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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction at the horizon.
From: Marcel Tschudin
Date: 2008 Mar 19, 21:07 +0200
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 To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---