Follow Slashdot blog updates by subscribing to our blog RSS feed


Forgot your password?
United States Technology

U.S. May Reduce Non-Military GPS Accuracy 772

ward99 writes "The U.S. government may be degrading GPS satellite signals, to cripple Iraqi forces' ability to use those systems during the war. This could potentially reduce accuracy from ~3 meters to over ~100 meters. Users depending on GPS systems may want to do sanity checks on any data returned by those systems during the war. The U.S. will do this by increasing the inaccuracies on the civilian C/A code, turning back on S/A (Selective Availability), by having the satellites deliberately and randomly return inaccurate information on where they are. S/A degrades GPS accuracy to only 100 meters 95 percent of the time and 300 meters the other 5 percent of the time. This will not effect the military P code."
This discussion has been archived. No new comments can be posted.

U.S. May Reduce Non-Military GPS Accuracy

Comments Filter:
  • shouldn't have scratched our own satelite project (named Galileo, IIRC)
    • by pteron ( 11383 ) on Wednesday March 19, 2003 @07:48AM (#5543082)
      According to ileo/faq/index_en.htm
      it hasn't been scratched.
    • Well, there's always GLONASS [].

      [sigh] Poor Russian space program.

    • shouldn't have scratched our own satelite project (named Galileo, IIRC

      I am from Europe myself but I am not sure I agree. The reason Galileo is not going anywhere quick is that is enormously expensive (just as GPS was).

      Is it really worth the money and the effort to send up an entire system so that coverage can be ensured during the say 2% of time when the GPS signals are distorted for military reasons? I can see a any number of scientific/ infrastructure projects that are much more worthwhile. Of cour
    • This was *exactly* why we here in Europe shouldn't have scratched our own satelite project (named Galileo, IIRC)
      I would have a hard time seeing the EU not including exactly the same capability in Galileo, since control of precision targeting capability is critical for national defense. Of course, perhaps the EU is anticipating that it will have no concept of national defense by the time Galileo arrives.


    • havn't scratched our own project (Galileo). The first of the 30 satellites (27 + 3 active spares) will be launched in 2004, with an initial service operational by 2006 and the full system operational by 2008. The links are here [] (European Commission site), and here [] ESA site).

      I think you must have been mistaken - IIRC the US tried to persuade Europe to dump the project, basically because it will be accurate to around 45cm (guaranteed to withing 100cm), whereas GPS can often be several dozen metres out (and h
  • Army's stuff (Score:5, Insightful)

    by SlamMan ( 221834 ) <squigit AT gmail DOT com> on Wednesday March 19, 2003 @07:41AM (#5543052)
    Don't like it, but it's the army's stuff. They can degrade it that far if they want to. Don't like it? Send up your own GPS satalites.
    • Re:Army's stuff (Score:3, Interesting)

      by Gordonjcp ( 186804 )
      Or use differential GPS, and get accuracy to a few tens of millimeters.
      • Re:Army's stuff (Score:4, Informative)

        by Apro+im ( 241275 ) on Wednesday March 19, 2003 @08:03AM (#5543151) Homepage
        Actually, won't work - differential GPS only really corrects the innacuracies inherent to the correctly operating system.

        IIRC, differential GPS is where you correct for clock error by using a fixed point with a very accurate latitude/longitude measurement as one of your "sattelites". However, let's say the GPS sattelites decide to coordinatedly broadcast the signal that according to the receiver's internal database hey would a few nanoseconds in the future - it would throw off all correction measures, since they all depend on all your sattelites (including your ground station "sattelite") to be using the same clock, and that that clock matches up with the database.
        • Re:Army's stuff (Score:5, Informative)

          by stienman ( 51024 ) <.adavis. .at.> on Wednesday March 19, 2003 @01:26PM (#5545065) Homepage Journal
          This is incorrect. A DGPS transmitter knows its own location, and can therefore determine the error of each satellite in its view.

          It then sends a DGPS stream out, and any GPS receiver capable of receiving that stream can remove the satellite error for satellites they share with the DGPS transmitter.

          However, typical low end DGPS will only reduce the error (when SA is turned ON) to 10 meters or so. The receivers used by surveyers with DGPS can go to the centimeter level, longitudinally and latitudinally. Altitude is a different matter...

