Airborne LiDAR

179 LiDAR profile through a Bronze Age barrow

Airborne LiDAR (Light Detection and Ranging), a type of airborne laser scanning (ALS), is a form of indirect data capture, whereby a laser beam is used to measure distances to points within the field of view of a laser scanner. The big difference between this and terrestrial laser scanning (TLS) is that the scanner is mounted in an aircraft pointing down towards the ground, typically capturing a 3D measurement every 10-200cm.
Airborne LiDAR is an excellent way of capturing surface data over entire landscapes. Wessex Archaeology work with data from archived data repositories (such as that managed by the Environment Agency) and also commission our own flights to capture new data.
ALS data can also be used to produce Digital Terrain Models (DTMs) and/or Digital Surface Models (DSMs); DTMs are usually bare-earth models with all extraneous surface features such as trees and buildings removed whereas DSMs comprise everything recorded by the laser scanner. Whilst the removal of trees and buildings is often useful, the algorithm used to do this can have adverse effects on upstanding archaeological features so it is important to choose the appropriate model for the task in hand.
These models can be used within Geographic Information Systems (GIS) for analysis and interpretation, allowing us to draw profiles across monuments and features, examine the slope or aspect of the ground surface, and conduct spatial analysis such as visual impact assessment. Advanced analytical techniques can be applied to enhance and visualise the 3D data which is then typically interpreted in a similar way to aerial photographs. TheDTM/DSMs can also be used within 3d modelling packages to produce rendered images and videos of landscapes. Approaches such as realistic and analytical lighting, archaeological reconstruction work and the inclusion of, modelled people and vegetation are used to help with interpretation and understanding.

180 Frame from a rendered animation of a virtual fly-through of the Stonehenge World Heritage Site LiDAR dataset