NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction correction
From: Marcel Tschudin
Date: 2009 Jun 20, 20:08 +0300
All those formulae and calculations, like those from Auer Standish, are based on the standard atmosphere which assumes for all of the troposphere a constant temperature gradient of -6.5°C/km. This provides sufficiently accurate results for altitudes above 3 to 5 degrees above the horizon. Don't be surprised if your results won't work for observations done below this limit. The standard atmosphere has been used for calculating refraction since at least the 1950s; only the calculation procedures have changed in the mean time. Assuming the standard atmosphere for all of the troposphere is actually incorrect (despite that it delivers good results for higher altitudes or for approximate times of rise and set). The temperature profile in the lower part of the troposphere, i.e. in the Planatary Boundary Layer which extends to about 2km above the surface, behaves completely different; it follows a diurnal cycle. In a simplified way you can compare the diurnal changes of the temperature profile in the lowest about 2km like a pendulum having somewhere around 2km height a constant temperature (pivot); at the bottom end of it, corresponding to the temperature at the surface, the pendulum follows the day/night-cycle.
Yes, I'm still working on it, since 2005, encountering endless problems to be solved. All this in order that one day an improved estimation of the refraction below those 3 to 5 degrees may hopefully be found.
Marcel
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From: Marcel Tschudin
Date: 2009 Jun 20, 20:08 +0300
On Sat, Jun 20, 2009 at 6:14 PM, P H wrote:
I assume that this gives results very similar to the paper of Auer and Standish, to which Frank Reed kindly placed a link in one of his posts back in 2005.
All those formulae and calculations, like those from Auer Standish, are based on the standard atmosphere which assumes for all of the troposphere a constant temperature gradient of -6.5°C/km. This provides sufficiently accurate results for altitudes above 3 to 5 degrees above the horizon. Don't be surprised if your results won't work for observations done below this limit. The standard atmosphere has been used for calculating refraction since at least the 1950s; only the calculation procedures have changed in the mean time. Assuming the standard atmosphere for all of the troposphere is actually incorrect (despite that it delivers good results for higher altitudes or for approximate times of rise and set). The temperature profile in the lower part of the troposphere, i.e. in the Planatary Boundary Layer which extends to about 2km above the surface, behaves completely different; it follows a diurnal cycle. In a simplified way you can compare the diurnal changes of the temperature profile in the lowest about 2km like a pendulum having somewhere around 2km height a constant temperature (pivot); at the bottom end of it, corresponding to the temperature at the surface, the pendulum follows the day/night-cycle.
Yes, I'm still working on it, since 2005, encountering endless problems to be solved. All this in order that one day an improved estimation of the refraction below those 3 to 5 degrees may hopefully be found.
Marcel
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Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
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