Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Name or NavList Code:
    Atmospheric refraction high above Sea Level
    From: Antoine Couëtte
    Date: 2024 Jul 3, 00:05 -0700


    In this very interesting recent post of yours summarizing all "your" Refraction Formulae, my attention got caught by the following one :

    [Quote]" Correction for height above sea level. htObs is the observer's height above sea level in km:

      refx = refx * exp(-htObs / 9.5) " [Unquote]

    Since I never - so far ... - had to deal with refractions applicable to high elevated spots on the Earth, I never studied the subject in close detail.

    (1) - Let's start on an example :

    From a spot at 25,000' AMSL in standard atmosphere :

    htObs = 7.620 km , OAT = -34.5 °C , QNH = 1013 mb , "onsite" pressure (QFE) = 376 mb

    (1.1) - I would compute Standard Astronomic Refraction as follows :

    Temperature correction factor : Tcf = ( 273.15 + 10 ) / (273.15 - 34.5) = 1.1865

    Pressure correction factor : Pcf = QFE / 1010 = 376 / 1010 = 0.3723

    "T & P" combined  correction factor : "Ctp" = Tcf * Pcf = 0.4417

    (1.2) - On the other hand : " exp(-htObs / 9.5) " = 0.4484, quite close from the previous line value ... so , instead of being an additional correction factor - i.e. on top of "Ctp" - as I first understood it upon reading your initial post, this exponential correction factor is probably the fully integrated correction factor designed to entirely replace the former traditional "T & P" calculation, no ?

    Thanks for this interesting piece of information.

    Then, from which AMSL htObs - and above - do you think we can validly start using it ?

    Please advise,


    Browse Files

    Drop Files


    What is NavList?

    Get a NavList ID Code

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.

    Email Settings

    NavList ID Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site