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
    Low Alt Refraction Re: USCG Student Example for Low Altitude
    From: Antoine Couëtte
    Date: 2013 Apr 28, 06:21 -0700

    http://fer3.com/arc/m2.aspx/USCG-Student-Example-for-Low-Altitude-Tschudin-apr-2013-g23711


    Hello Marcel,


    Please find here-after various Values for Refraction published for 0° Apparent Height. The applicable environmental conditions are also given whenever available.


    * US/UK NA for the YEAR 1983 (1010 mb, T = +10°C) -34.5'

    * French Ephémérides Nautiques for the Year 1981 (carefully rechecked 760 mm Hg, T = +10°C) -33.80'

    * French Introduction aux Ephémérides Astronomiques 1997 (+15°C, 1013.25 hPa, Wavelength 0.590 micro meter, Water pressure = 0 Pa, Latitude 45°, Altitude 0 m) 32'57.971"

    * Ephémerides Astronomiques 1990 (Radau Theory for 1000 mb and 0°C) -36'36"

    * Explanatory Supplement Sep. 1977 (unspecified conditions) -34'

    * Explanatory Supplement 1992 : same as E.S. 1997

    * André Danjon's Astronomie Générale 1980 (0°C, 76 cm Hg, Wavelength 0.575 micrometer) -37'52"

    * Jean Meeus' Astronomical Formulae for Calculators 1988 (unspecified conditions) -0.34'

    * Jean Meeus' Astronomical Algorithms 1991 (1010 mb and +10°C) gives Bennett's formula which is believed to be accurate to +/- 0.07' and yields -34.48' (and with an additional correction bringing its overall believed accuracy to +/- 0.9" it yields -34.50'). It is therefore quite likely that when deriving his (quite "magic") Formula M. Bennett was targeting the US/UK NA values indicated here-above.

    When appropriate I leave upon you the task of reworking these different results into the very same environmental reference (e.g. 1010 mb and +10°C) so that you can get a good feeling of the Refraction Values dispersion at 0° apparent altitude. My guess is that they all should match the US NA -34.5' value to within +/- 1'. Let me know your results.

    Hope it may help you better this time.

    Best Friendly regards

    Kermit

    pS : As you can observe the so called "European" Standard conditions (+15°C, 1013.25 hPa) were used only in the French Introduction aux Ephémérides Astronomiques.

    Such "standard" conditions (+15°C, 1013.25 hPa) are also used into the ICAO Standard Atmosphere model used in Aviation. And ...

    ... if you do not them by heart day AND night, .. don't ever EVER expect to be granted cockpit access ! :-)
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]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