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'."

Accuracy

[ewithrow]

Considering a lot of GPS receivers have an error of + or - 10 feet or so, I wonder if they are using very precise equipment, or if having the redundancy of many units makes up for the rough estimates GPS satelites give.

Re:Accuracy

[Wibla]

They are probably using the military band of the GPS sattelites, which are considerably more precise than ordinary 'civil' GPS.

accurate enough

[Naikrovek]

I didn't realize that GPS was accurate enough for that...

I think i heard once that there were two types of recievers, one was more error prone, but gave you an updated location every second, the second was very, very accurate, but took over 10 minutes to get a position fix.

can anyone clue me in here?

Re:Accuracy

[rebeka thomas]

A GPS system working with satellites only has a limited accuracy. Even military ones aren't accurate enough. Using the same technology with ground based satellite analogs gives the accuracy required.

Spaceborne SAR

[d-Orb]

Slightly OT, but just to mention that imaging microwave radar (as those mounted in the ENVISAT or ERS satellites, for example) is also being used to monitor small changes in elevation, using a technique based on interferometric SAR (which is behind the Shuttle Radar Topography Mission [nasa.gov].

The benefit of using a satellite orbiting around the Earth is that you don't need to deploy all the "base stations". If you want to find out more, google for "differential interferometry" or somesuch :-)

Accuracy

[ljavelin]

From "Navigation Satellites & GPS v2.2.3 / 01 dec 02 / [e-mail] /"


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.

It depends

[k0de]

GPS accuracy is somewhat consistent among manufacturers, and is generally more accurate the more you pay for the equipment. However, there is always a margin for error. For example, Wilson's GPS Accuracy page [erols.com] states that vertical accuracy depends on "latitude (errors for vertical accuracy rapidly increase with latitudes greater than 65 degrees), receiver/antenna, local geometry/multipath and satellite geometry (VDOP)"

The real question is are the Nottingham group using high grade and control tested equipment and have they properly accounted for discrepency. Stating that Scotland is rising two millimeters a year is quite the claim.

Re:Population growth and land change

[Mr_Dyqik]

I wonder if there might actually be a measurable effect from increased usage of groundwater in heavily populated areas. This kind of thing can cause local subsidance, so I wonder if it can cause a general shift over larger areas.

Re:Accuracy

[egburr]

How are you going to use ground-based systems to tell you how far your continent has moved? If you put it on the same continent as the receiver, it will move in perfect relation to the receiver, so the receiver will always show zero movement. If you put it on another continent, does it have the range, especially dealing with earth curvature and line-of-sight issues? It seems to me a satellite system would be much better for this purpose.

Relativity

[spakka]

From the article:

GPS measurements have also allowed scientists to show that the UK is drifting about 2-3 cm each year in a north-easterly direction.

I disagree. The UK is only drifting north. Since we have no east or west pole, the east-west component of the velocity can only be stated relative to some other plate. We could just as well assert that the UK is stationary in the east-west direction, and the other plate is moving west.

Re:Accuracy

[WhiteBandit]

Nope! Instead it's us sappy undergraduate students who have to do it! That is how I'll be making some money this summer in southern CA. ;)

I think the logic is that some of the receivers are upwards of $10,000 USD, which is a very expensive toy to just have laying around, so they send groups of us students out with the receivers all day so that we basically babysit them and make sure no one touches them.

We also have a limited amount of receivers, and a large amount of benchmarks to check, so I believe we check Site 1 this day and Site 2 this day, etc...