          Garmin is using a system similar to DGPS called WAAS which also helps reduce the error.

          The encoded GPS signal the military uses along with high end receivers will, IIRC, go down to the meter without any DGPS. The reason they can't get any better than to the meter is that the atmospheric effects on the signal can't easily be corrected for in real time.

          A decent tutorial can be found here []

    • Like Galileo? (Score:5, Insightful)

      by gotan ( 60103 ) on Wednesday March 19, 2003 @08:42AM (#5543295) Homepage
      Well, it seems the US government isn't too comfortable [] with that and tries (german link) [] to make (german link) [] the EU abandon that project. Naturally the EU doesn't like [] depending on a US-monopoly for such an important system.

      • Rumor has it... (Score:3, Interesting)

        by Andy Dodd ( 701 )
        that the US turned off SA in the first place to neuter the Galileo project by reducing its perceived need.

        Well, the second time the US turned SA off was for that reason.

        This article is really amusing because of the fact that the government actually turned SA OFF for the last Gulf War, as there was a shortage of military GPS receivers and soldiers were ordering civilian units mail-order.
        • Re:Rumor has it... (Score:3, Informative)

          by UberLame ( 249268 )
          The Wall Street Journal was recently reporting that many soldiers are feeling over weighted with stuff to carry, so they are resorting to chucking all MRE items that aren't particularly high in carbs, and tossing the GI GPS units for civilian ones that use the same batteries as their headsets to reduce the different types of batteries that must be carried in the field. I'd imagine that such soldiers would be rather disappointed if they had to go back. According to the article, the Army is aware that this
    • Re:Army's stuff (Score:5, Informative)

      by moon_monkey ( 323491 ) <> on Wednesday March 19, 2003 @09:43AM (#5543565)
      Well, you can believe what some German automobile club says, or you can talk to the Pentagon - According to the story on New Scientst [] they've promised not to degrade the signal. "We would not create a global problem for transport out of spite for Saddam," says a spokesman at the US Department of Defence.
  • by James_Duncan8181 ( 588316 ) on Wednesday March 19, 2003 @07:42AM (#5543055) Homepage
    As the GPS network can be degraded or upgraded region by region. I used to be in military service and one of our tips for civilians was that they could always tell when the shit was really about to hit the fan because the GPS accuracy will change massively when compared to a know coordinate point.

    Interestingly we were also told that it is not usually done before 24h from action. Anyone want to go a $10 bet with me on that? ;)

    • I was going to say that I thought they had figure out how to scramble or turn on SA where they wanted to. Do the editors check even the story? The newsline was frankfurt, not here in the good old US of A! The old SA is not going to be reinstated. Too many of our homeland thing depend on it. Planes, delivery persons and anyone else who needs to know where they are. Things are much different then during the gulf war. Many people depend on GPS's for at least some navigation.
      • GPS and boating. (Score:5, Informative)

        by fmaxwell ( 249001 ) on Wednesday March 19, 2003 @09:48AM (#5543601) Homepage Journal
        Things are much different then during the gulf war. Many people depend on GPS's for at least some navigation.

        You are absolutely correct. I am a boater and GPS enabled me to find channels and return to port late at night after effecting repairs at sea and after being forced to return to port at slow speeds due to rough seas. GPS is important enough to me that I always have two units on my boat, a console-mounted unit and a handheld which I keep for backup in case the console unit fails. Most boaters now rely on GPS extensively and, while 100 meter accuracy on the open seas is often acceptable, it would cause havoc on inland lakes and waterways as well as at coastal ports.

        I know that this may sound melodramatic, but turning S/A back on will result in deaths and injuries. I'm not saying that death or injury would be common, but it would happen, whether because someone hit an obstruction or because they ran aground in inclement weather. While many smarmy, self-impressed types will, no doubt, claim that these people relied on GPS too heavily, don't listen to them. These are probably the same people who would freak if their depth finder went out, couldn't fix their engine if it failed, and think that a sextant is a marital aid. Marine radar, sonar depth finders, VHF radios, and accurate GPS have all increased safety on the water. Take any of them away, and deaths and injuries will go up.
      • by Reinout ( 4282 ) <> on Wednesday March 19, 2003 @10:16AM (#5543772) Homepage
        Civilian GPS in gulf war 1 []

        Look at the second paragraph from the bottom. They were about to reduce the usability of civilian GPS systems during the first gulf war. Turned out that many military personell was carrying their own, civilian, equipment. It wasn't standard issue back then yet.

