Archeology from space — discovering history from a few hundred kilometres up

Originally published on September 14, 2019.

Sarah Parcak can see things from space that the rest of us can't see even when we're standing on top of them. Using eyes in the sky, she's found buried and invisible Roman ruins, Egyptian cities, and even identified a potential Viking site in Newfoundland.  

Parcak is part of a new breed of archeologists who've been using Earth-observing satellites to hunt for ancient archeological sites. These satellites can take images in extreme wavelengths of light, so she can get a new perspective not just from above, but in light waves beyond what human eyes can perceive. 

She compares this to a space-based CAT scan. "You're essentially enhancing these virtually invisible subtle differences and really making the features pop out so that you can detect them."

Parcak tells the story of the new field nicknamed 'space archeology,' and more formally known as satellite remote sensing, in her new book Archaeology from Space — How the Future Shapes our Past.

The history of space archeology

She told Quirks & Quarks host Bob McDonald that the roots of the field lie in the space race and the cold war.

Starting in the 1950s, the US developed and launched spy satellites that were capable of taking high resolution photographs of the Earth — or at least parts of it. "They didn't just take pictures of Russia," said Parcak, "They ended up taking pictures of the Middle East, North Africa and so many other places."

When these images were declassified in the 1990s, they became available to archeologists. "We could essentially order this really amazing imagery, and using it you can see all these amazing sites that have to a large extent disappeared today with urbanisation."

Parcak has used spy satellite images to find a temple enclosure dating back 2300 years at Tell Tabilla, a site in Egypt. Spy satellite technology also foreshadowed the development of non-military earth-observing satellites, which take pictures in different parts of the light spectrum. That's the technology she largely uses today.

Seeing the invisible

These images can reveal long-buried sites invisible to the naked eye. One technique she's used looking for Roman ruins in Italy involves looking for the optical signature of plant growth that can be affected by buried buildings. 

"Roots of plants grow down and they hit the rock that forms the foundation of the archeological feature," said Parcak. This results in slightly less growth over stone ruins. This is invisible to the eye, but satellites can observe in the near infrared part of the light spectrum, which is sensitive to the chlorophyll in plants.

"Using satellite imagery, you can make this invisible wavelength appear then all of a sudden, you have this less healthy vegetation forming a perfect outline of something that matches a Roman villa."

Mapping an Egyptian site from Indiana Jones 

A few years ago. Parcak was recruited to apply similar techniques to search for ancient Viking settlements on the east coast of Canada. 

"We did the first large scale systematic satellite survey and eventually ended up finding something that looked like it could be a potential Viking or Norse feature."

Unfortunately, excavations at the site in southwest Newfoundland called Point Rosee produced no firm evidence of Viking occupation. Nevertheless, she thinks it'll stimulate the search for more Viking sites that could be out there.

More productive was her work in mapping the ancient city of Tanis in Egypt. On film, Tanis is famous as the site where Indiana Jones discovered the lost 'Ark of the Covenant.' In real life, it's an important archeological site preserving a city that was the capital of ancient Egypt 3000 years ago.

Archeologists have been excavating individual buildings in Tanis since the early 20th century, but its full extent had not been known.

"The main settlement of Tanis had never before been mapped. And that's what we saw from the satellite imagery," said Parcak."Multiple structures, potential palaces and city streets."

Aerial Laser surveys uncovering Mayan sites 

In her book, Parcak also describes work done by colleagues using aerial laser surveys that are revolutionizing Central American archeology. LIDAR, or light detection and ranging technology, has been used to great effect on heavily overgrown Mayan sites in Guatemala.

The LIDAR surveys can be used to virtually strip away the jungle overgrowth, revealing hidden ruins below, said Parcak.

"They found tens of thousands of previously unknown, undiscovered, Mayan features and sites and they've allowed us to get this incredible picture of the entire Mayan world. It's totally revolutionized Mayan archeology and told us that possibly millions of people live there."

Parcak says that this kind of archeology may seem different from the search for tombs and treasures familiar to us from fiction.Satellites can't find mummies and jewelry, but can reveal more important things about history.

"That's why satellite imagery is so powerful. It allows us to pull back and see things at a big scale and understand relationships between archeological sites and landscapes and really ask better questions about how past peoples lived."

Produced and written by Jim Lebans