Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Refraction correction
    From: Peter Hakel
    Date: 2009 Jun 20, 08:14 -0700
    The Explanatory Supplement to the Astronomical Almanac gives the Saastamoinen Formula.  I thought that the "low-precision" refraction formula (which immediately follows in the text) was adequate for celestial navigation purposes.  Perhaps I was wrong, especially when it comes to lunar and other distances.

    ---- begin paraphrase ----
    This formula, valid for zenith distances down to 70 degrees, was devised by Saastamoinen (1972), and it is equivalent to the refraction tables in The Star Almanac.  Given the observed zenith distance, z0, the temperature (Kelvin), pressure (mb), and partial pressure of water vapor (see below), (T0,P0, Pw0), the refraction for a wavelength of 574 nm, (i.e., visible light), and for an observer at sea level is

    16".271 * Q * tan z0 * ( 1 + 0.0000394*Q*tan^2 z0 )  -  0".0000749 * P0 * ( tan z0  +  tan^3 z0 )

    where Q = ( P0 - 0.156*Pw0 ) / T0,
    and Pw0 = Rh * ( T0 / 247.1)^18.36, with Rh being the relative humidity.

    Saastamoinen gives correction tables for other wavelengths and heights above sea level.

    ---- end paraphrase ----

    I assume that this gives results very similar to the paper of Auer and Standish, to which Frank Reed kindly placed a link in one of his posts back in 2005.


    Peter Hakel



    --~--~---------~--~----~------------~-------~--~----~
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

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

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

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

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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