        So they left the resolution cranked up to max, their own soldiers would be most hampered by a downgrade...

      • by Andy Dodd ( 701 ) <{atd7} {at} {}> on Wednesday March 19, 2003 @11:08AM (#5544096) Homepage
        News for you buddy: The government can and will turn SA back on any time they want to. It's always been clear that this is the case and anyone who relies on SA being turned off for a critical application is just plain stupid and they deserve what they get if it's turned back on.

        Do you think that in less than three years people have forgotten about SA? Yes, that's right, SA was only turned off on May 1, 2000 - It hasn't even been three years.

        Not a single plane in commercial use today was designed after the SA turnoff - No one designs a commercial jetliner in under 3 years. Every plane that uses GPS has been designed with the assumption that SA can be turned back on any time. In fact, they're designed with many other backup navigation systems, GPS is just a nice convenience but it's the system LEAST relied upon by airplanes.

        Delivery people? 100 meters is good enough for these people. At least it had better be - Anyone relying on their GPS rather than having their eyes on the road should have their license revoked immediately. I don't need a UPS driver rear-ending me because he was staring at his GPS.

        Face it, 100 meters is more than good enough for most people. For those who need "some navigation", 100 meters is good enough. For those who need more precision - They had better not be relying on SA being off, if they are they're dumb.

        Note that survey-grade receivers can achieve millimeter accuracy even with SA turned on. (Thanks to reference stations with known locations that produce data which can be used to measure SA errors and correct for them in postprocessing, among other expensive tricks.)

        If the military things turning on SA is a good idea and will help them in the war, SA will be turned on. (Note: There IS a chance that the military could decide that leaving SA off is a good idea, but civilian needs will not factor into the decision at all. During the first Gulf War, military-grade GPS receivers were in short supply and many soldiers phoned home to order civilian units. Military receivers were also unusually large at that time. As a result of this short supply, SA was actually turned OFF for the last Gulf War. Chances are that a lack of military-grade receivers is NOT an issue this time around, and dual-frequency receivers are a fraction of the size they used to be.)
    • As the GPS network can be degraded or upgraded region by region.

      It's OK, I've got the multi-region hack for my GPS decoder ...


  • by pork_spies ( 659663 ) on Wednesday March 19, 2003 @07:43AM (#5543062)
    Would be interesting to know what the EU would do with Gallileo at this moment in time. I dare say they would follow the US lead, I suppose...
  • by kEnder242 ( 262421 ) on Wednesday March 19, 2003 @07:45AM (#5543070)
    Last time they turned off the S/A during the war, cheaper that way using off the shelf gps.

    You can always have a radio broadcasting the offsets from a known location to compensate.
    • by Nogami_Saeko ( 466595 ) on Wednesday March 19, 2003 @07:54AM (#5543110)
      There was a big discussion on one of the GPS newsgroups about this very fact - at the time of the last gulf war, civillian GPS units were cheaper, more plentiful, and had more features that the troops wanted/required than the more cumbersome military GPS units.

      One of the soldiers was talking about it in the group and basically said the military units were limited to showing long/lat and doing goto-waypoint distance/direction operations. At the same time, civillian units had mapping capabilities, easy to use graphic displays, and were about 1/2 the size.

      As other posters have said, it's possible to adjust the SA signal geographically, so they could degrade the signal in the middle east without changing anything in north america. This is the first step that seems logical.

      Alternately, they could leave SA off alltogether, and just jam the GPS signal in the area that they are performing operations - the GPS signal is relatively weak and an ECM aircraft could easily block hundreds of miles of GPS reception while flying out of range of ground-based weaponry.

