Hundreds of archaeological relics are being uncovered by a laser reading technique that can see through trees to reveal the landscape hidden by forests.

Trees and undergrowth are stripped away by the aerial detection system to show the remains of structures. Among the features uncovered by the system are a missing section of Offa’s Dyke, a Roman road and suspected Iron Age field networks.

The technology, called lidar, bounces laser beams off the ground from an aircraft 3,300ft (1,005m) above and records the minute differences in time it takes for the light to return to build up a three-dimensional picture of the landscape beneath the trees.

The system uses specially designed computer software to distinguish between the laser light bouncing off leaves and the light bouncing back from the ground. The technology dates back to the 1960s but it is only in the past five years that it has been sufficiently well developed to allow archaeologists to start mapping land covered by forests.

It is expected to reveal thousands of previously unknown or unmapped ancient settlements, fortifications, farms and features in Britain over the next decade. Lidar is a laser version of radar, and was tried out at Welshbury in the Forest of Dean, Gloucestershire, where an Iron Age hill fort was known to be hidden by trees. With the trees stripped away by lidar, the embankments of the hill fort were clearly defined.

About 12 per cent of Britain is covered in woodland. Lidar has the potential to uncover every archaeological feature still hidden by trees and undergrowth. Three forest regions have been surveyed so far with images from the 280 sq km (108 sq miles) of the Forest of Dean and 42 sq km of Savernake Forest in Wiltshire complete and the data from part of the Wyre Forest still being analysed.

Scientists from the Forestry Commission are leading the project in partnership with the University of Cambridge, English Heritage and local authorities. Peter Crow, of Forest Research, said that the system had already revealed hundreds of archaeological features, many of them previously unknown both in location and purpose. “We’ve now got a mechanism to look through the leaves and see the landscape,” Mr Crow said.

Jon Hoyle, an archaeologist at Gloucester County Council, said that lidar had revealed a host of features in the Forest of Dean, including a 200m section of Offa’s Dyke that had remained unmapped, and remnants of coal and charcoal workings.

Mysterious square structures that could represent medieval forest coppicing boundaries, and some earthworks that are believed to be Roman or Iron Age, were among the finds.

In the Savernake Forest, the route of a Roman road was uncovered, and by getting an aerial view archaeologists were able to work out that mysterious 17th-century pits found in woodland were probably boundary markers used by farmers.

Ben Lennon, who works for the Forestry Commission at Savernake Forest and the Forest of Dean, said: “For so long woodland has been a black hole for archaeologists because of the difficulty in surveying them with all the trees and undergrowth. This system is opening them up and allowing us to see the historic landscape.”

Tim Yarnell, a Forestry Commission archaeologist said: “There are undoubtedly many other archaeological sites in our woods and forests that we don’t know about or which have been forgotten with the passage of time. Lidar technology gives us a wonderful opportunity to discover, or rediscover, some of these sites.”

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