Satellites Measure "Bouncing" Landscapes

Britain is the first country in the world to begin such a project which, when completed, could make surveying ten times more accurate and allow big savings on large construction projects. The ‘bounce’ is caused by the tides. As the weight of water increases on the continental shelf around Britain’s coastline, the whole country sinks a little into the earth’s crust, rebounding as the tide recedes.

The problem for engineers is that the land does not sink evenly, resulting in local distortions which cause inaccuracies when satellite surveying techniques are used in construction projects.

Dr. Peter Clarke, of the Department of Geomatics at the University of Newcastle, is leading a research team which is using orbiting U.S. satellites to monitor the positions, with an accuracy of a millimetre or two, of more than 30 Global Positioning System (GPS) receivers located all over Britain. It should then be possible to estimate the ‘bounce factor’ in any part of Britain at any time of day.

Although ‘bounce’ has previously been measured in certain locations by similar techiques in the USA and some other countries, none has produced an accurate and comprehensive national map. The project, which should be completed by Autumn 2004, has received £64,000 in funding from the Natural Environment Research Council and also involves the Proudman Oceanographic Laboratory and Ordnance Survey, with help from the National GPS Archive at Nottingham University.

Dr. Clarke said: "The phenomenon has been known about for some time but it has only become necessary to measure these movements because of the increasing use of precise satellite surveying by civil engineers.

"For example, a great deal of time and money was spent during the construction of the Channel Tunnel to ensure that the two halves met in the middle at the right height. A few centimetres difference would have proved very costly to put right.

"The same principal applies to other large construction projects such as railways, dams and bridges.

"Our measurements will be used to adjust the data obtained by surveying to produce results which are perhaps ten times more accurate — to within millimetres rather than centimetres. This could significantly reduce the cost of large construction projects."