  • by guybarr ( 447727 ) on Wednesday March 19, 2003 @07:45AM (#5543072)

    My guess is that for high-precision locations, the Iraqis already measured them with high accuracy, while for, say, infantry navigation all you really need is 100m accuracy. (Even less for armored forces, of cource)

    And given the air threat, I also doubt their forces will change their localtions too much; if it's camouflaged enough to survive the initial attacks, it will probably stay put.
    • My guess is that for high-precision locations, the Iraqis already measured them with high accuracy, while for, say, infantry navigation all you really need is 100m accuracy. (Even less for armored forces, of cource)

      That's an awfully big assumption. Consider the terrain in southern Iraq. A few tens of metres (or less) is the difference between fording a river with your tank, and getting bogged down in marshland and having to sit and wait for a recovery vehicle, and all the while vulnerable to air attack. I
  • by Anonymous Coward on Wednesday March 19, 2003 @07:46AM (#5543074)
    Do they really know how much a captain depends on GPS these days, especially when it comes to passing in and out of harbors? I hope this won't wreck another tanker somewhere.
  • by MyNameIsFred ( 543994 ) on Wednesday March 19, 2003 @07:46AM (#5543076)
    Let me understand this, the head of a German Autoclub says the U.S. military MAY, I repeat MAY, degrade GPS accuracy. No evidence. Just pure conjecture. Consider that GPS has woven itself into our lives. How, it arguably supports critical functions. I strongly doubt that they will do this. While I understand the world's fears concerning GPS because it is run by the military, I put this article in with all FUD.
  • What about planes?? (Score:5, Interesting)

    by borgdows ( 599861 ) on Wednesday March 19, 2003 @07:46AM (#5543077)
    Civilian planes use GPS, don't they?
    What about other critical systems like police, ambulance, fire brigades and so on??
    • by mwillems ( 266506 ) on Wednesday March 19, 2003 @08:04AM (#5543154) Homepage
      In small planes (I used to fly them), GPS is auxiliary. A good pilot does not rely on GPS. Precisely becuase it dould be disabled.

      And in large aircraft, where GPS is used there are many other systems as backup. And final approach etc is of course never based on GPS. So, do not worry.

    • by flonker ( 526111 ) on Wednesday March 19, 2003 @08:06AM (#5543163)
      Last I heard, GPS is not approved for navigational use by the FAA. Meaning, you can use it, but you need to have alternate systems, and can't rely on it.

      Civilian planes will still use navigational radio beacons. This is one of the first things they teach you when you go for a private pilot's license. (First step for a non-military commercial pilot's license. Military licensing is probably similar.)
      • by FreeUser ( 11483 ) on Wednesday March 19, 2003 @09:26AM (#5543455)
        Last I heard, GPS is not approved for navigational use by the FAA. Meaning, you can use it, but you need to have alternate systems, and can't rely on it.

        Your information is a little dated. GPS is most definitely approved for navigational use. Indeed, many NDB approaches have already been replaced with GPS approaches, and new GPS approaches are being certified all the time.

        My aircraft has a Garmin 540 GPS Nav/Com installed, which is certified for instrument approaches. All that having been said, as another noted, any competent pilot knows how to fly using a number of instruments, with as much redundancy as possible. Dialing in VOR (a radio navigational aid) and using DME (distance measuring equipment), monitoring a moving map GPS, and even having a VFR-only LORAN all dialed up and operational at the same time provides invaluable cross-checking, should one instrument or another fail.

        I've had my DME fail (but had GPS and even the LORAN availabe as a cross reference, in addition to triangulating two separate VORs), I've had my DG fail (but had the compass and, again, the GPS to cross-check with), and once I even had my compass fail (a seal went bad and the kerosine leaked out, so, while the compass still worked, it was far too wobbly in any but the smoothest conditions to be of much use). Once again, the GPS and working DG were sufficient to navigate on to the next decent sized airport, where I got it fixed. As for my NDB ... I had the finicky thing pulled out to make room for my GPS Nav/Com ... an additional glide slope, moving map positional awareness, and nav/com more than made up for the loss of AM Radio reception and the ability to navigate using an ever decreasing number of NDB stations. Of course, in South Dakota a number of AWOS and ASOS stations broadcast on NDB frequencies, but then that is what UNICOM or Flight Service are good for, in a pinch.

