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    Re: GPS shortcomings.
    From: Fred Hebard
    Date: 2005 Jun 8, 17:40 -0400

    Could you comment on the resurgence of Loran?
    On Jun 8, 2005, at 3:52 PM, Richard Langley wrote:
    > GPS IS monitored for integrity but by WAAS! The problem WAS detected
    > by WAAS
    > and the offending satellite was marked as "do not use." Consequently
    > WAAS
    > users were protected from this anomaly.
    > -- Richard Langley
    >    Professor of Geodesy and Precision Navigation
    >    Fellow of The Institute of Navigation
    > On Wed, 8 Jun 2005, Lu Abel wrote:
    >> George and list:
    >> There's mention of this failure (due to the failure of the atomic
    >> clock
    >> on one of the satellites) in
    >> www.ion.org/sections/southcalifornia/
    >> lavrakas_civil_gps_monitoring.ppt
    >> I was rather surprised to learn that there is NOT continuous
    >> monitoring
    >> of the GPS system for integrity of its positioning information, given
    >> that there's a whole new generation of air traffic control that's
    >> going
    >> to be based on GPS...
    >> Lu Abel
    >> George Huxtable wrote:
    >>> I know that references to GPS are discouraged, if not forbidden, on
    >>> this
    >>> list. But I wonder if a note about GPS shortcomings would be more
    >>> acceptable?
    >>> I've just received a leaflet from the British Lighthouse authorities,
    >>> pushing for use of the new Loran-C transmitter at Rugby, England.
    >>> In which is the statement-
    >>> "GNSS systems themselves also suffer occasionally from undetected
    >>> failures;
    >>> for example, a satellite clock error on 1 January 2004 gave rise to
    >>> errors
    >>> in measured positions of up to 45 kilometres in Western Europe for a
    >>> period
    >>> of some 3 hours, resulting in onboard navigational failures."
    >>> I hadn't heard about that event, which sounds rather serious. Is it
    >>> common
    >>> knowledge? Can anyone offer further details?
    >>> It wouldn't have affected me. I would have been by the fireside on
    >>> that day.
    >>> George.
    >>> ================================================================
    >>> contact George Huxtable by email at george@huxtable.u-net.com, by
    >>> phone at
    >>> 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1
    >>> Sandy
    >>> Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    >>> ================================================================
    > =======================================================================
    > ========
    >  Richard B. Langley                            E-mail: lang@unb.ca
    >  Geodetic Research Laboratory                  Web:
    > http://www.unb.ca/GGE/
    >  Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506
    > 453-5142
    >  University of New Brunswick                   Fax:      +1 506
    > 453-4943
    >  Fredericton, N.B., Canada  E3B 5A3
    >      Fredericton?  Where's that?  See:
    > http://www.city.fredericton.nb.ca/
    > =======================================================================
    > ========

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