Differential GPS: is this in use?

According to Wikipedia, Differential GPS is a method for correcting the standard GPS signal. While GPS has a error of roughly 10 meters, by comparing where GPS says you are to a known location, you can "correct" this difference and essentialy eliminate what little innaccuracy there is in the system.

The best system availible seems to be John Deere's "Starfire," which offers 4.5cm accuracy over a fairly broad area:

en.wikipedia.org...

Combine this with the GPS guidance systems currently availible (we can fit GPS/INS and control mechanisms inside 8 cubic inches for $3,000... I'll try and find the link) and we have the potential to build small and affordable weapons with accuracy matching laser/IR guided weapons.

With 4.5cm accuracy you could use little or no chemical explosives... kinetic energy alone would do the trick, and you'd have almost no colarotal damage. This would be perfect for many of today's conflicts.

Yes, absolutely. DGPS has been around for a long time. Lots of GPS receivers support it.

www.gpsinformation.org...

You can even "do it yourself" if you have lots o' bucks. You need a very pricey reference GPS receiver and a site survey accurate down to less than a centimeter to place the antenna. Then you send out the difference between what the navstar constellation tells you, and where you know the antenna is, to your users. That's how dgps works, more or less.

Originally posted by Tom Bedlam
Yes, absolutely. DGPS has been around for a long time. Lots of GPS receivers support it.

www.gpsinformation.org...

You can even "do it yourself" if you have lots o' bucks. You need a very pricey reference GPS receiver and a site survey accurate down to less than a centimeter to place the antenna. Then you send out the difference between what the navstar constellation tells you, and where you know the antenna is, to your users. That's how dgps works, more or less.

From Wiki's differential GPS article, there's a number of systems availible and most commercial GPS systems feature differential GPS correction. What I was wondering is if any of our GPS-guided weapons (JDAM, Excaliber, SDB, etc.) took advantage of d-GPS for increased accuracy?

Ah, you're making ol' Tom get that queasy feeling. (peeks..ok it's published) um NO is the answer in short, because they don't need to. [ps...it's been a long time since I did any GPS stuff, I called an expert: there was a military DGPS added to block II! They insert an encrypted correction into the almanac data block, which corrects to something better than 20 cm (mil only). The largest residual error is local tidal deformation! There are something like 8 correction receivers in the US, one is at Kirtland.]

The military has access to the M codes and the other frequencies. If you have L1 and L2 C (civilian) you can get nearly as good as DGPS, but with dual (or multi) frequency receivers, you can figure out nearly all the variables and correct for them.

ps That

Yes,

The Fire Scout that will be deployed in groups of 3 on the new LCS uses DGPS for guiding GPS munitions including the RGM-109E.

That is one of many examples.

DGPS is commonly used in surveying land. Many consumer sports gps devices use DGPS.
A GPS receiver need to receive 4 satellite signals to get an initial position fix. The fourth satellite is needed to calibrate the internal clock in the receiver. After the initial position is calculated, It can track by 3 satellites with an accuracy 10m to 30m depending on your latitude. The main cause of the inaccuracy is due to atmospheric conditions. storm clouds can block a signal and an approaching weather front can refract the signal. DGPS uses as many satellites combinations as possible to calculate locations and then averages the locations. On the consumer receivers with 12 channels, this could return anywhere from 4 to 220 locations, so the internal calculations can take several minutes. Most Sports GPS receivers use a slow cpu to conserve battery life, but a cruise missle can have a much faster processor.
An alternate is WAAS. This uses reference signals from known locations to calculate an error adjustment value that is applied to the calculations.

I thought all trans-oceanic liners used DGPS in synch with receivers on shores.
At least tahts wht they taught us in class!!

mylar blankets render the wearer invisible to IR so it's going to take more than hooking up gps to ir to make a weapon effectively stealthy.