U.s. Conducting Massive Gps Jamming Tests

[+Redwoods Mtn Biker]

Check out the map (and story) I just posted on GPS jamming tests. Somebody please tell me I'm misinterpreting.

 

Rich Owings

www.MakeYourOwnMaps.com

www.GPStracklog.com

 

“We were desert mystics, my friends and I, poring over our maps as others do their holy books.” – Edward Abbey

[+embra]

Huh. Looks like it's been going on for awhile already. Any Californiers noticed an impact on the designated days?

[nda1977]

When I worked for the DoD, some of the military contingent indicated that they made tests for this all of the time, both to challenge our ability to make false signals and test how opposing forces can disrupt signals in localized settings. But I'd always gathered that efforts were on a very, very focuses scale. While I cannot gauge this into useful distances, it does seem suspect that the tests would extend beyond the China Lake testing range, simply because of the dependance upon GPS & WAAS by the FAA. While I can understand jamming over restricted airspace, it seems improbable that this would affect airspace beyond the China Lake.

 

I may very well be wrong, but this just sounds a little dubious to me.

[+Redwoods Mtn Biker]

Yeah, I question it myself, but if you look closesly at what they are saying, the signal WILL be unreliable in a 230 nautical mile radius at 4,000' elevation, and the effect decreases with altitude. So it is improbable that there is an impact on commercial flights. Perhaps there is no impact at ground level either?

 

Rich Owings

www.MakeYourOwnMaps.com

www.GPStracklog.com

 

“We were desert mystics, my friends and I, poring over our maps as others do their holy books.” – Edward Abbey

[nda1977]

Yeah, I question it myself, but if you look closesly at what they are saying, the signal WILL be unreliable in a 230 nautical mile radius at 4,000' elevation, and the effect decreases with altitude. So it is improbable that there is an impact on commercial flights. Perhaps there is no impact at ground level either?

...

 

Good point. For the effects at altitude, I think that it would be a matter as to how much degredation is encountered. If the degredation decreases to nil at ground level, though, then I would imagine that it would have very little impact on ground-based GPSr's. Further, perhaps, the huge radii listed could be a far-fetched extreme of effect. When I participated in wargames, the notices concerning jamming (rf) was always well beyond the range of operations and well beyond the limitations of the jamming instruments. It could be that the Coast Gaurd has expanded the radius of effect two or three times the actual affected areas. And it also depends on the connotation of "jamming" (i.e., whether or not they're truly jamming the signals or just spoofing the signals).

 

But it all seems moot until someone takes a GPSr out into the backcountry and tells us that the GPSr was way off of the mark, or a pilot says that they're GPSr was well out of sync with DME readings or positions estimated from VOR/NDB stations.

[peter]

Yeah, I question it myself, but if you look closesly at what they are saying, the signal WILL be unreliable in a 230 nautical mile radius at 4,000' elevation, and the effect decreases with altitude. So it is improbable that there is an impact on commercial flights. Perhaps there is no impact at ground level either?

 

Not quite. It indicates that the maximum radius is 230 nm at an altitude of 40,000' (FL400), 175 nm at an altitude of 25,000', and only 120 nm at an altitude of 4000' above ground level. So despite the implication of decreasing radius with altitude, the actual numbers given show that the affected radius increases with altitude, at least from around 4000' to 40,000'.

 

Commercial flights are not yet dependent on GPS and they would be well aware of the times when these tests could be in effect. WAAS and RAIM should also be effective in notifying the pilot if the signals are giving untrustworthy data.

 

And it appears that the testing may be done in such a way that effects near ground level are reasonably localized although it would be nice if that were explicitly stated (120 nm still covers a very large radius and it's not clear how much smaller it might be at ground level rather than 4000' above).

 

I agree with nda1977 that the notice is likely to err on the conservative side. I.e. specifying a much larger area than is actually expected to be affected.

Edited February 5, 2006 by peter

[+Redwoods Mtn Biker]

Not quite. It indicates that the maximum radius is 230 nm at an altitude of 40,000' (FL400), 175 nm at an altitude of 25,000', and only 120 nm at an altitude of 4000' above ground level. So despite the implication of decreasing radius with altitude, the actual numbers given show that the affected radius increases with altitude, at least from around 4000' to 40,000'.

My error. Thanks for catching it.

 

Rich Owings

www.MakeYourOwnMaps.com

www.GPStracklog.com

 

“We were desert mystics, my friends and I, poring over our maps as others do their holy books.” – Edward Abbey

[+GPS Guy]

HERE is a link to The FAA's NOTAMS for select areas. Click on the button for "All GPS NOTAMS". It verifies the lack of good GPS signals over Tonapah.

 

I would suspect a ground based "jammer" at the location due to the fact the effect is at a shorter range at lower altitude.

Edited February 5, 2006 by Marc G.