[STL Geocaching] Re: New cache, needs boat

  • From: "Paul Becker" <pebecker@xxxxxxxxxxxx>
  • To: <geocaching@xxxxxxxxxxxxx>
  • Date: Tue, 9 Apr 2002 15:27:27 -0500

>>From: Dan Eubanks
>>WAAS stands for Wide Area Augmentation System. This is a series of ground
based antenna signals that
>>are placed in North America. They are similar to GPS signals. If your GPS
Unit is set up to receive
>>WAAS signals then your accuracy goes from about 20' to 2' on a good day.
This system is still under
>>development and promised to get better as time goes by. Soon all GPS units
will be WAAS capable as
>>a standard feature.

Minor nit-pick...
WAAS uses 25 ground-based reference stations for error measurement data
collection ONLY.  These stations do not transmit the actual WAAS signal as
received by the GPS receivers.  They measure pseudorange errors for each
satellite as well as other sources of timing error (such as ionospheric and
tropospheric signal propogation delays). The measurements are sent to a
master control station, where they are processed and transmitted up to a set
of geostationary satellites which broadcast the actual WAAS signals to all
listening WAAS-capable receivers.

For it to be most effective, though, the GPS must be within a region
serviced by at least one of the monitoring stations.  Why?  Because
ionopheric delays are constantly changing and relatively local in nature.
It is possible to have MORE error using WAAS than without it.

This is unlike the DGPS (RTCM) network operated by the Coast Guard, which
require a DPGS receiver and a DGPS-capable GPS.  In addition, you must be
within range of a DGPS transmitting station (there's one in St. Louis).  In
the case of DGPS, the ground station both measures the errors AND transmits
the signals.

I told you I was just nit-picking, but I thought someone might be
interested.  For more information:
http://wwws.raytheontands.com/waas/
http://waas.stanford.edu/tmslive/

Yes, I do wear a propeller cap.
Paul





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