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RE: Accuracy of GPS with respect to surveys

The GPS can be operated in differential mode which allows for accuracy down
to a few centimeters.  Differential mode requires the use of a second
receiver which provides a correction to the satellite signals.  The second
signal is broadcast from a land based transmitter whose location is
accurately known.

Check with some of the local surveyors.  This differential GPS technology is
apparently in wide spread use.

Jim Key

> ----------
> From: 	George Andrews[SMTP:mauser2@erols.com]
> Reply To: 	radsafe@romulus.ehs.uiuc.edu
> Sent: 	Thursday, April 30, 1998 3:28 PM
> To: 	Multiple recipients of list
> Subject: 	Re: Accuracy of GPS with respect to surveys
> Bruce,
>     The actual number for position accuracy available to civilian
> population
> is 15 meters. The 100 meter value is based on US DOD imposed Selective
> Availability Program. Using an 8 channel serial receiver usually results
> in
> a position error of 90 to 140 feet, (personal experience). This appears to
> depend on the number of SATs locked onto. I suspect use of a 12 channel
> parallel receiver would produce better accuracy. Use of the signal from a
> digital GPS receiver and a GPS unit is said to be 5 to 10 meters.
> George Andrews
> mauser2@erols.com