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

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

Feb 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc..984..235h&link_type=abstract

HIGH TIME RESOLUTION ASTROPHYSICS: The Universe at Sub-Second Timescales. AIP Conference Proceedings, Volume 984, pp. 235-240 (

Computer Science

Databases

Charge-Coupled Devices, Image Detectors, And Ir Detector Arrays, X- And Gamma-Ray Telescopes And Instrumentation, Time Series Analysis, Time Variability, Image Processing, Astronomical Catalogs, Atlases, Sky Surveys, Databases, Retrieval Systems, Archives, Etc.

Scientific paper

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.

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