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    Re: GPS shortcomings.
    From: Lu Abel
    Date: 2005 Jun 8, 13:01 -0700

    Richard:
    
    My understanding of WAAS is limited, but I am under the impression that
    it is similar to differential GPS, ie, a receiver's precisely known
    position is used to create corrections to GPS's position indication.
    
    What I don't know is how widespread WAAS control receivers are.  I could
    certainly see that if a satellite's clock went awry over Europe the
    anomaly would be quickly noted.  But what about notification to someone
    trying to pick their way through some coral atolls in mid-Pacific?  Or
    on a passage from Cape Town to Australia?
    
    Lu Abel
    
    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---.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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