Expect 'unreliable or unavailable' GPS signals

[Kevin Rooney]

Saw this on another hiker BB:

East Coast

West Coast

The testing period for the West Coast has nearly ended.

Would be interesting to know what the "test events" are.

 

[Nessmuk]

Saw this on another hiker BB:

East Coast

West Coast

The testing period for the West Coast has nearly ended.

Would be interesting to know what the "test events" are.

It's been a few years now, but a certain DoD laboratory I am familiar with ran some experiments in the Northeast that unwittingly shut down reliable GPS signals for a few hundred mile radius. It didn't last long, but long enough to get major attention at the time.

 

[psmart]

Interesting. I'm sure they'll be all sorts of theories about this one! Perhaps DoD is testing technology that could potentially interfere with GPS service? Hence the specific request to report all disturbances.

Does anyone know if the test areas are centered under specific satellites? If so, it would suggest a test on the satellite end, otherwise a ground-based test of some other equipment located at the center.

 

[Nessmuk]

Does anyone know if the test areas are centered under specific satellites? If so, it would suggest a test on the satellite end, otherwise a ground-based test of some other equipment located at the center.

The satellites are not in geosynchronous orbit, and thus you cannot be "under" any one of them for more than a short time as they traverse the sky.

 

[DougPaul]

Nothing to get excited about. Every now and then DoD conducts tests of jammers for local area GPS denial.

The purpose of such technology is to be able to deny GPS to an enemy in a war zone while keeping it usable for friendly forces and out-of-zone users. (There are currently two modes--a civilian signal on one frequency (L1 C/A) and an encrypted military signal on two frequencies (L1 P(Y) and L2 P(Y)).

It appears to be a test of an airborne jammer--see http://groups.google.com/group/sci.geo.satellite-nav/msg/c5fc369bd2a7bfc4 for an analysis.

Doug

 

[DougPaul]

Does anyone know if the test areas are centered under specific satellites? If so, it would suggest a test on the satellite end, otherwise a ground-based test of some other equipment located at the center.

No. As Nessmuk stated, the GPS satellites are not geostationary--they are in 11 hour 58 minute orbits.

Only the WAAS satellites are geostationary--and geostationary satellites have to be over the equator.

The center of the GPS denial area is the location of the jammer and the size of the denial area is determined by the transmitter power and altitude. (GPS signals are very weak and it doesn't take much power to jam a significant area.)

Doug

 

[bikehikeskifish]

It is also centered over Florida so it would appear to be unlikely to bother the majority of the readership in the New England/New York area.

Still, testing will continue through 2/22? Come on guys, isn't that a little bit long?

Tim

 

[Kevin Rooney]

It is also centered over Florida so it would appear to be unlikely to bother the majority of the readership in the New England/New York area.

Am wondering if/how it impacts air travel?

Am I agree - the impact on the VFTT hikers who only hike on the east coast is minimal. I posted the information because I didn't realize that these tests occurred, and found it of interest. I think others will as well.

 

[DougPaul]

Am wondering if/how it impacts air travel?

It might affect some. However scheduled passenger jets have other methods of navigation which can be used during a GPS outage.

Am I agree - the impact on the VFTT hikers who only hike on the east coast is minimal. I posted the information because I didn't realize that these tests occurred, and found it of interest. I think others will as well.

Some may remember Selective Availability--the intentional degrading of civilian GPS to an accuracy of ~100 meters. Its purpose was to deny enemy users weapons targeting level accuracy. Once theater (local zone) jamming was proven, it was no longer necessary. (It was turned off in 2000 by presidential order. It will never be turned on again.)

Remember, GPS was initially conceived as a military navigation system. It now, by law, serves both military and civilian purposes.

Doug

 

[bikehikeskifish]

Some may remember Selective Availability--the intentional degrading of civilian GPS to an accuracy of ~100 meters. Its purpose was to deny enemy users weapons targeting level accuracy. Once theater (local zone) jamming was proven, it was no longer necessary. (It was turned off in 2000 by presidential order. It will never be turned on again.)

I do - it was less accurate than Loran. Then came dGPS to make up for the errors. When you spend hundreds of $ on fuel and take a day off shore, it is painful not to be able to find your spots.

Am I agree - the impact on the VFTT hikers who only hike on the east coast is minimal. I posted the information because I didn't realize that these tests occurred, and found it of interest. I think others will as well.

When I first read the post (not the article) it wasn't immediately obvious that the impact to the northeast was minimal, if not non-existent. If you are only scanning this post, you may walk away with the impression that east coast = northeast and that northeast service will be interrupted.

Tim

 

[Remix]

I am amazed that no one is complaining given that GPS is used for e911 cell calls, distress beacons, vessel traffic control, precision aircraft approaches, utility and communication systems synchronization, etc etc etc.

 

[Kevin Rooney]

I am amazed that no one is complaining given that GPS is used for e911 cell calls, distress beacons, vessel traffic control, precision aircraft approaches, utility and communication systems synchronization, etc etc etc.

Am not sure people know about these outages. Our level, at least in the US, of general news coverage has shrunk enormously in the past 10 years.

 

[DougPaul]

I am amazed that no one is complaining given that GPS is used for e911 cell calls, distress beacons, vessel traffic control, precision aircraft approaches, utility and communication systems synchronization, etc etc etc.

Not to mention that the US, in its infinite (IMO lack of) wisdom, shut down the only viable backup (Loran and its extension eLoran which has accuracies similar to civilian GPS)...

I suspect that any serious complaints would be met with the "national security trumps all" defense.

Doug

 

[DougPaul]

Am not sure people know about these outages. Our level, at least in the US, of general news coverage has shrunk enormously in the past 10 years.

Notice is given in such places as NOTAMs (http://en.wikipedia.org/wiki/NOTAM). People who are critically dependent on GPS should check such sources before going out.

I suspect that most non-professional GPS (and perhaps some professional users) users are unaware of such sources.

Doug

 

[Remix]

Well there was a newsgroup called alt.risks. Years ago, several posters reported that the military was cutting off GPS--but only around missile ranges and such.

Are ATT and Verizon letting their customers know that the police wont be able to find them in any emergency. (as quickly).