Seeing below from above: drones in archaeology

Historic England, a British public body that oversees historic building and monument conservation, has been using both fixed-wing and rotary drones for the past ten years. In that time it has discovered various use cases – not restricted to the UK – including:

  • Using mainly rotary drones for monitoring of sites – including roof and high-level wall top analysis; recording of excavated features; recording of still and video images
  • Capturing of interesting photos for marketing material and on-site displays
  • Site mapping, surveying and recording including for 3D surface models and  overlapping still imagery (in this use rotary drones are largely used to capture building information, and fixed wing drones capture landscapes).

We will look at some of these uses in more concrete examples below.

A-Maya-zing lidar

One interesting example of the power of technology in archaeology is the use of lidar (the visible-light equivalent of radar) to discover structures that would be practically unnoticeable on the ground. The recent example from the Mayan city of Tikal demonstrates the power of lidar – shooting out laser beams and building a map of what they hit through their deflection data. Lidar’s ability to ‘see through’ the thick blanket of vegetation in the jungles revealed that previous assumptions about the size of Mayan cities and its culture were grossly understated. Thomas Garrison from Ithaca College was part of a group of researchers which mapped an area of 800 square miles in the Petén region of Guatemala and it has overturned some long-held beliefs about the civilisation that flourished in the first millennium AD. The lidar images show that the Tikal area was home to two to three times the population than was previously inferred from ground-based research, with extensive housing and farms. The lidar survey revealed a total of around 60,000 previously unknown structures in the area. Also, the lidar has shown an extensive series of causeways connecting cities, and strong defensive walls and structures suggesting that warfare was more a part of everyday life than previously thought. The project will continue for three years and aims to map more than 5000 square miles of Guatemala’s lowlands.  

Wat a surprise

On the other side of the world in Cambodia lidar surveys were conducted on the Angkor Wat temple complex and wider area. They also revealed a larger than previously thought cluster of cities. Dr Peter Sharrock, a member of the board at London’s School of Oriental and African Studies (SOAS), said that what the survey revealed would have been the largest empire on earth in the 12th century. The survey showed that to the north of the Angkor temple complex there was a large city called Mahendraparvata on the mountain of Phenom Kulen which has since become overgrown with little remaining above-ground evidence. The lidar survey revealed that the city was as comparable in size to the modern-day Cambodian capital of Phnom Penh. Also uncovered was remains of complex water control systems such as dams and canals which could have provided the civilisation with the transport channels and water it needed to flourish. There are also some interesting geological structures reminiscent of mazes, with a snakelike structure winding to a central point. It has been hypothesised that these were landscaped gardens. Evidence of road links to another large city called Preah Khan Kompong Svay about 50km distant from Angkor also excited the researchers. They believe that this was a site that supplied iron to the city and was the largest temple complex/city built during the Angkor period at 22 square kilometres in size. It is postulated that as a social and economic centre it could even have been more important than Angkor.

Hot stuff

Lidar is one accessory that can be attached to a drone; another is thermal imaging cameras. Although these are more sensitive to interference from factors such as vegetation cover, time of day, and weather than lidar, in the right environment they excel. An example of the strength of thermal cameras and drones (aerial thermography) can be seen from a 2014 survey of a Pueblo Indian settlement at Blue J, New Mexico, where researchers were able to image detailed architectural plans of dozens of house compounds. The team also carried out aerial thermography surveys at a Shaker Village in New Hampshire, and it again revealed buildings and pathways invisible on the ground.

Even without sophisticated thermal cameras or lidar, drones with simple cameras can discover novel things. In Peru, previously unnoticed Nazca lines were discovered which were in plain sight all the time. The drone allowed them to go closer to the ground than traditional methods enabling the team to take photographs that showed faint geoglyphs of warriors.

On Minoans and massacres

It is not just in the detail that drones can capture that they show their advantages but also in their ability to be used easily, quickly and with high detail to record an excavation as it’s happening. In the Sissi Archaeological Project – a dig in Crete and Cyprus for relics of the Bronze Age Minoan civilisation – the introduction of a drone for aerial images provided advantages over methods that were previously used, such as kites and pole-photography. Those involved in the project say that the DJI drones they used allowed flights in most weather conditions, unlike the kite, and allowed them to fly as often as they liked. The level of control is another advantage, it allows the team to take high-resolution images – 1 cm/px for a 70x70m area – and video of features, trenches and the site. This can then be used to catalogue excavation progress, for publicity or educational purposes, or to produce stone-by-stone state plans for the architectural team.

In another example, Esri used its ArcGIS mapping and analytics system with drones to assist archaeologists in the field in Sweden. The Kalmar County Museum flew a drone over a 5th century fort on the island of Oland. The imagery from the drone was captured using Drone2Map for ArcGIS software also made by Esri to make a basemap and mark elevations. This allowed the team to see the outline of house structure within the fort. Excavations of the areas of interest were then documented daily using drones, which allowed the team to document their artefact finds. The team discovered that the inhabitants of the town were massacred about 1500 years ago. The museum has used the information collected by the ArcGIS system to create an interactive 3D map of the fort, which it has placed on its website.

Preservation

Of course, the preservation and surveying of ancient buildings is another area where drones can assist. British historic building conservation foundation National Trust (NT) used drones to survey Lindisfarne Castle, which is perched on a crag on the Northumbrian coast. The inaccessibility of areas of the site makes surveying with traditional methods a challenge. In a recent survey drones were used to carry out laser scanning and high-resolution digital photography of the castle. The drone also captured information on the area surrounding the site. The data was then used to map out structural moisture patterns from thermal images, and detail historical alterations in the building, and can be used to devise maintenance schedules and improve management of the site.

The examples above show that drones are a helpful tool for researchers, conservators and archaeologists, helping them uncover historic secrets, correct incorrect theories and preserve the past with increased efficiency and precision.  It waits to be seen how the relatively young field of drones in archaeology will grow as drones become increasingly capable and as technologies used with drones continue to evolve.

In fifteen years could a 6G-connected drone with a novel sensing technology reveal the location of the fabled city of Atlantis, or reveal ancient lost-civilisations on Mars? Probably not, but the future looks interesting.

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