GPS Accuracy Could Start Dropping In 2010 210
adamengst writes "A US Government Accountability Office report raises concerns about the Air Force's ability to modernize and maintain the constellation of satellites necessary to provide GPS services to military and civilian users. TidBITS looks at the situation and possible solutions."
That's OK. By then GLONASS will be fully operation (Score:3, Informative)
That's OK. By then Russian GLONASS will be fully operational and both the Europeans and the Chinese are thinking of launching their own satellite navigation systems. Out of these three, chances are at least one will be available for the US to use in case of a global conflict.
Re:Surveyors are going to start having problems... (Score:3, Informative)
No they wont. http://surveyorsnotebook.com/ [surveyorsnotebook.com] If I were to purchase a plot of land ad it had gps coordinates as the buoundary then they would be hiring a certfied surveyor to redo it. GPS is great for maritime , road, and outdoor navigation but is no where near accurate enough for surveys.
Well not if you just walk around with an etrex, but surveyors have more accurate gear than that. Not sure if they still use differential GPS though.
Re:Hardware can fail? (Score:3, Informative)
Actually the GPS satellites aren't failing fast enough. It's my understanding that the Air Force has multiple satellite sitting on the ground waiting to launch but the ones on orbit aren't dying fast enough (some of them are already at twice their design life and still going strong)
I was also under the impression that there are currently 29 satellites in orbit, which means that 5 would have to fail before we even get down to a constellation of 24, and they can launch spares before that happens!
Re:How much is actually going to be lost? (Score:5, Informative)
solar event will cause transient events that will recover in a few seconds.
GPS2F was awarded in the early 90s with a launch date of more than 10 years out. This caused parts issues that significantly magnified design issues. Without going into company secrets, let's just say that bean-counters and engineers fought long and hard. I wonder why Boeing lost GPS3...
If LockMart can't deliver as promised, Airforce can always buy more IIF. After 12-or-so builds currently on contract by Boeing, you figure even the incompetent can get their bugs worked out by then (sans part issues)
Re:Surveyors are going to start having problems... (Score:3, Informative)
Btw, IAAS
Re:Surveyors are going to start having problems... (Score:2, Informative)
Doesn't matter.. you aren't going to get better than 10m accuracy without DGPS and 1m with it. Surveys have to be right to centimetres - no GPS can do that (possibly some of the military stuff, but I'd be surprised if even they were that accurate).
You are simply wrong. RTK GPS is accurate to a centimeter. Surveying, however, relies on a benchmark, which means that you won't have centimeter accuracy unless the benchmark is perfectly recorded, perfectly preserved, and can be found perfectly a second time.
Re:Surveyors are going to start having problems... (Score:5, Informative)
You don't need military GPS to be that accurate, it can be done with differential phase GPS. See: here [wikipedia.org]. By using a fixed base station at a location with known coordinates, one can expect to see accuracies in the 1 to 2 cm range as long as the receiver is within 10's of km from the base station. There are several manufacturers who make gear that can achieve this level of accuracy, see Leica [leica-geosystems.com], Magellan [magellangps.com], and Sokkia [sokkiacanada.com]. I've been using Leica gear at work mostly, and have see ~1cm accuracy under good conditions pretty consistently. A lot of legal surveying in remote areas is done exclusively with GPS, especially in the northern parts of B.C and Alberta. I've done legal surveys with GPS in the Vancouver area, but getting high accuracy in urban areas is more difficult because of multi-path noise and qoor signal quality from obstructions such as buildings. Also people in the city get mad when you cut down trees to get better reception ;)
Re:Just in time for Galileo (Score:3, Informative)
I'm Catholic you insensitive clod! I can't use it!
Get with the times, you anachronistic clod!
Thanks to his intuition as a brilliant physicist and by relying on different arguments, Galileo, who practically invented the experimental method, understood why only the sun could function as the centre of the world, as it was then known, that is to say, as a planetary system. The error of the theologians of the time, when they maintained the centrality of the Earth, was to think that our understanding of the physical world's structure was, in some way, imposed by the literal sense of Sacred Scripture....
â" Pope John Paul II, L'Osservatore Romano N. 44 (1264) - November 4, 1992
http://en.wikipedia.org/wiki/Galileo_affair#Modern_church_views [wikipedia.org]
In 2000, Pope John Paul II issued a formal apology for all the errors of the Church over the last 2000 years including the trial of Galileo among others.
