Laser vision reveals hidden worlds

Mapping technology lets researchers see what the naked eye cannot

Some of the central pyramids of ancient Caracol in Belize. Laser mapping showed that at its peak, this Mayan metropolis sprawled over an area the size of present-day Washington, D.C.

In the ancient Maya city of Caracol, map-making can be treacherous. Jungles shroud this site in the Central American nation of Belize. Dense shrubs stand taller than a person’s head. They hide ruins that otherwise would be obvious. To reveal the city, archeologists must hack through the growth, using sharp blades called machetes. They step carefully to avoid critters like the fer-de-lance, a common viper with an often-fatal bite.

Arlen and Diane Chase know these hazards well. These archeologists work at the University of Central Florida in Orlando. For three decades, the husband-and-wife team (who cut their wedding cake with a machete) also have patiently studied Caracol. Season by season, they and their team — and later, their children — have hacked and mapped, hacked and mapped.

Then, in April 2009, everything changed. That’s when lidar came to Caracol. Lidar stands for “light detection and ranging.” It’s a method of using lasers to create a map. And it revealed this part of the world in a whole new light.

For five days, a small Cessna airplane buzzed over Caracol and the surrounding region. Onboard, a device fired laser pulses at the ground. And not just a few: This machine sent billions of pulses streaming into the jungle. Some laser pulses vanished in the heavy tree cover. Many others bounced off leaves and returned to the plane. Still others reflected off of the ground or hidden stone structures. The lidar device recorded how long it took the echo of each pulse to return. The device used those bounce times to compute how far the light had traveled. In total, it recorded more than 4 billion measurements of the jungle terrain.

Back on the ground, computer programs turned those data into a detailed map of the site. The laser pulses revealed the contours of temples and other buildings, roadways and even terraced fields. It was as if lidar had peeled back the jungle to reveal much more of Caracol than anyone had seen since the Maya city went into decline more than 1,000 years ago.

Arlen Chase said that all at once he could “see” the jungle-covered ruins he and Diane had painstakingly charted over the decades. This map also turned up many other hidden archeological features. “I couldn’t stop looking at it,” he says. “It was mind-boggling.”

From underground to outer space

Laser-built maps can reveal ruins hidden for centuries. And not only in Belize. Elsewhere around the world, lidar projects have been uncovering other hidden treasures. These observations are inspiring scientists to question what they thought they knew about how ancient civilizations lived.

Nor is archeology the only field getting a boost from lasers. Scientists use lidar anywhere a map might be useful, from high above Earth to deep below. Some experts have been charting clouds and gases in the atmosphere with lidar. Others have probed deep dark caves and the changing shapes of coastlines. The technology even has been used to map the surfaces of Mars, Mercury and the moon.

“There’s no other way to collect this kind of data,” says Andrew Fountain. A geologist at Portland State University in Oregon, Fountain has used lidar to map changes in ice-free deserts in Antarctica.

The strategy behind lidar is simple. Beam out a bunch of light pulses and record those that bounce back. The same idea underlies other sensing technologies, such as radar and sonar.

Radar devices emit invisible radio waves. Those waves that bounce back reveal the location or speed of distant objects. That is why police officers use radar guns to scout for speeders among passing cars.

Similarly, sonar devices emit sounds and listen for echoes. This method even works underwater, where sound travels farther than light or radio waves. Some animals have naturally developed a type of sonar. Both bats and dolphins can “see” in dim places by producing sounds and listening for echoes. This natural sonar is called echolocation.

In the 1970s, NASA missions used lidar to study Earth’s atmosphere. In the early 21st century, the precision of laser mapping increased and its costs dropped. Early lidar instruments fired 3,000 pulses per second of one color. Newer ones emit 900,000 pulses per second and use multiple colors. Different colors of laser light penetrate or reflect off of materials differently. So multiple lidar beams could capture more information. For example, multiple-beam data might show the types of trees and other plants in a forest.

Today, scientists can use these systems to explore hidden structures almost anywhere. At about the same time, global positioning systems, or GPS, have made it possible to link the laser maps to specific locations.

Expanding horizons

The Chases began their work at Caracol in 1985. That was long before lidar was an option. Back then, textbooks described this site as a small settlement that had played a minor role in Maya history. Gradually, the Chases started turning up hints that Caracol was much bigger than those textbooks had suggested. They found roadways leading away from the center of the ruins. They found an inscription, carved into rock, that told of the city’s history — and boasted of triumphs over powerful neighbors.

Year by year, the Chases and their team built a case that Caracol was once a powerful and important Maya capital.

“Hardly anybody believes it when they wander the countryside,” says Arlen Chase. “We had been telling our colleagues for years” that Caracol was much bigger than it looks. “But we couldn’t demonstrate it.”

The 2009 lidar project finally delivered the solid evidence that Caracol had been a sprawling metropolis. The Chases had initially estimated Caracol covered some 23 square kilometers (about 9 square miles). The lidar data suggested the city was far, far bigger — roughly 177 square kilometers (68.3 square miles). That is the size of Washington, D.C.

The researchers used lidar to map the terraced fields that fed the estimated 115,000 people who lived in Caracol. The maps also revealed roadways and reservoirs no one even knew had existed.

Ancient cities in the tropics

With lidar mapping, Caracol quickly morphed from a mid-size village to a major “city in the tropics,” says Arlen Chase. And before long, researchers elsewhere trained lidar on a host of other sites in Central America.

A 2013 study in Honduras spotted ruins that some speculate may be part of a legendary lost city known as La Ciudad Blanca. That year brought a second lidar survey of Caracol. It mapped more than 1,000 square kilometers (386 square miles), including much of the area surrounding the city. That survey shows that Caracol was even larger than the Chases had thought. The original city probably spilled over into what is today Guatemala.

Lidar technology is simply “eye-opening,” says John Weishampel. He’s an ecologist at the University of Central Florida who often works with the Chases. If you want to map a site like Caracol from the ground, he notes, “you’re talking decades.” But survey it from the air using lidar, he says, and the same things can be mapped with “probably two weeks of flight time and three weeks of [computer] processing.”

These Florida scientists are now analyzing the Caracol data for insights into the ancient Maya civilization. Arlen Chase says their latest map offers an even better sense of how the city fit within the larger Maya landscape. The Maya empire was one of the most advanced ancient civilizations in the Americas. At its peak about 1,400 years ago, its network of cities occupied parts or all of southern Mexico, Belize, El Salvador, Guatemala and Honduras.

Student Science

Caracol Altar 26 revisited

This is for tour guides or anyone that would like to know a little more details about alter 26 feel free to download and share the info. this was published by Mexicon

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