Accuracy, How bad?

[Guest Kerry]

Been lots of discussion on how good accuracy is (or percieved to be) but how bad can it get?

 

Accuracy specs are stated as so many metres @95% and also @99.99% but there's always been that other open ended 0.01% chance/risk of something?? Nothing is perfect and GPS is no exception.

 

A few hours before midnight July 28 (UTC) an anomaly with the timing/clocks occurred on satellite 22. The day after users were querying/reporting position errors of around 90-92 nautical mile at that time.

 

Some independent analysis of recorded data from receivers in Canada, the U.S and Pacific at the time of the anomaly have confirmed these horizontal position errors at around 200km's.

 

What is also interesting is that even though the Master Control Station at Colarado Springs would have been tracking 22 the anomaly appeared to go undetected for quite some time. Even after 22 was set unhealthy there appeared to still be some issues? The way it reads is that WAAS enabled receivers appear to have not picked it up either.

 

So any positions which were using 22 in the constellation between about 22:30 and 23:58UTC July 28 (what's that make it Saturday afternoon U.S west coast time) could have some strange positions?

 

Cheers, Kerry.

 

[This message has been edited by Kerry (edited 25 August 2001).]

[Guest GeoForse]

So how does one find about such anomalies. Can you be notified directly by e-mail. Also, How often do these happen?

[Guest Kerry]

Anomalies such as this particular one are rare but goes to show just what can occur. There's no way these types of events will have notification until after the event and in general will only state that Satellite X was unavailable for a time frame due to what ever caused the problem. The general effect of the problem will also not be part of this service.

 

As well as unplanned events scheduled outages/maintainance shutdowns/forecasts are also made available on a daily basis.

 

All civilian GPS matters are handled by the USCG navigation center http://www.navcen.uscg.gov/

 

The GPS Active NANU's and STATUS can be viewed at the above link as required or subscribed (bottom of USCG front page).

 

Cheers, Kerry.

 

 

[This message has been edited by Kerry (edited 27 August 2001).]