Russian officials are seriously talking about shutting down US GPS ground stations within their borders and Deputy Prime Minister of Russia tweeted on the subject.
What will happen to the GPS? My assumption would be that its accuracy will get worse, at least in some parts of the globe. If it is correct, then where, and by how much exactly?
I have previously posted this question on physics.stackexchange.com and here are two answers I have received there. They seem to be a little contradictory, though.
Kyle Kanos:
Usually ground stations are alternative points for a 3rd/4th signal
since it is a fixed (known) location. Russia, at least in the 90s,
didn't have a way to connect to the 24 satellites & depended on the
stations; I doubt that they are of any use anymore given GLONASSuser6972:
There are two types of GPS ground stations for the USA
system. Main stations about 5 around the world provide corrections to
timing data due to relativistic effects, clock drift, ephemeris, or
ionospheric delays that are timing constants rebroadcast by the
satellites to receivers for corrections. The types of stations in
Russia are for augmented gps called Global-DGPS . DGPS improves local
GPS accuracy from about 3m to 10 cm. However this lack of support in
Russia's areas only effects civilian use of the US system in those areas. The Chinese, EU, and Russian systems won't be effected."Employing a large ground network of real-time reference receivers,
innovative network architecture, and award-winning real-time data
processing software, the GDGPS System provides decimeter (10 cm)
positioning accuracy and sub-nanosecond time transfer accuracy
anywhere in the world, on the ground, in the air, and in space,
independent of local infrastructure." (gdgps.net)
Best Answer
The two answers pretty much cover it and are not really contradictory. Shutting down those stations will mean no broadcast correction signal will be available to recievers tuned to the US GPS network in that area. The other GPS systems don't use that same network - they have their own ground stations. And as Mapperz points out, there are different kinds of ground stations. The ones in Russia for the US system are for recievers (user segment), not for network and satellite maintenance (control segment). See the Wikipedia entry on the US system for details.
Nothing will happen to the US GPS network itself. Accuracy will get worse in those areas (and only those areas) covered by those ground stations shut down because a broadcast correction signal will not be available. How much is already answered - back to 3m from potential 10cm.
In theory they want to promote use of their own GPS system, and the same correction functionality in the US system has a counterpart in the GLONASS system. Recievers just have to be able to use the GLONASS ground control/correction station signal. As I recall, there is a class of units manufactured to use either or multiple systems. You're basically looking at an equipment upgrade/change for anyone who was relying solely on the US GPS system in Russia.