EGS, Topex Poseidon and Four Frames...

From: Scott Tilley (
Date: Mon Aug 06 2012 - 22:46:13 UTC

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    Hi All
    Here's a couple of interesting files from obs of EGS (AJISAI) 16908 
    86-061A and TOPEX/POSEIDON 22076 92-052A two of the most beautiful 
    flashers in the sky.
    (note: the dark lines in this image are from an antenna hanging between 
    some trees...)
    The png images are small (<150kb) the FITS images are ~6.5mb.
    I share this as it shows the power of four frame method of compressing 
    video images using the four frame method used mainly by meteor observers 
    until Cees adopted it for satellite obs earlier this year.  This may be 
    of particular interest to those studying not only satellite orbits but 
    the optical characteristics of the s/c.
    The four frame method recorded as a FITS file records 10 seconds worth 
    of data in one file in four frames:
    1) the mean pixel value. (used to determine astrometic location)
    2) the standard deviation in the pixel values.
    3) the maximum pixel value in the sequence. (reveals satellite trails)
    4) the frame number in which the pixel value had the maximum value. 
    (Used to determine the precise time of a satellite track within the image)
    With this four frame image you have everything you need to determine 
    location, time and brightness of an object without needing to store raw 
    video data.
    Cees' software generates a fifth frame in a separate file used to ID the 
    satellites that pass though the FOV.  It uses the general SpaceTrack 
    catalog and the Mike McCants classified catalog to show everything that 
    should be in the FOV at any particular time. Anything passing through 
    the FOV that is not in the catalogs can be found by a manual scan 
    through the images.  An automated scan is used to grab out the 
    'interesting' classified passes or later reduction.
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