What is LiDAR?
LiDAR, standing for “Light Distance and Ranging,” also known as Airborne Laser Scanning (ALS), is a survey technique that has been used by archaeologists for just under 20 years now. It has aided in the discovery of new sites, and is particularly important for its ability to show archaeology beneath vegetation.
The technique works using a plane-mounted laser scanner which sends out millions of pulses of light towards the ground and detects the reflections. From this data a highly accurate “point cloud” is created of everything the light has hit on the earth’s surface. The points are then ‘classified’ for whether they are vegetation, buildings, or the ground surface; all of the above-ground points are filtered away, leaving us with a “digital terrain model” of the bare earth, which allows us to start to detect archaeology!
The LiDAR "point cloud" of Bulstrode Camp hillfort, Bucks, overlooking the Alderbourne chalk stream valley. Data from the Environment Agency.
Our LiDAR Survey
In 2018/19 we commissioned a bespoke survey of the Chilterns and some surrounding areas. At 1400 km2, it was the largest LiDAR survey ever flown for archaeology in this country, and one of the largest in the world. The survey took place over the winter, with the data available through our Citizen Science LiDAR Portal.
Why survey the Chilterns?
The Environment Agency has infact begun a program of surveys over the whole country, and their data is freely available for use, however a bespoke survey was settled on for this project for two main reasons:
- firstly, the Chilterns has not been a priority for survey by the EA as their main concern is flood risk, and the permeable chalk of the Chilterns generally has low risk of flooding;
- secondly, we have commissioned a very high resolution survey (25 cm resolution, as opposed to the 1 m resolution of most of the EA survey) which means we will be able to pick out far more detail, and therefore many more archaeological features from the survey, particularly under tree cover.
Our survey was flown and processed by Cyient Europe.
What happened after the survey was flown?
Once our contractors provided us with the data we produced a number of different ‘visualisations’, in order to make the humps and bumps show up clearly. From there members of the public were able to log on to our mapping portal, trace into our database and record all the features that they can see, from barrows and even a new hillfort!
A map showing the extent of our survey is shown below in blue, with hillfort sites represented by red dots.