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
    Name or NavList Code:
    Email:
       
    Reply
    Single-body fix method
    From: Christian Scheele
    Date: 2009 Aug 5, 21:09 +0200

    Can anybody point me to an open-access source dealing with Byrd's and Weems'
    attempts to make use of the "single-body fix method"? I believe Weems
    undertook these tests to aid Byrd in his air navigation in polar regions.
    
    The "single body fix method" has been the subject of one, perhaps several
    threads on this site, which I have only been paying attention to recently.
    James N. Wilson has also written an article about it which is on the ION CD,
    but I am not familiar with the work as I do not have a professional interest
    in celestial navigation or any of the natural sciences. I understand that
    the method's weakness are the requirement of knowledge of the body's azimuth
    and the limitations it places on the fast-moving observer. I saw a
    digestible  -speaking in very personal terms - description of it complete
    with a derivation of the required formulae in the online ION Newsletter in
    an article about half way down the page by Joe Portney entitled "Portney's
    Corner: The Lost Sub Quick Fix". Here is the adddress:
    http://www.ion.org/newsletter/v11n1.html
    A follow-up reader's letter under the heading "Pondering Portney's
    Ponderables"  in the subsequent online issue claimed/reported on errors that
    appeared in an embedded diagram and in the derivation of the formulae in the
    earlier article. The web address at which this second article can be found
    is:
    http://www.ion.org/newsletter/v11n2.html
    The first article merely alludes to the Byrd and Weems trials involving this
    procedure, involving sights of the sun taken through "the open hatch of a
    seaplane."
    
    I am still pondering the method. To this end I am reading a chapter in
    Charles Cottter's "The Elements of Navigation" on the subject of "rates of
    change" (of celestial bodies' altitudes), although this particular
    description is limited to meridian observations and is only indirectly
    related to the subject of the "single-body fix method", Cotter's objective
    here being the determination of the sun's maximum altitude. At present I am
    unsure as to why Cotter puts observed changes in altitude of a celestial
    body, a function of the combination of movement of the celestial body and
    the observer's own movement, into a formula that is a "partial integral" (my
    own term), covering the rate of change in one minute of time in one linear
    equation, rather than a "true" integral function, but maybe that's because
    we are talking about a slow-moving observer (on a ship) and it is therefore
    good enough to use an approximation. In any event, I imagine that practical
    application of the method (if, indeed, it is practical at all), where the
    period of observation of a body's rate of change may be a minute or a half a
    minute (for as much as I know), must by necessity involve the "partial",
    rather than the "real" derivative, but I think this is a different
    consideration. To those readers who are familiar with this cited chapter, is
    the method which Cotter explains an approximation as I suspect, or is it
    complete and to be used without reservation as suggested?
    
    Christian Scheele
    
    
    --~--~---------~--~----~------------~-------~--~----~
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To , email NavList-@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    NavList ID 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