NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction
From: Marcel Tschudin
Date: 2005 Aug 8, 20:28 +0300
From: Marcel Tschudin
Date: 2005 Aug 8, 20:28 +0300
Clive wrote
The following is one I use,Ref = Tan (90-Altitude - 0.999139 * Altitude - (7.31 / (Altitude + 4.4)))between -20 < Air Temp < +40, and 970 <air pressure mbs < 1050or else use the correction below for abnormal temperature and PressureAbn = (( Baro Pressure - 80 ) / 930) * (1 / ( 1 + 0.00008 * (Refraction + 39) * (Temperature - 10))),using mbs,deg celsius and deg Altitude.Refraction = Ref * Abn and True Altitude = Observed Altitude - Refraction
Does anyone of you know where this correction for
abnormal condition comes from?
What is actually ment with "abnormal"? As an
example, the standard atmosphere also has temperatures below -20°C and air
pressures below 970 mBar above a certain height, but this I would consider
rather "normal". Could it be that the abnormal conditions refer to sea level
conditions?
Thanks Marcel
