Re: Satellite Altimeter

From: Gerhard HOLTKAMP (grd.holtkamp@t-online.de)
Date: Thu Jan 19 2006 - 16:52:06 EST

  • Next message: Steve Newcomb: "8539 obs jan 19"

    Scott Campbell wrote :
    
    >This amazing device actually finds satellite range.  A must have for every 
    >observer.
    
    >http://www.coastalbend.edu/acdem/math/sats/sat_altim.htm
    
    Looking at the respective page and the associated pdf-file explaining the math 
    behind it I ran a simulation to find out what to expect of it. I used 
    different passes of the ISS and ENVISAT and checked different arc lenghts and 
    different elevations. Plugging all these data into to the formula given on 
    the file I then found the respective height assuming the actual measurements 
    would have been done accurately.
    
    With the ISS I first tried a pass which passed close to the zenith. A 30 deg 
    arc centered at an elevation of 35 deg yielded a height of 347 km - exactly 
    the right value. A similar arc centered around the zenith position overshot 
    at 366 km, while a 20 deg arc centered around 30 deg elevation showed 310 km.
    
    The second ISS pass which didn't pass through the zenith but rather reached a 
    maximum elevation of 50 deg yielded heights around 290 km close to the 
    maximum elevation for arcs of 10, 20 and 30 deg.
    
    For an ENVISAT pass with a maximum elevation of 76 deg I got 756 km for an arc 
    close to its maximum elevation which is very close to the actual 758.7 km. 
    But a flat ENVISAT pass with a maximum elevation of 25 deg gave me a dismal 
    250 km height!
    
    Maybe re-doing the math (using spherical rather than planar geometry and arcs 
    rather than lines) will show more consistent results  - if I have a sleepless 
    and cloudy night I'll give it a thought.
    
    Actually, here is a SeeSat-L question: I have a gut feeling that an 
    experienced satellite observed would be able to estimate the height of a 
    satellite to within 50 km or so and even come up with a fair estimate of the 
    inclination by merely looking at how the satellite moves across the sky 
    (without any actual time and angle measurements). Has anyone ever done 
    corresponding experiments (at a star party, lets say)? (I remember times when 
    a Shuttle and the ISS or Mir were up in the sky in different orbits and 
    visible on the same evening. It was very obvious when they were at different 
    altitudes.)
    
    Gerhard HOLTKAMP
    Darmstadt, Germany
    
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