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Subject: Q: how to calculate refraction at higher altitudes on land?
From: Dan Allen (danallen46@XXX.XXX)
Date: Thu Feb 28 2002 - 00:40:02 EST
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?
Thanks,
Dan
Daniel K. Allen
mailto:danallen46@XXX.XXX
http://home.attbi.com/~danallen46/
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