LiDAR (light detection and ranging) is a survey technique which transmits laser pulses from a plane to the ground. Using the principle of measuring distance through time, the returning reflection records the location of surface points with a high degree of accuracy using geographical positioning systems.
The 3-dimensional co-ordinates are used to produce digital models of the surface – from the highest point that the laser hits (first return) through to the lowest point (last return).
If just the last returns are modelled, the tree canopy and vegetation are stripped away to reveal the shape of the ground. This shows up earthworks such as hollows, mounds and lines of banks, revealing archaeological features previously unseen. LiDAR is therefore particularly useful in heavily wooded areas.
Within the High Weald AONB, LiDAR has been flown for the Weald Forest Ridge and can be viewed here.
Download from English Heritage for more detailed information on LiDAR.