        Pilotage (using visual references like lakes, landmarks, etc.), radio navigation, and competency with a GPS are all skills that are taught a civilian pilot (assuming said equipment is available). For an instrument rating, if the instrument is in the panel, you will be tested on it. This definitely includes a moving map GPS, if your aircraft is equipped with one, and flying a GPS approach if it is IFR certified.
  • There are plans for building a similar system to GPS in Europe so that we are not too much depending on the american empire. The following page [] nicely explains the concept. More is available here []. This is technically very interesting and should open up new possibilities for navigation. Furthermore being constructed jointly by many partners and nations we can be reasonably sure that it can not be compromised by one weak leader.
  • by Noryungi ( 70322 ) on Wednesday March 19, 2003 @07:50AM (#5543094) Homepage Journal

    John R. Smith, of Peoria (Ill.) drove his brand-new SUV through the security glass doors of his bank, while following his GPS navigator.

    "I was only following the indications of this @!!%!! machine -- and it told me I still needed to travel straight ahead for a hundred meters!", Smith tried to explain as he was taken into custody by the Peoria Police Department for "breaking and entering".

    The Peoria Intercontinental Bank representatives were unavailable for comments.

    • by j7953 ( 457666 ) on Wednesday March 19, 2003 @09:15AM (#5543412)

      This did actually happen in Germany: some idiot drove his car into a river because the navigation system displayed a bridge, but actually there was only a ferry.

      See pictures of his car here [] (scroll down).

      The last paragraph of the text says: "Please note: A GPS system cannot be a substitute for the driver's attention! In december 1998, a driver trusted his navigation system which suggested to continue driving straight ahead. A few seconds later, his car got wet because his road database didn't know anything about the ferry across the Havel (a river near Berlin). This is not a joke! The TV channel RTL had a report."

  • STDMA (Score:3, Interesting)

    by G3ckoG33k ( 647276 ) on Wednesday March 19, 2003 @07:51AM (#5543099)
    There is a better alternative to GPS named STDMA (Self-organizing Time Division Multiple Access). It is patented with U.S. Patent No. 5,506,587, which you may find HERE [].

    It is in use in marine navigation. See also HERE [] and for a tech overview HERE [].

    Apparently, the US has tried to suppress the system as it may well replace GPS because of better performance and other reasons; one can imagine wartime control may be of importance here.
  • by avdi ( 66548 ) on Wednesday March 19, 2003 @07:52AM (#5543103) Homepage
    It's more likely that localized blackout or jamming in the Iraq region will be used, rather than a global downgrade. See here [] for more.
  • by Gryftir ( 161058 ) on Wednesday March 19, 2003 @08:05AM (#5543161) Homepage
    There are two alternatives to the GPS system.

    Galileo, which is planned to be completed in 2008, is the EU's alternative. It uses dual frequencies, and may increase accuracy to only a meter. Unforunatly, not all of the 30 sattelites are deployed, and the recievers don't seem to have been built.


    GLobal Orbiting NAvigation Satellite System

    this is the Russian system, which has a 10 / 20 meter accuracy for it's military signals, and 100 meter accuracy for it's degraded civilian signals.

    If Iraqi is going to use something else, it would probably be GLONASS as it is fully operational.

    • A few civil engineers I know who do some survey work use big, expensive receivers that pick up both GPS and GLONASS signals to further increase accuracy. Why aren't there any consumer-level units that pick up both GPS and GLONASS signals? The more satellites you get, the better your fix, and if the unit was smart enough to notice SA being turned on, it could use the GLONASS fix instead.

      I'm assuming that somewhere there are cheap civilian GLONASS receivers-- if they cost about the same as cheap 12-channel
  • by SecGreen ( 577669 ) on Wednesday March 19, 2003 @08:09AM (#5543178)
    Click here [] for the AFSC's GPS Constellation Status Page. Assuming that it isn't deemed operationally sensitive info, any announcement of reduced capability should be available here.
  • Alternatives (Score:5, Insightful)

    by Bozovision ( 107228 ) on Wednesday March 19, 2003 @08:19AM (#5543225) Homepage
    And this is EXACTLY why the EU wants their own alternative civilian version of GPS [], and why the US has argued against it []. Suprise!

