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    Re: Q: how to calculate refraction at higher altitudes on land?
    From: Dov Kruger
    Date: 2002 Feb 28, 10:40 -0500

    At high angles (above 45 or so) you will have so little refraction in
    the first place that any reduction in it won't make a significant
    difference with what I originally said. You can just do your atmospheric
    correction and that's more than it deserves. But at the lower angles,
    the normal correction for pressure will presumably be too great, because
    the reason the pressure is low is that you are high, not because your
    whole region is experiencing low pressure.
    In the worst case, consider you are looking down at the horizon. Near
    the horizon, your line of sight is passing through sea-level air.
    Halfway, it is passing through air at half your altitude. Since the
    correction is small in any case, why not just try to divide it in half
    and use that? You know the upper bound (no pressure correction) and the
    lower bound (full pressure correction) so you know exactly how bad your
    assumption can be.
    Why not send us the raw data when you do it so we can take a look?

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