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    Re: GPS shortcomings.
    From: Richard B. Langley
    Date: 2005 Jun 8, 16:52 -0300

    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---.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---.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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