image Sharpening Code for L3-CCD Detectors

Journal Article · Fri Feb 22 00:00:00 EST 2008 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2896934· OSTI ID:21055406

Harding, Leon K; Butler, Raymond F; Redfern, R Michael; Sheehan, Brendan J; McDonald, James ^[1]

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1. Centre for Astronomy, National University of Ireland-Galway, University Road, Galway (Ireland)

As light from celestial bodies traverses Earth's atmosphere, the wavefronts are distorted by atmospheric turbulence, thereby lowering the angular resolution of ground-based imaging. Rapid time-series imaging enables Post-Exposure Image Sharpening (PEIS) techniques, which employ shift-and-add frame registration to remove the tip-tilt component of the wavefront error--as well as telescope wobble, thus benefiting all observations. Further resolution gains are possible by selecting only frames with the best instantaneous seeing--a technique sometimes calling 'Lucky Imaging'. We implemented these techniques in the 1990s, with the TRIFFID imaging photon-counting camera, and its associated data reduction software. The software was originally written for time-tagged photon-list data formats, recorded by detectors such as the MAMA. This paper describes our deep re-structuring of the software to handle the 2-d FITS images produced by Low Light Level CCD (L3-CCD) cameras, which have sufficient time-series resolution (>30 Hz) for PEIS. As before, our code can perform straight frame co-addition, use composite reference stars, perform PEIS under several different algorithms to determine the tip/tilt shifts, store 'quality' and shift information for each frame, perform frame selection, and generate exposure-maps for photometric correction. In addition, new code modules apply all 'static' calibrations (bias subtraction, dark subtraction and flat-fielding) to the frames immediately prior to the other algorithms. A unique feature of our PEIS/Lucky Imaging code is the use of bidirectional wiener-filtering. Coupled with the far higher sensitivity of the L3-CCD over the previous TRIFFID detectors, much fainter reference stars and much narrower time windows can be used.

• OSTI ID: 21055406
• Journal Information: AIP Conference Proceedings, Vol. 984, Issue 1; Conference: Conference on high time resolution astrophysics: The Universe at sub-second timescales, Edinburgh, Scotland (United Kingdom), 11-13 Sep 2007; Other Information: DOI: 10.1063/1.2896934; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ALGORITHMS
CALIBRATION
CAMERAS
CHARGE-COUPLED DEVICES
COMPUTER CODES
CORRECTIONS
COSMIC PHOTONS
EARTH ATMOSPHERE
ERRORS
GAIN
IMAGE PROCESSING
IMAGES
INFORMATION
MAPS
RESOLUTION
SENSITIVITY
SENSORS
STARS
TELESCOPE COUNTERS
TURBULENCE