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Last Updated: Wednesday, 4 June 2003, 09:28 GMT 10:28 UK
The millimetre men
Brady Haran (BBC)
By Brady Haran
BBC News Online

David Baker and Richard Bingley
Space geodesy is an exact science
When global positioning systems (GPS) were invented, they were seen primarily as tools for the military and navigators.

However, GPS is now being used in ways its creators may never have imagined, such as predicting storms, measuring sea levels and monitoring continental drift.

At the forefront of these new applications is a team of scientists in Nottingham, UK.

They work in a world where a millimetre's movement can be as important as a kilometre.

The Institute of Engineering Surveying and Space Geodesy (IESSG) - part of the University of Nottingham - stores and uses much of the UK's GPS data.

Fixed GPS stations show the UK is moving in a north-easterly direction

Every day it receives measurements from 50 or so fixed stations scattered around the UK - including one on their building at the university campus.

To formalise its role, the institute was recently named the nation's official archive of this information and received a 71,000 grant from the Natural Environment Research Council.

Data within the British Isles GPS archive Facility (BIGF) - which the scientific community can access for free - has many applications.

For example, by measuring the rise or fall of land, the nation's tide gauges can be calibrated and oceanographers can accurately measure if climate change is affecting sea levels.

Dr Richard Bingley, from the IESSG, explains: "The measurements from tide gauges are not a true reflection of changes in sea levels unless you know how much the land is moving."

There are suggestions GPS could be used to better understand the organisation of thunderstorms
Dr Richard Bingley
The GPS measurements have shown the land in Scotland is rising by about one or two millimetres a year, while the land in England's south is slowly "sinking".

"Essentially the country is tilting. By comparing this land movement and sea level measurements provided by the Proudman Oceanograqphic Laboratory, it appears that sea level has risen 10-20 cm over the last century," Dr Bingley says.

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

This is caused by rotation of the Eurasian continental plate.

Another emerging use of GPS data - and quite an unexpected application - is weather forecasting.

HMS Nottingham on rocks
GPS was initially designed for the military and navigation, but it is now evolving
Dr Richard Bingley
As scientists endeavour to get more accurate readings from GPS satellites in space, they have learned water vapour in the atmosphere "slows down" the signals transmitted by these satellites.

By measuring the amount of slow down, it is becoming possible to detect moisture before it can be detected via traditional means.

Dr Bingley said: "Work is still being done in this area... but there are suggestions GPS could be used to better understand the organisation of thunderstorms and perhaps anticipate when they will happen.

"We have already seen that GPS can show the build up of water vapour before cloud formation or a storm."

For this reason, the Met Office has become involved in funding fixed GPS stations.

The global positioning system locates latitude, longitude and altitude by using signals from a network of satellites in space
Other organisations investing in the network include the Ordnance Survey, DEFRA and the Environment Agency. The stations are typically worth 20,000.

Dr Bingley says it is interesting to note the expanding use of GPS data.

He says: "It was initially designed for the military and navigation, but it is now evolving as we move to improve the accuracy of GPS.

"The weather forecasting is a good example... as we remove the biases that affect our readings, such as these atmospheric affects, there are other groups that have use for the information which, originally, we were essentially trying to discard."

Location of fixed GPS stations in the BIGF network

Aberdeen, Aberystwyth, Barking, Blackpool Airport, Bristol, Butt of Lewis, Camborne, Cardington, Carlisle, Carmarthen, Chilton, Colchester, Daresbury, Droitwich, Dunkeswell, Edinburgh, Flamborough, Girdle Ness, Glasgow, Hemsby, Herstmonceux, Hurn, Inverness, Isle of Man (2), Kings Lynn, Leeds, Lerwick, Liverpool, Lizard, London, Lowestoft, Point Lynas, Mallaig, Morpeth, Nash Point, Newcastle, Newlyn, North Foreland, North Shields, Northampton, Nottingham (2), Osgodby, Pershore, Plymouth, Portsmouth, St Catherine's Point, Sheerness, Stirling, Sumburgh Head, Sunbury, Taunton, Teddington, Thurso, Wormleighton.

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