NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2024 Jun 6, 05:42 -0700
Dear All,
Further to my last contribution on this subject, I think that there is an adequate solution - at least adequate under normal atmospheric conditions - to my early query : Any available existing available theory to pre-compute refraction between 2 nearby points knowing Positions and Altitudes of departing and arrival points ?
The attachment gives 2 solid references from which a simple computation method is derived and which is reliable, at least under "standard" atmospheric conditions.
Such numerical approximation can be summarized as follows:
At low altitudes, the vertical elevation between 2 [nearly] horizontal points at a finite distance is equal to about 8% of their distance in NM.
As shown in the enclosure, what is amazing - to me at least - is that when we subtract such 8% from the unrefracted sea horizon Dip - Dip’ Unrefracted = 1,925 √h m we obtain exactly the refracted horizon Dip - Dip’ Refracted = 1,771 √h m - "Official" [worldwide] figure for standard atmosphere.
No age to keep learning !
Enjoy !
Kermit
