Ionospheric Interference With GPS Signals

Roland Piquepaille writes "In recent years, we have become increasingly dependent on applications using the Global Positioning System, such as railway control, highway traffic management, emergency response, and commercial aviation. But the American Geophysical Union warns us that we can't always trust our GPS gadgets because 'electrical activity in the... ionosphere can tamper with signals from GPS satellites.' However, new research studies are under way and 'may lead to regional predictions of reduced GPS reliability and accuracy.'" Roland's blog has useful links and a summary of a free introduction, up at the AGU site, to a special edition of the journal Space Weather with seven articles (not free) regarding ionospheric effects on GPS.

Comments

Re:GPS is digital!

[spandex_panda]

Actually this is not true. The digital code modulated onto the radio waves is affected by the ionosphere too. The military gets 2 'code' signals on 2 frequencies, but geodetic or surveying GPS gear observes the 'phase' of the frequencies, there are L1 and L2 frequencies which are observable and you can combine them to cancel out the ionospheric effects. Observing everything, civilian code, carrier frequencies, military P codes, can give you a single point precision of a couple of cm in horizontal (an inch for you yanks) and something like 3 times that in vertical.

Just receiving a digital signal doesn't mean its right!

Re:Dual Frequency

[jrumney]

I thought they'd stopped injecting error as a routine measure a few years back. It is so easy to get around that I doubt it serves any military purpose, even for relatively unsophisticated enemies.