Lasers map mysterious Iron Age passageways in Scotland

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February 2022 Graeme Cavers and his team of archaeologists set out to find a mysterious underground passage called the basement. There are about 500 such Iron Age structures scattered throughout the Scottish Highlands, but no one knows what they were built for, and no one has ever found a single one intact.

“Perhaps they were intended to store, for example, grain in airtight pots or dairy products such as cheese,” says Matt Ritchie, resident archaeologist at Forestry and Lands Scotland. “Perhaps they were needed for security, for the safety of valuables or the safety of slaves or hostages. Or perhaps they were intended for ceremonial purposes, for domestic rituals, like a medieval shrine or private chapel.”

Surveying the area can help shed light on the condition and structure of the basements, but using traditional methods they can take at least a week, says Cavers, whose AOC Archeology company was brought in by Ritchie to help map Cracknie Souterrain in the Scottish forest of Borghi.

Manual measurements with a device called theodolite, which is difficult to use in dark, cramped tunnels, have been replaced by laser scanners, which have improved markedly over the past few decades. “They used to connect to an external laptop,” Keyvers says. “Data could only be written as fast as this connection. This was done over an ethernet cable, so it was relatively fast. But even then, the first laptops that I used with a scanner had 2 gigabytes of RAM. This was the top of the range. And a laptop cost a lot of money in those days.”

Since then, the technology has come a long way. After sneaking into the Cracknie Souterrain through a 50cm hole in the ground, Speivers was handed a gray shoebox-sized device: a Leica BLK360 laser scanner.

The cavers set up the device on a tripod in a 1-meter-high wet passage, adjusted a few settings, and hit “scan.” He turned around and began firing lasers at the basement walls 10,000 times per second. Keyvers and his team can now take millions of measurements in less than an hour without lifting a finger – Crackney has taken 50 million measurements in just a few hours. “To do the same thing that we did with the theodolite, you would have to be there for a long time,” says Keyvers.

Collecting large datasets is a challenge in itself. “Today we are coming back with half a terabyte of data,” he says. “And we could do a couple hundred projects a year. It becomes very difficult to manage from an IT perspective. And obviously we are archaeologists; we must create eternal archives for the long term.”

However, the data pays off. Cavers once had to paint or photograph the basement from a dark passage, which would have defied his persistence without natural light. He now uses software – Trimble RealWorks, NUBIGON and Blender – to create accessible 3D multi-color “point cloud” models.

Team members can then look at the models from any angle they like and measure the distances between any two objects, as well as change colors according to variables such as height and density. This means that archaeologists like Ritchie can tell people about archaeological sites without visiting them.

“[Cracknie] very far away,” Richie says. “It’s far from established hiking trails and relatively difficult to access.” This means it is not well suited for tours or educational panels, but the 3D model can be viewed from anywhere. Richie could even print out a scale model and put it in a museum. This technology is making Britain’s cultural heritage more accessible and could one day help archaeologists like Ritchie unravel the mystery of Scottish underground.

This article was originally published in the January/February 2023 issue of WIRED UK magazine.

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