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Re: Q: how to calculate refraction at higher altitudes on
From: Chuck Taylor
Date: 2002 Feb 28, 12:18 US/PACIFIC
From: Chuck Taylor
Date: 2002 Feb 28, 12:18 US/PACIFIC
> I am specifically trying to determine the elevation of my house. > > I have a high quality Chelsea barometer, ... > > Given these constraits and tools, can I get a better estimate of > my elevation? Dan, I would recommend using your barometer instead of your sextant. Obtain the sea level reading either from radio/TV/internet or by driving down to the water, then compute the altitude from that. I did a bit of research, and came up with a site that talks about constructing an electronic barometer: http://davidbray.org/onewire/barometer.html For calibrating the barometer, he gives the following formula: absPress = exp((log(1 - 6.87324e-6 * altitude) * 5.256)) * seaLevPress where "absPress" is the pressure at your elevation. Here "log" means "natural log". Solving for altitude, I came up with altitude = 145491.8*(1 - exp(log(absPress/seaLevPress)/5.256)) That is for pressure in inches and altitude in feet. It should be a piece of cake to program that on one of your HP calculators. A linear approximation would be about 0.001065 inches of pressure per foot of altitude. There is a link on that page to a table which gives values for every 50 feet of altitude. Chuck Taylor Everett, WA, USA