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    Q: how to calculate refraction at higher altitudes on land?
    From: Dan Allen
    Date: 2002 Feb 27, 21:40 -0800

    I was out shooting sights with a variety of sextants yesterday and today in my 
    backyard, a very enjoyable activity.  In order to get
    the best sights I measured the outside air temperature and pressure using my 
    Casio watch, you know, the one that says that noon is
    PM... ;-)
    Anyway, the question is, how does one calculate refraction at higher altitudes 
    on land?  Do I just use the actual barometric
    pressure or do I somehow factor in elevation explicitly?
    It is my understanding that the more atmosphere, the more refraction, hence 
    higher elevations have less pressure and thus less
    refraction.  Bowditch and other sources do not say much about refraction as a 
    function of elevation above sea level.  I did notice
    one comment about Air Almanacs having extra columns in their refraction tables 
    to allow an elevation to be entered, but I do not
    have an Air Almanac to check on this.
    My guess is that if refraction is stricly due to atmospheric thickness, the 
    barometric pressure is sufficient, but if there are
    geometrical aspects to refraction (which I know there are since there is no 
    refraction for a body directly overhead), then elevation
    much above sea level needs to be accounted for separately from barometric 
    pressure.  The question then is, by how much?
    Does anyone know the story about high altitude refraction?
    Daniel K. Allen
    Navigate | Calculate | Communicate

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