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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction near the Horizon ? Ob servation vs. Calculation
From: Brad Morris
Date: 2013 Apr 6, 15:10 -0400
From: Brad Morris
Date: 2013 Apr 6, 15:10 -0400
Marcel
With all due respect ....
You indicated that my pressure and temperature procedure is wrong.
I asked for you to show the procedure you use, with a worked example.
You responded without a procedure. The procedure is critical for understanding.
Put your procedure & numbers on a piece of paper. Submit it to the group.
Brad
On Apr 6, 2013 2:50 PM, "Marcel Tschudin" <marcel.e.tschudin@gmail.com> wrote:
Hi Brad, All your mentioned equations are approximations. It really depends on the accuracy one wants to achieve and whether this accuracy is really necessary or not. If one wants really to be exact, it is in this context actually not the radius of the earth which is of interest, it's rather the earth's radius of curvature at the location of the observer. Because the earth's shape is approximately an ellipsoid this radius of curvature depends on latitude and also on the azimuth, except at the poles. If you do not require this accuracy you can use any other less accurate mean earth radius which in the context of calculating dip are likely to be completely sufficient. Regarding the pressure and temperature dependency of refraction here some further explanations: The scaling factor (P/1010)/(T/283) adjusts the refactivity property of air, n, and as a consequence of it also the refraction resulting from it. However, the cause for light rays being bend in the atmosphere are temperature-GRADIENTS. The parameter k is introduced to describe in a simplified model the bended ray for terrestrial refraction and dip. From observations one obtained then typical values for it. Marcel
