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
    Re: Noon Sun sights, Jamestown RI, this Sunday, Aug. 25
    From: Antoine Couëtte
    Date: 2013 Sep 9, 03:49 -0700

    RE : http://fer3.com/arc/m2.aspx/Noon-Sun-sights-Jamestown-RI-this-Sunday-Aug-25-Stuart-aug-2013-g25027 and

    RE : http://fer3.com/arc/m2.aspx/Noon-Sun-sights-Jamestown-RI-this-Sunday-Aug-25-Stuart-sep-2013-g25042

    Hello Robin, and Hello to all,


    A bit late ... :-(


    Thank you very much for your SUN LAN Sight's from Aug 25th, last.

    I have reworked them (both the full 14 Sight set and 13 Observation set which excludes the 1st observation) through a 7th order regression fit.

    There are minor differences between our "starting data".

    The most significant one concerns the Combined Height Correction most probably because of a slightly different dip value used in my computations. I have used combined values (computed for each observation) very close to 10.0' , vs. your +10.1' fixed value. It has a quite negligible effect on the Longitude determination and brings up the Computed Latitude 0.1' closer to the true Latitude than your own determination.

    I also accurately compute ΔT culmination-transit and I find its value equal to 9.2s (vs. your 9.6s determination) It makes sense since you probably used the classical 1st order Formula :
    " ΔT culmination-transit (s) = 48/π * (tan Lat - tan Dec) * ( d/dt Lat ['/hour] - d/dt Dec ['/hour] ) "
    while I have used a more accurate 7th order determination.

    ******

    Full results given in the enclosures. Some comments here-under :

    *******

    With the 14 Sight set, get :

    True Position 0’5 North and 1.1’ West from Computed Position.
    SUN Local Time Transit 12h47m29.5s ***
    OBS LAT=N 41:26.4 *** OBS LON=W 071:22.9 ***
    √(σ[d2/n])=0.4 NM ***
    VALID+/-0.43 h.mm around Culmination Time *** Valid UT SPAN (16.04-17.30) ***
    e.T’ / e.H’ ≤ 3.9 *** 1σ EST LAT ERR 0.4’ *** 1σ EST LON ERR 1.5’ ***
    ΔT culmination-transit = -9.2s

    In other words :

    *** the 1σ Longitude error is 1.5' vs. your Monte Carlo 1.75' determination. I am using the (small) 14 Observation sample set while you are using a 10,000 simulated observation set. This should explain the (small significance) difference between our results. And,
    *** the 1σ Latitude error is 0.4' vs. what would seem a significantly (much) higher 1σ value of yours. A good thumb rule is to remember that the Latitude 1σ error is (almost) equal to the heights 1σ error, i.e. 0.4' (or 0.4 NM) in this 14 sample case.


    *******

    Without the first observation, get :

    True Position 0’3 North and 1.4’ East from Computed Pos.
    SUN Local Time Transit = 12h47m39.5s ***
    OBS LAT=N 41:26.6 *** OBS LON=W 071:25.4 ***
    √(σ[d2/n])=0.3 NM ***
    VALID+/-0.43 h.mm around Culmination Time *** Valid UT SPAN (16.04-17.30) ***
    e.T’ / e.H’ ≤ 3.9 *** 1σ EST LAT ERR 0.3’ 1σ *** 1σ EST LON ERR 1.0’ ***
    ΔT culmination-transit = -9.2s


    *******

    To conclude :

    - The Longitude determination is quite sensitive to one single observation which SEEMS to be an "outlier". The Computed longitude shifts from W 071:22.9 with 14 observations into W 071:25.4 with 13 Observations. Interestingly enough, with the 14 observation set the error of the Computed Longitude (1.1') is equal to just 0.8σ since 1σ=1.5', while with the 13 observation set the error of the Computed Longitude (1.4') is equal to 1.4σ since 1σ=1.0' in this case.

    - The Latitude determination is much more insensitive to any so-called "outlier". It is no surprise that most accurate Latitude determination is obtained with the 13 observation set : 0.3' error in this case i.e. just 1σ since 1σ=0.3'. With the 14 Observation set, the Latitude determination is still quite good : 0.4NM, again equal to 1σ since 1σ=0.4' in this set.

    - It might be questionable to reject the first observation as a definite outlier. This thrilling subject has been addressed at lenght in NavList a few years ago. You actually did not reject it in your Monte Carlo simulation and I think that you are fully right in this respect.

    ******

    It was very interesting Robin, to independently work your own numerical results. Thank you again for sharing with our NavList Community this nice LAN example altogether with your Monte Carlo simulation and interpretation of these sights.

    Best Friendly Regards

    Antoine M. "Kermit" Couëtte

    ----------------------------------------------------------------
    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?

    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