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LiDAR, or Light Detection and Ranging to give it its full name, is an active remote surveying method credited with causing a dramatic shift in how scientists collate and analyze information about the Earth. It can be used to monitor the environment, map the oceans and explore the Polar regions – it has even been used to investigate the exterior of the Moon. The technique is said to be leading a revolution in archaeology, changing the ways archaeologists understand human activity of the past.
LiDAR can measure the height and ground surface, and other features of large areas of landscape with high resolution and accuracy. The technique can provide highly detailed and precise models of the land surface at meter and submeter levels, offering the opportunity to identify and record difficult to detect features. While it is widely employed in surveying the built environment to create digital models of terrain (DTM) or elevation (DEM) of specific landscapes, it also very useful for finding subtle variations on the ground, and under vegetation and forest canopies that could point to hidden relics of the past.
A NATO workshop in 2000, organized to discuss future practices in aerial archaeology, revealed the ‘earthwork survival’ of a Roman fort previously thought to have been totally leveled by plowing in River Wharfe, Yorkshire. Since then, LiDAR has been employed to reveal many relics once thought lost, including buildings and pyramids built by the ancient Mayan and Egyptian civilizations, discovered thanks to square patterns found on the ground over vegetation. The UK Environment Agency’s Geomatics Group has flown many surveying missions – including over Stonehenge World Heritage Site – and since 2015 have made all of its LiDAR data freely available as part of a move towards open data access.
How LiDAR Works
LiDAR uses pulsed laser light - either ultraviolet (UV), visible or near infrared (IR) light - to measure the distance to an object and create a three-dimensional representation with very high resolutions. In archaeology, the LiDAR system – which consists of a laser, scanner and optics, a specialized GPS system and photodetector and receiver electronics – is attached to an aircraft which flies over the site to be surveyed.
Light from a laser is fired rapidly at the ground from the plane or helicopter: the beam scans from side to side as the aircraft flies over the survey site. The laser light is reflected back to a sensor, which measures the time taken for the pulse to return before calculating the distance to the target. Variances in the laser return times and wavelengths can then be utilized to create a detailed 3D map.
The LiDAR system measures between 20,000 and 100,000 points per second to build an accurate model of the ground and the features upon it. The technique can be used to visualize objects in woodlands as the laser is able to penetrate gaps in the woodland canopy, thus recording the ground surface under the trees to expose otherwise unseen features.
One area where this technique has had a significant impact is in New England, particularly Connecticut and Massachusetts – areas critical to the early European settlers in North America. The area has become heavily forested since much of it was abandoned in the 1950s, but LiDAR has revealed that during the 1700s – colonial times – the area was covered in roads, farm walls, and homesteads. The technique has allowed the unearthing of areas not included in historical records and for archaeologists to find features they never knew existed.
The Future of LiDAR
The future of LiDAR in archaeology is as bright as the laser light it uses; archaeologists and researchers are only just beginning to understand how the technique can be used to unlock the secrets of ancient civilizations and improve our knowledge of the past. LiDAR is revealing what was once thought to be lost, and improvements in the technique will enable us to learn more – LiDAR is a significant tool in the toolbox of archaeologists around the world.
Sources and Further Reading
This article was updated on the 12th December, 2019.
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