Re: OIG TLE harangue

From: Thomas Fly (tfly@alumni.caltech.edu)
Date: Fri Jun 18 2004 - 09:03:01 EDT

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    > I got the following results from the posted data using my program. Does it
    come close to your results. I wonder if I need to improve the accuracy.
    
    I don't see anything in your program run that specifies the elevation above
    sea-level (the Geoid, or whatever), so presumably your program is assuming
    sea-level.  That indeed would have a significant effect on accuracy!
    
    
    > ... and an elevation of 202.5 meters.
    
    > I should have added 31 meters to the latter, because I believe SkyMap treats
    elevation as distance above the WGS84 ellipsoid, rather than above the Geoid;
    locally, the Geoid is 31 meters below the ellipsoid:
    http://earth-info.nga.mil/GandG/wgsegm/intptW.html
    Consequently, SkyMap shows the MCC track very slightly above the center of the
    solar disk.
    
    I spent what seemed like the entire day yesterday in an email debate about
    whether or not to add or subtract Geoid heights.  By the time I'd gotten the
    other fellow on the same page as me, evidently I'd succeeded in confusing
    myself!
    
    At any rate, I believe I should have subtracted 31 meters from the elevation
    before handing it off to SkyMap, which would have slightly (further) raised the
    MCC track above the center of the solar disk.
    
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