    Apparently the Pentagon sees no compelling reason [] for an alternative to GPS. Oops, that would be before they checked their GPS units round about now. Oh wait, I forgot, they have their fingers on the buttons, perhaps that why they can't see a compelling reason.

    Oops look; those pesky photons might interfere with each other []

    On the other hand, to be fair, the US could have just degraded the signal without announcing it. At least now ships and planes probably won't be piloted into rocks.

    • Re:Alternatives (Score:3, Interesting)

      by Moridineas ( 213502 )
      THanks for the links. Very informative. In their it says that the US military has never degraded civilian service, neither during Gulf War I or during Kosovo. Though there are contigency plans to limit affectiveness for a specific area (from one of the links). Sounds good to me. But the important part is that it's never been done.

      The interference sounds like a very serious issue as well.

      Also, the US didn't annoucne anything--we still have no idea if the signals will be degraded or not. This all come
  • onstar? (Score:5, Funny)

    by Joe the Lesser ( 533425 ) on Wednesday March 19, 2003 @08:27AM (#5543256) Homepage Journal
    Don't a number of commercial services like onstar use gps to track vehicles?

    'Be calm madam, you are not lost. According to us you are floating off the coast of San Diego. You should be fine once high tide rolls in.'
    • Re:onstar? (Score:5, Funny)

      by Lxy ( 80823 ) on Wednesday March 19, 2003 @11:14AM (#5544140) Journal
      I've got a friend in MN. One winter night he and his buddies decided to have some fun with Onstar. Knowing that the call center is somewhere in Florida or California, they drove onto Mille Lacs lake (a very huge lake for those of you who don't know, it's larger than most counties). They called up Onstar to ask for directions:

      Onstar: "hello?"

      Friend: "We're lost. Can you help us find our way back?"

      O: "Sure, hold on. Hmm.. this must not be working right. It says you're in the middle of a lake!"

      F: "I know. We need to find our way back to shore"

      O: "????"

      F: "We're in Minnesota. There's ice on our lakes here"

      O: "???? How are you in the middle of a lake?"

      F: "We drove out on the ice"

      O: "Why would you do that?"

      F: "Ice fishing"

      O: "?????"

      F: "Can you direct us to the nearest landing?"

      O: "Umm.. hang on a second. I need to get my supervisor."
  • by Drunken_Jackass ( 325938 ) on Wednesday March 19, 2003 @08:29AM (#5543257) Homepage
    S/A has always been a bit of a farce. It can be circumnavigated (no pun intended) if you use Differential GPS.

    Basically, you set one GPS receiver up at a known, surveyed location and program that location into the unit. Then when the receiver trilaterates its position based on the information the satellites provide, it does on-the-fly corrections (You say i'm here, but i know i'm here). It can then use that correction algorithm to correct the positions of other receivers.

    Of course doing that part on-the-fly is a bit more difficult (read expensive) because now you have to invest in radio communications back and forth between the two or more receivers - but it's often done. There are even services that have base stations set up across the country that sell a subscription-based service for that purpose.

    Most times, survey firms just log the data and correct after-the-fact back in the office from the base station (the differentiator) located in the same area.

    All in all, S/A only imposes the error to systems that don't have the capability == money to do DGPS.
  • by nurb432 ( 527695 ) on Wednesday March 19, 2003 @08:30AM (#5543259) Homepage Journal
    I guess we all just pospone that trip to the wilderness to get away from things..

    Take a MAP ( remember those things? ) on your next road trip...

    After the war the service will return to normal.

    Besides, who said we had a right to use GPS anyway?
  • GPS jamming (Score:5, Insightful)

    by g4dget ( 579145 ) on Wednesday March 19, 2003 @08:31AM (#5543266)
    I suspect the Iraqis have little need of GPS--their military probably knows their country pretty well and they don't have much in the way of smart weapons.

    GPS is much more important to the US military, which does not have on-the-ground knowledge there. The US should be more worried about the Iraqis jamming GPS signals and other communications.

    Of course, so far, it looks like Iraq is pretty feeble militarily. I suspect the war will be over very quickly. Which brings up the question again: why are we going?

    • Re:GPS jamming (Score:4, Interesting)

      by dachshund ( 300733 ) on Wednesday March 19, 2003 @09:26AM (#5543460)
      I suspect the Iraqis have little need of GPS--their military probably knows their country pretty well and they don't have much in the way of smart weapons.

