Archaeological surveys: How drones became an essential tool for historians

The following guest post about using drones for archaeological surveys was written by Peter Leslie, Director of Skykam. Skykam is a drone inspection company based in Edinburgh, Scotland.  

One of the most exciting archaeological developments in recent years: using drones for archaeological surveys. Drones allow archaeologists to cover more ground than they could on foot, and — because they can take pictures from all angles — their data is accurate and comprehensive.

In 2018, the national trust for Scotland adopted drones to document archaeology on a set of remote Scottish Islands using a fixed-wing drone that flew 250 miles over five days. The drone took 4,000 ultra-high-resolution photos and 420 million data points, a massive data set that was considered collected at record speed.

Prior to drones, projects like these relied on costly and time-consuming traditional aerial photography methods or ground operations. A helicopter can cost thousands of dollars per hour to hire. Meanwhile, drones can fly much closer to the ground, generating more detailed images and more accurate 3D models.

How drones are used for archaeological surveys

Drones have enabled archaeologists and historians to collect data faster than ever before (in general, groundwork surveying time can be reduced from 2-3 weeks to 1-4 days). Drones are now used in archaeology for tasks including:

• Documenting and recording new discoveries
• Assisting in planning for future dig sites
• Assessing damage to ancient sites from natural disasters or human activity
• Monitoring illegal excavation and looting of artefacts 
• Assisting in digital reconstruction of ancient sites

Since 2019, Skykam, an Edinburgh-based drone service, has been operating drones to generate accurate 3D models of historical Scottish landmarks including Glamis Castle, the Red Castle, and Caterthuns. The business has six drones in its arsenal, including a DJI Matric 300 RTK. 

In archaeology, typically either photogrammetry or Lidar methods are used to analyze sites.

Photogrammetry mapping ancient sites can help archaeologists understand a site’s true condition

Prior to drones, archaeological mapping required time-consuming ground-level observations, low-quality satellite images, or expensive helicopter photography.

With drones, creating either 3D models or flat maps is systematic and efficient through photogrammetry. Skykam typically uses a DJI Mavic 2 Pro for its photogrammetry work in a process that takes 5-10 minutes to fly over most properties. From there, Pix4D software ties it together. Although photogrammetry claims 2.9 cm accuracy to the original object, a higher level of precision may be required for archaeological research.

Lidar mapping can provide even greater detail (at a greater cost)

Lidar is a surveying technology that measures distances with lasers, used to build industrial-level accurate maps and models of an area with a better accuracy rate than photogrammetry. This method is regarded as one of the most precise methods of doing surveys. Among its advantages for archaeologists:

• Providing a high level of detail.
• Creating 3D models.
• Piloting a lidar drone does not need any additional piloting skills or a licence .beyond standard drone flying, though understanding of lidar itself is critical.
• Lidar is also unaffected by weather circumstances such as cloud cover and changing lighting conditions, both of which can significantly hamper airborne data collecting with photogrammetry.
• It can be used to map even the most minute characteristics of a given area (For example, surveyors can even remove foliage and trees from the models to get a clear glimpse of what lies beneath).
  

However, lidar mapping is far more expensive than normal drone surveying. Lidar drones such as the DJI Matrice 300 RTK with a lidar camera cost $35,000 (though, Lidar sensor costs vary depending on the type and quality). The family of mdLiDAR3000 integrated solutions boasts an accuracy of 1-2 cm in its mapping.

In 2019 the researchers at Crow Canyon Archaeology Centre mapped an ancient site in South Colorado to create an ultra-high resolution landscape model. Since the site was located in difficult terrain including a treacherous canyon, researchers used Lidar-equipped drones.

During the survey, almost 3.2 billion data points were recorded using LidarViewer Pro in a process that digitally removed nearly all vegetation, allowing archaeologists to examine the structures in greater detail.

“This survey approach illustrated how the tool could be used to record undocumented sites with unprecedented precision,” said Mark D. Varien, Executive Vice President of the Research Institute at Crow Canyon Archaeological Centre. “It removed the need for a painstaking ground survey and the speed of delivery of such detailed results is impressive. It has accelerated our understanding – the results indicate the pueblo was more extensive than we had previously imagined. We are now able to concentrate our future work in a small finite area – to study the new found kivas in more detail.”

Evaluating structural conditions can benefit historical preservation

Additionally, drones can help experts to assess any damage or deterioration in historical structures including castles, temples and pyramids, which is crucial for determining the best steps for preservation and restoration. 

For example, the Getty Conservation Institute (GCI) used drones to monitor the condition of Syria’s ancient city of Palmyra, capturing images that then generated 3D models used for management, conservation, and research — assisting in conservation planning of the ancient city.

By evaluating the condition of a structure, archaeologists and historians can determine the best course of action for preservation.  In the case of Skycam’s flight around the Red Castle, archaeologists learned the site had significantly more sandstone erosion than originally thought. In that case, preservationists could fence off that area as they plan future restoration. 

The bottom line: Archaeological surveys and drones

Drone technology is being adopted rapidly among archaeologists. From mapping out ancient sites to creating 3D models, drone use in archaeological surveys has proven an essential tool for uncover lost treasures or structures, or preserving the ones we know we have.

Peter Leslie is the Director of Skykam. Started in 2019, Skykam is a Scotland-based drone inspection service and aerial photography company. Skykam is fully insured and compliant with Scottish Drone Laws. 

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