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    Re: Sextant accuracy and possibility of future improvement
    From: Paul Dolkas
    Date: 2016 Jul 24, 21:23 -0700

    I’m going to disagree.  If you are flying in strait and level flight, there is no question which way is up. The slight perturbations to the local gravity field caused by the fact that the earth isn’t a perfectly round homogenous sphere are in the noise level as far as CN (AN?) is concerned. But any acceleration from the throttle is going to show up as a tilting forward (or aft) of the perceived gravity vector. Since we are talking in minutes and seconds of a degree, it isn’t going to take a lot of this to make a difference. Same with a banked turn.

     

    This is probably why aircraft bubble sextant are really only designed for 1-2 minute accuracy: 1) because of the uncertainty in the vertical caused by aircraft motion, and 2) because, as Frank Reed pointed out, the sub-minute accuracy of nautical sextants was driven by the need to perform lunars as a chronometer check. By the time airplanes came about, no airplane navigator had to do a lunar to correct his watch.

     

    Paul Dolkas

     

    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of David C
    Sent: Thursday, July 21, 2016 10:34 PM
    To: paul{at}dolkas.net
    Subject: [NavList] Re: Sextant accuracy and possibility of future improvement

     

    I believe that it is possible to separate aircraft accelerations from gravity:

    (LINZ = Land Information New Zealand aka Lands And Survey)

    "LINZ says that understanding the height of our land is important for understanding how water will flow during a flood or storm. People commonly talk about metres above sea level as a way of describing heights, but sea level can vary at different points around the country. To give scientists and researchers consistency, LINZ has developed a new vertical datum, a reference system based on gravity.

    This has been four years in the making and has involved flying the length and breadth of the country with a specially equipped plane for gathering gravity measurements, as gravity can vary from place to place."

    For the audo on which this quote is based go to

    http://www.radionz.co.nz/national/programmes/ourchangingworld/audio/201807946/exactly-where-is-sea-level-gravity-can-tell-us

    I have no idea what technology is used and what it cost.

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