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Tracing coastal changes to help prevent flooding.

Scientists do not have enough information to work out which areas of Britain's coastline are most susceptible to tidal flooding, according to the British Geological Survey (BGS), hence its investigation of a new airborne technique that it claims is particularly suitable for monitoring coastal and estuarine environments.

LIDAR (Light Detection And Ranging) uses a laser altimetry system to precisely measure the distance from a sensor to the Earth's surface. When combined with GPS (global positioning systems) and Inertial Navigation Systems to determine accurately the sensor's position and orientation, LIDAR can provide high precision elevation data to between ten and 20 centimetres vertical accuracy, says BGS. Depending on which LIDAR system is used, the average area covered by each data measurement varies from 0.2 to six square metres.

"If sea level were to rise by one metre, vast areas adjacent to the coastline could be flooded," says BGS senior remote sensing geologist Dr Doug Tragheim, "but we don't have enough information below the five metre contour line to know which areas.

"We've looked at some data compiled by the Environmental Agency (using its LIDAR instruments) and think it's a technique we could use in the future," he adds.

BGS has used digital photogrammetry (a means of producing digital images from aerial photographs) to monitor short-term changes in coastal geomorphology for about five-and-a-half years and it has just upgraded its system with PC-based equipment. LIDAR offers a number of advantages over the photogrammetric method, however--data can be obtained in poor light conditions, even at night, and it also relies less on expert interpretation.

It's a fact: the largest recorded hailstone weighed just over one kilogram. It fell in Bangladesh in a hailstorm that killed 92 people

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Author:McWilliam Fiona
Date:Jun 1, 1999
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