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Re: Refraction at the horizon
From: Andrés Ruiz
Date: 2008 Mar 14, 08:52 +0100
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From: Andrés Ruiz
Date: 2008 Mar 14, 08:52 +0100
The thermal structure of the standard atmosphere is like this:
Temperature stratify the atmosphere in layers of different density, this acts diverting the beam of light from celestial bodies.
An approximation to this fact is the well known formula for refraction:
Ro = 0.0167 / (tan (H + 7.31) / (H + 4.4) )
f = 0.28 * P/ (T+ 273)
R = f * Ro
H : apparent altitude, (sextant altitude corrected for index error and dip)
P: pressure [mb] or [hPa]
T: Temperature of the air [ºC]
But for low angles is more complicated and under abnormal situations unpredictable.
Also the meteorological phenomenon can disturb the standard refraction.
Andrés Ruiz
Navigational Algorithms
http://www.geocities.com/andresruizgonzalez
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