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    Re: Refraction at the horizon.
    From: Marcel Tschudin
    Date: 2008 Mar 19, 21:07 +0200

    A reply to George's comment:
    Before I mentioned "ducting" only in the context of verifying the
    program. I tried to show that for verifying the program we looked at
    all sorts of tricky cases. The profile used in this calculation to
    derive a transfer function for refractions at large ZDs was the very
    well behaved standard atmosphere which produces no strange anomalies.
    The only special thing in it is the observer being very high up,
    almost at the tropopause. One of the test case with which we compared
    our programs was similar, it also had the observer at 10 km height
    otherwise also a "normal" lapse rate profile. The differences we had
    were much less than those resulting from the exponential behaviour.
    George mentions:
    "Gravity has reduced by only one part in 300 from the surface to 10 km
    up, so it's hard to see that having much effect, except at enormous
    heights, where no air remains."
    The effect from gravity is expected to be larger since it appears in
    the power. I really don't know the possible reasons for it; may be
    gravity is one of them. From tests done on the program it looks like
    the effect is "real", but not knowing the cause I can't exclude the
    program. May be someone else would give try. How about you Frank?
    Navigation List archive: www.fer3.com/arc
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