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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.
The data encoded in the signal is digital, however, the location information is derived from the timing of the signal, something that changes depending on the medium (i.e. the distance within the atmosphere the signal has to travel and the precise compisition and electrical conditions therein). I thought that ionospheric corrections were something that was part of the WAAS standard, or at least something that tended to be corrected by using WAAS. The wikipedia article lists this as part of "slow" corrections.
Doesn't cause any problems for me. Sometimes I've got just a few feet of accuracy in my position, other times it's 10's of feet. I guess it would cause issues with my home-made cruise missle, though...
Aviation has used VOR navigation for decades, developed during WWII. And the US Government has a big OFF switch for that, too. Part of pilot training is knowing how to navigate when all the fancy gadgets are offline. Because you never know when a system will fail.
I just view this as a confirmation of what I've noticed before: that sometimes the signals aren't as good as others. Fortunately, I have a computer that is capable of recognizing the situation and performing the necessary error correction on the fly. I call it my brain.
Whew! This water sure is cold!
I've used GPS receivers since 2001 almost daily (I was even featured on CBS news geocaching). A LOT has changed in that time, but WAAS is a brilliant feature all GPSrs now incorporate, that totally adjusts for ionospheric disturbances, by broadcasting corrections from ground stations.
In geocaching, the greater the accuracy the better. For car navigation, you don't even need it, as the accuracy is better than the width of a road regardless!
This article seems to be a decade behind... -Randy