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