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Has anyone in your area sold a house or property lately?  They may have
had a survey done.  This should have an elevation on it for a nearby
monument.  Then you work from there with your sextant(s) and an
artificial horizon.  Just a suggestion ...  The neighbours might be
keen to participate in the project.

John Kabel
London, Ontario

> I am specifically trying to determine the elevation of my house.
>
> The topographic maps of my area are decades old.  They do not show
> our streets or houses, and in fact the area has been graded to some
> extent as well, so even finding my exact location via GPS and then
> looking on the map only gives a ballpark figure.
>
> Since SA has been turned off, the GPS gives a range of elevations
> from 580 feet to 650 feet.  The Garmin GPS 3 tends to wander over
> this range.  I am trying to get a better value.
>
> I have a high quality Chelsea barometer, a Garmin GPS, and many
> sextants.  I have high mountains behind my house, lots of clouds,
> and the only kind of horizon I'll ever see is an artificial one.
> In the winter, the sun comes up behind the mountain at about 11AM
> and goes down about 12:30PM!
>
> Given these constraits and tools, can I get a better estimate of
> my elevation?
>
>
> -----Original Message-----
> From: Navigation Mailing List
> [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Dov Kruger
> Sent: Thursday, February 28, 2002 7:41 AM
> To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
> Subject: Re: Q: how to calculate refraction at higher altitudes on land?
>
>
> 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

   

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