Re: Orbital surveillance satellites now exceed 1 inch resolution?

From: Allen Thomson (thomsona@flash.net)
Date: Thu May 03 2007 - 16:20:42 EDT

  • Next message: John Locker: "Re: Orbital surveillance satellites now exceed 1 inch resolution?"

    --- Robert Clark <bobbygc2001@yahoo.com> wrote:
    
    > I've just been informed on the Bautforum.com list in a thread under
    this same title that I didn't take into account the effects of
    atmospheric distortion. This limits resolution to .5 arcseconds
    regardless of the size of the scope if you don't have adaptive optics.
    
    
    Although adaptive optics is the preferred method of dealing with
    atmospheric distortion if you have a lot of money, there are simpler
    techniques that can achieve close to the same diffraction-limited
    results. 
    
    In particular, a class of video-based imaging techniques called "short
    exposure imaging" can be used with ordinary telescopes. One of those,
    amusingly called "lucky imaging" is quite straightforward and has been
    used to get near-diffraction-limited images of satellites and other
    objects. 
    
    Basically, the idea of lucky imaging is that the atmospheric
    distortions that limit resolution will, every now and then, "flatten
    out" in front of a telescope for several milliseconds and give a
    diffraction-limited glimpse of the target. So you take a video of the
    object, brew a big pot of coffee, and step through the video frame by
    frame and pick out the best images.  There are useful refinements, but
    that's the idea.
    
    See
    
    Ron Dantowitz, Sharper Images Through Video.
    Sky & Telescope, Vol. 96 No. 2, August 1998. 
    
    Ron Dantowitz, Scott W. Teare, Marek Kozubal. Ground-Based High
    Resolution Imaging of Mercury.
    Astronomical Journal, Vol 119 no. 6, June 2000. 
    
    http://en.wikipedia.org/wiki/Lucky_imaging
    
    
    Another short-exposure technique that requires more computational
    horsepower than lucky imaging to produce images is speckle imaging:
    
    http://en.wikipedia.org/wiki/Speckle_imaging
    
    
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