Re:Surveyors are going to start having problems... (Score:5, Informative)
Even when trying to take a fix on the same point over time, the margin of error is random. Most of the error is due to propagation delays of the signal. The atmosphere is constantly changing density - the jet stream can raise or lower air pressure between you and satellite #5 at this point in time, or between you and satellite #23 at another point in time. The ionosphere can cause delays or reflections. Nearby buildings, or cars, or airplanes can cause ghost signals. Remember your high school physics teacher who always qualified the the speed of light with the phrase "in a vacuum"? It really makes a difference.
Remember, the GPS satellites are flying in lower earth orbits, and are constantly moving over and around you. They are not fixed relative to you the same way a geosynchronous satellite is (like the DirecTV satellites.) So even if the weather patterns could be precisely measured and figured out, they would be meaningless as soon as the satellite moved - and they're always moving very, very fast.
Differential-GPS improves accuracy by having a mounted GPS receiver at a precisely surveyed point, then transmitting (via FM) the "error difference" between what is derived from the GPS system and the surveyed coordinates. If the error at a particular time is 3 meters at the DGPS antenna, then the error at any other GPS receiver in the area is probably pretty close to 3 meters at that same time (assuming the weather patterns are similar between you and the DGPS antenna.)
You can indeed leave a GPS fixed in a point and average the readings to reduce the margin of uncertainty, but you'll never achieve the high accuracy needed for surveying.
Re:Surveyors are going to start having problems... (Score:3, Informative)
The engineers at Trimble would probably take issue with that statement, since they sell high-dollar ($10~$100k) survey equipment that produces reliable >0.1' accuracy (wikipedia states 20mm as a working number). I worked with equipment in 2003 that was at least 5 yrs old then, and it was that good. The key, as other posters have mentioned, is a base station and some fancy calculations that make it possible.
I'm pretty sure that this equipment has been around since well before the Clinton administration ended the obfuscation/degradation of GPS signals; it just isn't practical for your typical consumer gear.
Re:Surveyors are going to start having problems... (Score:3, Informative)
That is why surveyors buy surveyor GPS gear. The shit ain't cheap, but when you want centimeter accuracy, you have to buck up.
http://www.trimble.com/survey/GNSS-Surveying-Systems.aspx [trimble.com]
Basically, you set up your own local differential GPS station that sits for a while and figures out its position to a very high degree of accuracy.
You then use very accurate devices capable of sub meter accuracy with time averaging and DGPS, and use the signal from the local station to get even better accuracy than that.
Getting accurate positions for surveying isn't that hard, since you can time average, add local DGPS stations and correct the data even after its been collected. You just need the gear.
Now if you want real time tracking with sub meter accuracy, that is very hard.
Re:Best not one system... LORAN, Fuller, Cold War (Score:5, Informative)
A friends mom escaped the wreck of a 90ft Fish Packer as it hit the rocks at night in a passage with strong currents due to a problem caused by relying on GPS. It was due to something like how it derived the heading vs the direction of travel or some-such.
Something wrong there. Both LORAN and GPS only give position (GPS gives time too, but that doesn't help here). Direction of travel is determined in both systems by taking the difference in position over a known time interval. GPS can give heading by using the phase difference between receivers on different parts of the vessel, whereas the wavelength of LORAN was probably too long for that to work. Upshot is, a problem involving headings and direction of travel isn't the fault of GPS, and using LORAN would have been no defence. It may have been a problem with the GPS receiver software, but LORAN calculations could go wrong too. Most likely it was a navigator not understanding the systems they had.
Re:Europe to the rescue! (Score:3, Informative)
Re:Surveyors are going to start having problems... (Score:4, Informative)
Re:Surveyors are going to start having problems... (Score:5, Informative)
The DGPS system at Libby Dam in Montana is accurate to 1-mm vertically:
Performance Monitoring Of Libby Dam With A Differential Global Positioning System [3dtracker.com] UNITED STATES SOCIETY OF DAMS (JUNE 2005)
More than GPS (Score:5, Informative)
Here's a listing of all current/proposed global systems. Regional only systems such as IRNSS or Beidou1 are not listed.
GPS - United States - Fully Operation
Galileo - EU/China/Israel/South Korea/Norway/Etc - 2013
Beidou2/Compass - China - 2012?
GLONASS/ - Russia/India - Complete in 2010