Lidar

Lidar (Light Detection and Ranging) is a remote sensing technique that is used to create accurate and precise 3D models and visualisations of landscapes. As with most innovative technologies lidar has its origins in the military where it was first developed to carry out underwater scanning to identify submarines. Lidar as a survey technique first came to the fore in the UK during the 90s when it was initially used by the Environment Agency to create terrain maps to assess flood risk. However, it was not until the turn of the millennium that the potential of lidar for archaeological survey began to be recognised.

Lidar derived DTM of a section of Ramsey Island WalesLidar derived DTM of a section of Ramsey Island Wales

In practice, a lidar survey consists of the transmission of an active laser beam from a fixed-wing aircraft towards the ground. The reflection of the beams transmitted back to the aircraft are then measured to give distance values which are used to create a 3D Digital Elevation Model (DEM) of the landscape below. The intensity of the returning beam can also give an indication of the type of material that it reflected off of. This coupled with the height data can be used to identify and remove vegetation from a DEM, which in turn offers a view of hidden features and landscapes not visible on aerial photographs. Global Navigation Satellite Systems (GNSS) or Global Positioning Systems (GPS) as it is more commonly known is also used during a survey to ensure that the 3D model is geo-located on the earth.

Illustration of lidar data capture from a fixed wing aerial platformIllustration of lidar data capture from a fixed wing aerial platform

Lidar coupled with aerial photography offers a fantastically comprehensive view of the landscape as it exists during the present and as it existed in the past. From this, CHERISH archaeologists can map and interpret historical features and begin to unravel what the wider historic landscape may have looked like in the past.

Close up view of the lidar data collected at Ramsey Island wales visualised using principal component analysis (PCA) of hillsahingsClose up view of the lidar data collected at Ramsey Island wales visualised using principal component analysis (PCA) of hill-shadings

Close up view of the lidar data collected at Ramsey, Island wales visualised using local relief differenceClose up view of the lidar data collected at Ramsey, Island wales visualised using local relief difference