Crucially, some of the laser light is also able to penetrate vegetation. So, in the case of areas covered in a forest canopy, such as in Caracol, some of the pulses will hit the top of tree canopy, some the middle, others the forest floor. Software can then be used to remove the points above the ground, according to University of Alabama archaeologist Dr Sarah Parcak, who is not part of the Chase team but has used Lidar at other sites. This leaves a detailed “digital elevation” model of the hidden forest floor with the ability to pick out features as small as 20cm across.
“It is an amazing tool,” says Parcak. “You cannot use anything else in areas such as Central America to visualize Mayan ruins in a clear way.
The measurements are exact enough that the Chases were able to overlay the new map onto the painstakingly, hand-created maps of their site with an unexpected level of exactitude. But what really astounded them was the amount of detail they had never seen before.
Previously, they had mapped around 3.5 sq km of agricultural terraces on the site. The Lidar revealed more than 150 sq km more. In addition, it revealed thousands of new buildings arranged around squares, 11 new waterways, more than 60 caves as well as clues that suggest there could be up to 1400 water reservoirs on the site. All in all, one fly-over had radically increased the size of the ancient capital. Overnight it changed archaeologists’ perception of the site from a rarely-inhabited ceremonial center to a bustling city with a complex system of agriculture to support it.
It is tempting put characterize this kind of revelation as a one-off success. But, Lidar’s success is not confined to Caracol. Further north, a team from Colorado State University has also used the technique in the Patzcuaro Basin, a region in the west of Mexico. The area was the centre of the Purepecha Empire – contemporaries of the Mayan and Aztec civilizations that have never caught public attention. They can be thought of as the people who stopped the advance of the Aztecs into San Diego and were also famous for their intricate metal work.
In 2007, Colorado State University professor Chris Fisher began investigating the area. That year, he and his team found some impressive treasures including an imperial treasury building, where the leaders kept their stores of hummingbird and macaw feathers, the dominant currency. A year later, equipped with handheld GPS units his team spent three months on foot mapping the area in search of other treats. But, what they uncovered surprised even them.
At a spot in an ancient road that previous surveys had marked down as little more than a widening of the carriageway, the team began to uncover evidence of buildings. Lots of buildings. Over three months, the team of between 12 and 16 people unearthed evidence for more than 1,400 buildings. It seemed that the wide spot in the road was in reality a surprisingly large pre-Hispanic capital.
But it wasn’t until last year that Fisher and his team would know just how big. Equipped with Lidar the team flew over that spot recording 3,000 buildings in half the time it had taken them with ground surveys.
“When Lidar was first used at Angamuco we had no idea how large the area was that included buildings and structures, if it was even a city,” team member Professor Steve Leisz told the BBC. Perhaps more surprisingly the team also found a ball court for a Meso American game called pok-ta-pok, and pyramids, including one that Fisher had walked within 10m of the previous year. “That was a complete surprise,” said Leisz.