Re: Caught ISS on the Sun, but ....

From: David Tiller (dtiller@captechconsulting.com)
Date: Fri Mar 25 2011 - 15:09:44 UTC

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    Giuseppe,
    
    I believe the effect you are seeing is the result of your video camera taking interlaced video. With interlaced readout, every even line is read, then every odd line (or vice versa). Because the ISS is moving very quickly with regard to the video frame, you get two images - one showing the position of the ISS at the time of even line readout and one showing the position of the ISS at odd line readout. Instead of 6 full frames every 40 mS, you've actually got 12 partial frames every 20mS with frames 1&2 interposed, 3&4 interposed, etc.
    
    See: http://en.wikipedia.org/wiki/Interlaced_video
    
    If you know the delta-T between readouts you can calculate the velocity of the ISS in degrees/sec given the angular width of the sun (which is calculable for the time of the image).
    
    --
    David Tiller
    Lead Consultant/Architect | CapTech
    (804) 304-0638 | dtiller@captechconsulting.com
    
    ________________________________________
    From: seesat-l-bounces+dtiller=captechconsulting.com@satobs.org [seesat-l-bounces+dtiller=captechconsulting.com@satobs.org] on behalf of Giuseppe N. Gerbore [giuseppegerbore@virgilio.it]
    Sent: Friday, March 25, 2011 10:38 AM
    To: seesat-l@satobs.org
    Subject: Caught ISS on the Sun, but ....
    
    I caught ISS crossing the Sun, but ISS is "double".
    There are six frames equally spaced about 40 ms, all with double image . Fps was 25.
    This is one:
    
    http://img846.imageshack.us/i/20110325isscrossingthes.png/
    
    Any hints? My cam may reach 50 fps if necessary.
    
    Giuseppe
    
    Giuseppe Gerbore, Modena, Italy
    
    4438'14"N, 1054'05"E, 57m
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