      On the contrary. The Iraqis' biggest weakness in the first Gulf War was their inability to navigate through the open desert. There's very little in the way of navigation aids out there, so it doesn't matter how well you know the country.

      GPS is their ticket off of the roads, allowing them to do what we did-- go right through the unposted desert. My question is how much this signal will be degraded, and whether it will seriously hinder efforts at desert navigation.

    • Re:GPS jamming (Score:3, Insightful)

      by sql*kitten ( 1359 )
      GPS is much more important to the US military, which does not have on-the-ground knowledge there. The US should be more worried about the Iraqis jamming GPS signals and other communications.

      Actually, given the satellite photos, reconaissance aircraft and special forces, the US/UK probably know Iraq better than most of Iraq's Generals by now. Look at who's in charge on either side: the Allies have professional soldiers with decades of experience on the ground in wars, peacekeeping, exercises etc all over
  • by Void ( 2442 ) <> on Wednesday March 19, 2003 @08:36AM (#5543281) Homepage
    Before and after the previous Gulf War, we had S/A "jamming" by the military, resulting in "errors" of about 10 to 100m.

    During the last GW however, the US military disabled the jamming, because they were unable to produce military grade GPS receivers. They gave "normal" civilian GPS receivers to officers and disabled the jamming, thus defeating the entire purpose of the S/A system...

    This was one of the reasons they turned it off a couple of years ago.
  • But (Score:3, Funny)

    by secondsun ( 195377 ) <> on Wednesday March 19, 2003 @08:45AM (#5543304) Journal
    All you need is the nuclear missile and the 100m doesn't matter anymore.
  • by Bowdie ( 11884 ) on Wednesday March 19, 2003 @09:11AM (#5543390) Homepage
    For all your GPS news and status. []
  • by CharlieG ( 34950 ) on Wednesday March 19, 2003 @09:22AM (#5543444) Homepage
    This has been discussed before.

    Look at

    They say it will NEVER be turned back on

    also see
  • by Nyght_shadow ( 659640 ) on Wednesday March 19, 2003 @09:39AM (#5543544) [] has posted an interesting FAQ on the war and GPS. It's located here [] . It was written by Richard B. Langley from the Dept. of Geodesy and Geomatics Engineering at the University of New Brunswick. It's a good read and answers a lot of questions about GPS and general and possible routes the military can use.


  • by ahess247 ( 209933 ) on Wednesday March 19, 2003 @09:48AM (#5543600) Homepage
    It has been the policy of the Interagency GPS Board that Selective Availability would never be turned back on, mainly because there are so many civilian users the rely on the more accurate signal since it was turned off. It would be a huge public relations blunder for the government if it did.

    But before SA was turned off, the Air Force had to develop a capability called "Selective Deniability" that would allow it to alter the accuracy of GPS signals over designated theater of operations. I seriously doubt that SA will be re-enabled systemwide.

    Someone on a listserv I belog to send the URL of this PDF dated 13 March, 2003 that adddresses some of those questions. The URL is ort/2003/iraq-and-gps_faq.pdf [].
  • What about WAAS? (Score:3, Informative)

    by n1ywb ( 555767 ) on Wednesday March 19, 2003 @10:08AM (#5543725) Homepage Journal
    For those who aren't familiar with WAAS, it's the Wide Area Augmentation System. It's like DGPS on speed. It's run by the FAA. They have a dozen receiving location scattered around the country, at precisely surveyed locations. They measure the difference between where the GPS satelite says they are, and where they actualy are, and then transmit that information to geostationary satelites, which then beam the info back to earth. In a nutshell you get 3m GPS accuracy.

    AFAIK there is no provision for reducing the accuracy of WAAS without just turning it off. The FCC would really like to use WAAS to enable planes to do instrument landings at airports without ILS. Of course the FAA can just turn it off anytime...

    WAAS works great though. I've left my GPS on auto-detailed track mode, and I've inadvertantly created a highly accurate map of my campus just by walking around with my GPS in my pocket :)
    • Re:What about WAAS? (Score:3, Informative)

      by Oswald ( 235719 )
      The Area of the Service is Wide, but only by comparison to the Local Area Augmentation Service(LAAS). It doesn't include Iraq.

