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Ionospheric Interference With GPS Signals

Posted by kdawson on from the trusting-your-garmin dept.

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.

17 of 127 comments (clear)

  1. Time to declare war? by Anonymous Coward · · Score: 5, Funny

    The electrons in the ionosphere must be terrorists!

  2. Oblig. by elguillelmo · · Score: 3, Funny

    Tinfoil hats ahoy!

    --
    Dawkins Revisited: A person is shit's way of making more shit -- Steve Barnett, anthropologist.
  3. Dual Frequency by Detritus · · Score: 4, Interesting

    I thought that was why the military version of GPS used two frequencies. From what I've read, it allows them to measure the actual propagation delay through the ionosphere, instead of relying on the static delay prediction model used in the single frequency mode used by civilians and those without a crypto-keyed military GPS receiver.

    --
    Mea navis aericumbens anguillis abundat
    1. Re:Dual Frequency by jrumney · · Score: 3, Informative

      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.

    2. Re:Dual Frequency by DRobson · · Score: 3, Interesting
      Yeah, it appears so. In order for the random error to be useful for non-military use the error had to be somewhat uniform across large regions. So, once you established the error on one known point you were pretty right.

      Also, it looks like military personnel ended up buying there own civilian units a large percentage of the time with obvious problems.

      Looks like it was officially disabled around 2000 or so.

    3. Re:Dual Frequency by The+Evil+Couch · · Score: 4, Interesting

      I don't think scarcity was driving the conversion that much; I found PLGRs pretty common in the Army while I was in (1998-2005). However, the main draw to commercial GPS products was that the PLGR had a fucking awful UI and was about the size of a hardbound dictionary. The internal hardware and screen was hopelessly out of date by the time it was in common usage. Entering numbers by pressing UP/DOWN? No visual map? A control scheme that required a knowledgeable or at least technologically apt soldier to? Fuck that! If there's a navigation tool for my squad, I need everyone in the squad to be able to use it. If I'm the only one that can make use of it and I go down, it's instantly become useless.

      That's not to say that it was a total piece of shit. It was water-proof and pretty durable. It was really extensible; it could be plugged into a variety of other things, which made them really useful *if* you had the proper hardware. The problem was that all the needed gear to take full advantage of it required a vehicle to transport and provide power. The PLGR was a fantastic piece of gear for anyone but the infantry. Problem is, there's a hell of a lot more infantry that needs coordination on the ground than there is anyone else. So, many of us bought our own.

      --
      The World's Worst Webcomic!
  4. Good Grief! by Anonymous Coward · · Score: 4, Interesting

    More Roland fest! Why doesn't SourceForge just hire the guy? Good grief! Who's he giving blow jobs to?

    1. Re:Good Grief! by jacquesm · · Score: 4, Interesting

      why is his stuff getting this insane posting ratio on ./ ? Since march 21st of this year 20+ accepted submissions ??

      --
      MP3 Search Engine
    2. Re:Good Grief! by Frosty+Piss · · Score: 4, Funny

      I for one welcome our new Roland Overlord. May he pour hit grits down Natalie Portman's shorts, I'll take a Beowulf cluster of that! I'll bet in Soviet Russia they can't even get Roland. But one thing is for sure, he does run Linux. And all these stories of his on Slashdot almost certainly result in Profit!

      --
      If you want news from today, you have to come back tomorrow.
    3. Re:Good Grief! by owlnation · · Score: 5, Interesting

      Agreed. Slashdot editors take note: a lot of people here do not think Roland is neither intelligent enough nor qualified to be making /. at all, but 20+ articles in a few months is a total disgrace. There are many people here who absolutely hate this guy and the off-the-wall, irrelevant, discovery-channel-level science, garbage he writes. Showing bias towards him is going to hurt you long term, it's already losing you respect.

    4. Re:Good Grief! by jacquesm · · Score: 4, Interesting

      Let me spell it out for you, I'll ignore your strawman about me not liking him 'because he's french', I don't know what prompted you to say that, it lowers the discussion level:

      Roland has an extremely high ratio of postings and a *much* higher ratio of accepted postings. So much higher that for the longest time I figured he was a sockpuppet for one of the ./ editors. Once you start noticing and analyze the quantities of stories getting rejected from other members, the quality of those stories and how many of Rolands stories get accepted and the quality of *those* stories then you really can't help but wonder what the game is here.

      The discrepancy is too large to be ignored or brushed under the carpet.

      After all, the ./ firehose gives you a pretty good idea of which stories make the grade and which don't (besides of course a guaranteed placement of dupes ;) ), and it allows you to get a good idea of the average submission quality of stories that eventually don't make it.

      The standards that most postings are held to would mean that *none* of Rolands postings would have been accepted, they are the very definition of blog spam.

      Something is smelly here, even if I can't quite put my finger on it. Maybe it's time to do some scripting to get some real hard stats on this whole thing.

      --
      MP3 Search Engine
  5. Re:GPS is digital! by canavan · · Score: 3, Insightful

    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.

  6. Re:GPS is digital! by borizz · · Score: 4, Interesting

    Thats not how GPS works however. The satellites hum a digital tune. The receiver hums the same tune. It then measures how much later the sat's tune is heard. With this and the speed of light you can calculate how far the satellite is from you. Get distances to three sats and you can triangulate your position.

    So you might hear the tune fine, but if the ionosphere delays the tune every so slightly, your reading will be off and your position will be inaccurate.

  7. Re:GPS is digital! by spandex_panda · · Score: 5, Informative
    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!

    --
    like phosphorescent desert buttons singing one familiar song
  8. However, if you're a Ham.... by caluml · · Score: 4, Interesting

    However, amateur radio people such as myself rub their hands with glee, as a reflective ionosphere means good DX :)
    I check the "Space dials" regularly, and can't wait for them to be in the red! 73s.

    --
    Get your own free personal location tracker
  9. No Problems for me... by Frightened_Turtle · · Score: 3, Insightful

    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!
  10. Hence WAAS by RJFerret · · Score: 3, Insightful

    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