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GPS Used To Monitor Continental Drift
metz2000 writes "BBC News is reporting that a team of scientists from Nottingham (UK) are using GPS to measure sea levels and continental drift. The team has around 50 stations across the UK, and use GPS technology to track miniscule changes in altitude and location. This allows the team to gain an understanding of how the UK landmass is likely to change over the coming centuries. They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'."
I guess that they are using differential GPS, by which the time delay at a known location is compared to the time-delay at the location of interest. This enables for very accurate estimation of where you are.
On the other hand, at least in California (where they have a GPS network for earthquake monitoring), the network might well be permanent, hence you can do a nice sort of averaging over time. We have found that even with normal GPS, you get nice accuracies over a time period.
From "Navigation Satellites & GPS v2.2.3 / 01 dec 02 / gvgoebel@earthlink.net /"
Geophysicists have been exploiting GPS since the mid-1980s, using it to measure continental drift and the movement of the Earth's surface in geologically active regions. They have been able to obtain accurate surface measurements to within a few millimeters through a procedure known as "carrier tracking", which is even more accurate than differential GPS. Carrier tracking actually senses the phase of the carrier signals on which the location code sequences are broadcast. It is, not surprisingly, a tricky and subtle procedure, and not applicable for general use.