      As for leaving it on to help in the U.S., the system is not yet certified for aviation.

      Here's [] a page that says basically the same things.

  • by EriktheGreen ( 660160 ) on Wednesday March 19, 2003 @10:36AM (#5543877) Journal
    See (lazy me, cut and paste from a google news post): ity.htm gps_pdd.htm _SA_Event_QAs.pdf

    In short, NO, they won't degrade GPS.

    I dunno what's more disappointing, that some lamer submitted this to slashdot, or that more of you supposedly "Educated" geeks don't challenge the idea.

  • Precision Ag (Score:3, Interesting)

    by Tsu-na-mi ( 88576 ) on Wednesday March 19, 2003 @10:54AM (#5543992) Homepage
    I for one couldn't care less if hikers' GPS accuracy is reduced to 100m, but for the industry I work in (Precision Agriculture), this presents a huge problem. Many of our clients used DGPS back in the day, and in some areas where it is freely available (along the coast, mostly), still do. However, most do not. 3m was already bad enough, but 100m is a real problem. I'm sure there are other industries being affected by the use of SA as well.
  • by Xformer ( 595973 ) < minus bsd> on Wednesday March 19, 2003 @11:32AM (#5544238)
    According to this article [], nothing needs to be done to the satellites at all. Jammers can be deployed to scramble civilian GPS signals over a localized area.

    After all, when's the last time you've seen a GPS receiver with a dish antenna? Ground-based signals can logically affect them just as easily as sky-based.
  • by mark-t ( 151149 ) <markt@nerdfl[ ]com ['at.' in gap]> on Wednesday March 19, 2003 @12:25PM (#5544577) Journal
    I know a guy that's legally blind, and uses his GPS every once in a while to confirm his location -- specifically, he sometimes needs to confirm where he is at from time to time. This is particularly important when he is travelling to an address he has not been to for some time. A computer-synthesized voice tells him almost exactly where he is, in terms of the streets and avenue names of the city as well as an address range. This guy is amazingly self-reliant for someone who is blind, in my opinon (he actually isn't completely blind, but he can't make anything out other than blobs of color that are more than a few inches from his face).

    Now correct me if I'm mistaken here, but wouldn't deliberately decreasing the accuracy of GPS signals essentially create a further handicap for this person who uses the equipment in his day to day life to function more like a "normal" person. Somehow that just seems wrong to me.

    And on the up-side, it's great news for people who don't want the rental car companies tracking where they drive.

  • by jvaigl ( 649268 ) on Wednesday March 19, 2003 @12:28PM (#5544599) Homepage
    It's an interesting discussion, but doesn't look like it's going to happen. The article they're referring to is just some German auto club that says the thing maybe it could happen when the war starts. Hardly authoritative.

    The official sites to monitor if you're worried: []: The IGEB is a senior-level policy making body chaired jointly by the Departments of Defense and Transportation. Its membership includes the Departments of State, Commerce, Interior, Agriculture, and Justice, as well as NASA and the Joint Chiefs of Staff.

    Right after 9/11/01, they posted (still there) this: "GPS Selective Availability (SA) has not been used since its deactivation by the President on May 1, 2000. At that time, the United States Government stated that it has no intent to ever use SA again. There has been no change in this policy." [] is the official source for notices to civilian GPS users about schedule satellite outages, etc. They have nothing related to S/A being turned back on, and they certainly would if it were going to happen.

    We can jam or dither the civilian code over the theater if we need to.

  • by plopez ( 54068 ) on Wednesday March 19, 2003 @02:48PM (#5545877) Journal
    The comapny I am currently working for (an Env. Engr. firm) requires 15m accurracy for field work. We work with a number of large energy companies, state and federal regulatory bodies and we even are working with DOD and Army Corps of Engineers. If we cannot get good readings, we (and our clients) are out of compliance. Also, doing groundwater studies with 100m to 300m accurracy is also unreasonable.

    GPS has become so embedded in our society, that this move just isn't viable anymore, IMO.

    Is anyone else in this same situation?

The intelligence of any discussion diminishes with the square of the number of participants. -- Adam Walinsky