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See how the land lies

Flood risk can now be assessed with astonishing accuracy thanks to a new three dimensional mapping technique launched last month. Mark Hansford investigates.

Ordnance Survey has launched its own take on Star Wars, using airborne laser technology to provide extremely detailed 3D digital maps.

The technology, developed in partnership with the Environment Agency and e-business software specialist InfoTerra, generates models that closely match every manmade or natural undulation on the ground, including trees, buildings, quarries and landfill sites.

LIDAR (light detection and ranging) systems work by sending a laser pulse from a carrier aircraft to the ground and measuring the speed and intensity of the returning signal.

A 3D digital elevation model of the landscape is created by interpolating the distance travelled by each laser pulse and the exact position and orientation of the aeroplane coincident with each pulse emission. This position is calculated using an integrated global positioning and inertial navigation system.

The result is a model accurate to within 190mm.

The Environment Agency has invested heavily in the system, and as a result major flood plain areas, coastlines, urban conurbations and river valleys are already available as LIDAR data.

Anywhere else in the country can be recorded to order.

'The beauty of LIDAR is that you can see the exact effect of increases in sea or river levels, ' explains an Ordnance Survey spokesman.

'In light of the recent increase in flooding throughout the country, this is likely to prove an invaluable tool, not only for the Environment Agency in planning defences but also for insurance companies, builders and developers, ' he says.

LIDAR's use is not limited to flood defence either. Planning for new developments and road schemes can also benefit as, when overlaid with Ordnance Survey's highly detailed 2D topographical data, it clearly displays the visual impact that new features will make on the landscape.

'Combining LIDAR with the land line data brings the whole model to life, ' says Ordnance Survey's land form product manager Kirstie Bulpitt.

As with any new technology, LIDAR does not come cheap, at a minimum cost of £250 per square kilometre. However, turnaround time is fast, with just 42 days needed to produce a DEM from scratch or 28 days to provide existing data.

'For accurate digital data, cost is always a factor, ' explains Bulpitt. 'But viewed against the potential savings of avoiding or preventing serious flooding, LIDAR is not only valuable but also extremely cost effective.'

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