For the best part of 25 years, archaeologists Arlen and Diane Chase slogged through the thick undergrowth in the west of Belize in search of an ancient city whose details had been lost to the passage of time and the decay of the jungle.
The going was tough, often requiring a machete to clear a path through the dense vines and creepers that blocked their way. Over time, their perseverance paid off as their hand-drawn maps began to reveal long-forgotten parts of the massive Mayan city of Caracol.
But the more the pair found, the more they realized the extent of what remained uncovered. It would take several lifetimes, they figured, to reveal the true extent of Caracol.
Then, in 2008, they got talking to a biologist colleague at the University of Central Florida where they worked. For years, he had been using airborne laser sensors known as Lidar (Light Detection And Ranging) to map and study forests and other vegetation. He suggested they give it a go.
So, in 2009, the pair packed away their machetes and hiking boots and commissioned the National Center for Airborne Laser Mapping (NCALM) to fly a twin-engine plane backwards and forwards over the tree-tops firing pulses of laser light at the ground below. A few weeks later, the pair got their first look at the results.
“I was completely astounded,” says Arlen Chase. “We had not expected the clarity that we saw in the imagery.”
“I am pretty sure we uttered some expletives,” Diane adds politely.
In less than a week, the team collected more data than they had in a quarter of century of hacking their way through the jungle. Analysis revealed a host of previously undiscovered features, including several in areas that they had previously mapped on foot. It was a revelation.
Now, archaeologists around the world are beginning to embrace the same technique, flying aircraft over everything from Stonehenge to patches of scrub, in search of hidden treasures. The findings are already beginning to challenge conventional theories and change our view of the size and extent of ancient civilizations. But, while some say we are on the cusp of a new golden age of discovery, it is also beginning to throw up difficult questions about the disappearance of ancient civilizations.
Using technology in archaeological expeditions is nothing new. Techniques similar to those used in the offshore oil industry have been used for years by archaeologists on the ground to spot buried structures. Increasingly, archaeologists are using satellite photography with success, for example, increasing the number of structures in the Nile valley including 17 new pyramids. In August, two more were found using images from Google Earth. Radar has even been used, famously uncovering vast new areas of the vast Cambodian temple complex Angkor Wat.
But Lidar seems to offer several advantages. It is quick, relatively cheap and can be used to map large areas very quickly, particularly those covered in dense vegetation.
The technology has been used in a variety of ways over the last two decades, from gauging distances between cars in adaptive cruise control to mapping forest canopies and detecting the amount of aerosols in the atmosphere. But, no matter what the use, most modern Lidar systems are essentially the same. All shoot thousands of pulses of laser light and then use sensors to detect any reflections. By measuring the time it takes between sending out a pulse and measuring the light bouncing back, software can begin to build up a picture of the machine’s surroundings. Using it in combination with GPS and other location technologies, it allows very accurate 3D maps to be built.