NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars barometric pressure correction
From: Frank Reed
Date: 2005 Apr 19, 20:45 EDT
From: Frank Reed
Date: 2005 Apr 19, 20:45 EDT
Bill, you wrote: "The consensus seemed to be that local-station barometric pressures were corrected to sea-level pressures before broadcast (and barometers were likewise adjusted to show sea-level pressures for their permanent location above sea level) . When using your Lunars Calculator, would it behoove the user to correct from reported sea-level pressure to local pressure?" Yes, if you're at an unusually high altitude above sea level, then you should multiply typical "weather report" barometric pressures by exp(-altitude/34,000 feet) [roughly]. Assuming you're staying in the same place, you will only have to calculate this once. For an altitude of 1000 feet above sea level, this factor would be 97.1%. This will make almost no difference --only a tenth of a minute of arc for altitudes below 20 degrees, two-tenths below 10 degrees. If you go for a sail on Lake Titicaca, the world's highest navigable lake, the factor is 69% and you'll have measurable changes in refraction at all altitudes below 70 degrees. -FER http://www.HistoricalAtlas.com/lunars
