NavList:
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
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
