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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Q: how to calculate refraction at higher altitudes on land?
From: Dov Kruger
Date: 2002 Feb 28, 10:40 -0500
From: Dov Kruger
Date: 2002 Feb 28, 10:40 -0500
Oops! Dan, 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? cheers, Dov