THEY have lain hidden beneath the Hampshire countryside for thousands of years.

But Bronze Age burial mounds and other ancient artefacts have finally re-emerged – thanks to a laser-imaging system that has enabled experts to unlock the secrets of the past.

The New Forest has become the first National Park in the country to have its entire landscape surveyed using the revolutionary new technique.

More than 3,500 previously unknown archaeological sites and monuments have been discovered, including prehistoric field systems and an Iron Age hill fort surrounded by a defensive system of banks and ditches.

The new research has also shed new light on two Bronze Age barrows on Beaulieu Heath.

They were damaged when a rifle club built a new target range on the site in the 19th century – and the mapping shows how misshapen one of the barrows is compared with its neighbours.

The New Forest National Park Authority (NPA) said experts surveyed an area of 350 square miles.

Many of the previously unknown landmarks were hidden under dense forest but NPA staff used harmless laser beams, fired from an aircraft, to build a 3D map of the landscape.

The Light Detection and Ranging (LiDAR) system can penetrate tree canopy, revealing features that cannot be seen using other means.

Lawrence Shaw, heritage mapping and data officer for the NPA said: “These resources will allow the public to explore the National Park in a way they could never have done previously.”

How LiDAR works

INTERPRETING “lumps and bumps” on the ground shows how the New Forest has been used since the Neolithic period.

Finding and recording archaeological features using traditional field surveys can be a difficult and time-consuming task but LiDAR makes it possible to speed up the process.

A pulsed laser beam fired from an aircraft records thousands of three-dimensional images every second.

The pulses bounce off the ground and are received by detectors on the plane, enabling experts to create a digital profile of the landscape.

An NPA spokesman said: “Because the pulses can filter between the leaves and branches of trees we’re able to strip away the vegetation and look at the ground and the archaeology beneath the tree canopy – often with spectacular results.

“These and other techniques help us to accurately identify and interpret sites, which can then  be checked on the ground.”