[gps-talkusers] A little on WAAS
- From: "Chip Orange" <Corange@xxxxxxxxxxxxxxx>
- To: <gps-talkusers@xxxxxxxxxxxxx>
- Date: Wed, 21 Jul 2004 16:48:09 -0400
Since someone asked me off list what was WAAS, here's a quick
explanation:
Take some permanent ground stations with GPS receivers and scatter them
around the area you want to cover (in this case North America). Program
each one of them with their exact latitude and longitude. Now, have
them constantly use their GPS receivers to compute their lat/lon, and
then compare it against what they *know* it to be. It's going to be off
by a little bit because of things like the weather, the ionosphere, etc.
They make adjustments to the mathematical algorithms used by the GPS
receivers so that the results come out to match their known position
exactly. They then send these adjustments to a master WAAS satellite.
It in turn rebroadcasts to all receivers the information from each
station, and says something like:
Hey, receivers in the San Francisco California area, you need to adjust
your calculations right now by x, y, and z.
These slight little adjustments make the difference between 15 meter
accuracy and 3 meter accuracy. It may take the WAAS satellite up to 5
minutes to run through its complete list of ground stations, so that's
why at first, you don't have a WAAS lock until your receiver has heard
its location.
EGNOS will work in a compatible way in Europe.
Unlike the other GPS satellites which constantly circle the Earth, the
master WAAS satellites are in geo synchronous orbit over the equator, so
you have to have a clear view to the south in order to pick up their
signal. If you happen to be on the north side of a mountain, this might
be a problem.
Hth,
Chip
Chip Orange
Database Administrator
Florida Public Service Commission
Chip.Orange@xxxxxxxxxxxxxxx
(850) 413-6314
=20
Other related posts:
- » [gps-talkusers] A little on WAAS
