LiDAR

LiDAR stands for 'Light Detection and Ranging'. It's a light survey technique which archaeologists use to measure the distance from a sensor to the ground. They use it to create accurate models of the landscape.

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Two images, one above the other. The top image shows woodland from above, while the image below filters out the trees and shows a mixture of blue and yellow colouring across the landscape.

LiDAR image showing Farningham Woods, a possible Roman site. The image at the top shows the trees, while the image below has had these filtered out.

How does LiDAR work?

LiDAR technology measures distance by using light waves. It records the speed and intensity of a pulse of light fired from a sensor towards an object or surface. The light bounces back, sending a return signal to the sensor. This creates an accurate 3D picture of a surface.

As the pulse of light can sometimes penetrate tree branches and other plants, it also allows us to see features in woodland from above.

This image shows how LiDAR can penetrate trees and woodland. The top image shows the trees in Farningham Woods, a possible Roman site. The image underneath shows features underneath the tree line.

A greyscale image showing a white ring around a central white mound (a Bronze Age barrow).

A LiDAR image showing a possible Iron Age fort on the top of Otford Mount through a tree canopy. There is a Bronze Age barrow in the centre of the image (the white mound).

What does a LiDAR image look like?

LiDAR images can often be very colourful, or they can use the contrast of black and white and shading patterns to show the height of features in the landscape.

In this image the features which are raised, like the banks, are shown in white. Sunken features, like ditches and pits, are shown in black.

A greyscale image showing a long dark line (a Roman road).

A long stretch of Roman road running from London to Lewes in Sussex lies to the west of the Darent Valley. The road can be seen in the woodlands of Limpsfield in this LiDAR image.

LiDAR and the Roman Darent Valley

One type of feature that LiDAR can be very useful in revealing are Roman roads. They often appear as long straight lines in the landscape, sometimes two parallel lines. These represent the drainage ditches which were either side of the raised road.

This image shows a Roman road which ran from London to Lewes in Sussex. It lies to the west of the Darent Valley.