Testing the Chase - LiDAR
The basic principle of laser scanning as a survey tool relies on the ability to calculate the time taken by a beam of light to travel from the sensor to the reflecting surface and back. The sensor scans in a direction perpendicular to the direction of flight, creating a swath of point measurements.
Lidar capture animation Airborne Laser Scanning is a remote sensing technique that allows the collection of topographic information (ground height data) over large areas of landscape using a sensor mounted on a plane or helicopter.
Two types of data are collected by the sensors in this process, the height of points and the intensity of the signal reflected back. The intensity of the reflected signal depends on the type of material it reflected off. This can help us document the type of material and this indication of material coupled with the height data can help us to locate and remove the vegetation from the terrain model revealing the ground surface beneath. The process of removing vegetation gives a distinct advantage over photographic survey where visibility of ground surface is restricted by forested areas. It also allows a non-invasive, remote survey which is particularly suited to remote areas of environmentally sensitive habitat for wildlife.
The cloud of data points collected can then be used to create high-accuracy surface models of the landscape. These data, usually collected for environmental or hydrological purposes, have also proven to be exceptionally useful for identifying archaeological features.
Unlike aerial photography or digital spectral imaging, ALS is an active remote sensing technique, (meaning that measurements are taken using light emitted from the sensor unit rather than the reflection of natural light) which enables night-time data collection.
LiDAR reveals features on the ground but it cannot distinguish what these features may be, this is where our volunteers come in. Volunteers, after training, will be equipped with a bespoke app loaded on to tablets, to verify some of the possible archaeological features identified in the LiDAR survey. Comparing the features to Ordnance Survey maps, historic maps, aerial photography and previous archaeological records, our volunteer field team will support the Historic England investigators in ‘ground testing’ the survey results.
Volunteers will receive full training, equipment and support for the field work, including First Aid training. As part of the project we will have developed a special Field Recorder App to support our volunteers in the field.