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'."

Comments

Solution?

[ahadley]

well this should sort the north/south divide and tilt (apollogies for pun) the house price difference to the north.....

just my 2 (euro) cents worth

Alex

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.

Re:Accuracy

[d-Orb]

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.

Re:Accuracy

[asmithumd]

Back in the late 80's I had some college rooommates who did this for a living. After moderate earthquakes in southern California, groups of geophysics graduate students would be sent to the channel islands off the coast with huge old clunky GPS receivers. They would align the GPS receiver over a benchmark and camp out for 3 days collecting data. Similar groups would do the same thing all over SoCal. Combining the data makes for a super differential GPS data set. As each receiver is at a known location (well sort of, it is what they are there to determine), each has the accuracy of a single diff. GPS receiver. However, what the scientists cared about was not the aboslute positions of the receivers, but their relative positions. As I recall, 0.5cm resoultion was routinely achieved event back then. I'm sure todays systems are automated, and remotely read out. Today's grad students won't have stories about being buzzed by navy jets or herds of ferrel cats.

Re:Accuracy

[hughk]

First of all, now that Selective Availability has been disabled, stationary GPS can easily give accuracy down to a couple of metres or better. However, even when SA was enabled, surveyors could always get cm level data out of a GPS simply because they could leave the station sitting and let it average out the passes. If you are building a road, you normally want to fix it down to the cm level, because it is embarrassing when a bridge, for example, doesn't fit. Any major construction project has at least one well known point from which the land survey is based. This point connects the survey coordinate system with a general coordinate system (such as latitude and longitude from WGS84). This used to be done optically but over the last 15 years or so, GPS has been used and has performed well.

For continental drift, they need mm level data. I guess, they just leave the station for a longer time to get even more passes.

Re:Accuracy

[Yet Another Smith]

They're doing very high-precision work which doesn't look at the code, but the actual waveform, using static (hours-long) occupations of benchmark monuments. Then custom software is used to work out sub centimeter (often 3-5 mm) locations in post-processing.

This sort of thing has been done in a number of locations. I've been involved with studies like this in Nevada and Italy.

It's hardly suprising that Scotland is rising and England is sinking. The phenomenon is known as 'isostatic rebound' and happens any time a substantial load is removed or added to an area. The massive ice-age glaciers over Scandinavia caused that area to sink and the 'low countries' - especially Holland - to rise. Now that the glaciers are gone, Scandinavia is rising again and the Netherlands are sinking into the sea. The same is probably happening on a smaller scale to Great Britain. In the US, the Appalachian Mountains are eroding away, causing them to rise, and the coastal plains and Mississippi delta, where that sediment is being deposited, are sinking.

This is all a very slow process, millimeters per year, but over time it makes a big difference.

Damn...

[nmg196]

...you tell me this *after* I've just bought a house in Southampton. Bummer. I knew the must be *one* good reason to live in Scotland...

Nick...

For those interested...

[heli0]

..in how they use GPS to make such precise measurements you can read about it here:

Using GPS to Separate Crustal Movements and Sea Level Changes at Tide Gauges in the UK

Application of the Dual-GPS Concept to Monitoring Vertical Land Movements at Tide Gauges

Accuracy

[ljavelin]

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.

In related news ....

[Surak]

..some scientists studying the "sinking" effect have noted CowboyNeal's recent move to Southampton.