CITY LIVING A plaza in Caracol, a Maya city in Belize. Jungles surrounding it were penetrated using a new method, lidar.
By JOHN NOBLE WILFORD For the New York Times
For a quarter of a century, two archaeologists and their team slogged through wild tropical vegetation to investigate and map the remains of one of the largest Maya cities, in Central America. Slow, sweaty hacking with machetes seemed to be the only way to discover the breadth of an ancient urban landscape now hidden beneath a dense forest canopy.
Even the new remote-sensing technologies, so effective in recent decades at surveying other archaeological sites, were no help. Imaging radar and multispectral surveys by air and from space could not "see" through the trees.
Then, in the dry spring season a year ago, the husband-and-wife team of Arlen F. Chase and Diane Z. Chase tried a new approach using airborne laser signals that penetrate the jungle cover and are reflected from the ground below. They yielded 3-D images of the site of ancient Caracol, in Belize, one of the great cities of the Maya lowlands.
In only four days, a twin-engine aircraft equipped with an advanced version of lidar (light detection and ranging) flew back and forth over the jungle and collected data surpassing the results of two and a half decades of on-the-ground mapping, the archaeologists said. After three weeks of laboratory processing, the almost 10 hours of laser measurements showed topographic detail over an area of 80 square miles, notably settlement patterns of grand architecture and modest house mounds, roadways and agricultural terraces.
"We were blown away," Dr. Diane Chase said recently, recalling their first examination of the images. "We believe that lidar will help transform Maya archaeology much in the same way that radiocarbon dating did in the 1950s and interpretations of Maya hieroglyphs did in the 1980s and '90s."
The Chases, who are professors of anthropology at the University of Central Florida in Orlando, had determined from earlier surveys that Caracol extended over a wide area in its heyday, between A.D. 550 and 900. From a ceremonial center of palaces and broad plazas, it stretched out to industrial zones and poor neighborhoods and beyond to suburbs of substantial houses, markets and terraced fields and reservoirs.
This picture of urban sprawl led the Chases to estimate the city's population at its peak at more than 115,000. But some archaeologists doubted the evidence warranted such expansive interpretations.
"Now we have a totality of data and see the entire landscape," Dr. Arlen Chase said of the laser findings. "We know the size of the site, its boundaries, and this confirms our population estimates, and we see all this terracing and begin to know how the people fed themselves."
The Caracol survey was the first application of the advanced laser technology on such a large archaeological site. Several journal articles describe the use of lidar in the vicinity of Stonehenge in England and elsewhere at an Iron Age fort and American plantation sites. Only last year, Sarah H. Parcak of the University of Alabama at Birmingham predicted, "Lidar imagery will have much to offer the archaeology of the rain forest regions."
The Chases said they had been unaware of Dr. Parcak's assessment, in her book "Satellite Remote Sensing for Archaeology" (Routledge, 2009), when they embarked on the Caracol survey. They acted on the recommendation of a Central Florida colleague, John F. Weishampel, a biologist who had for years used airborne laser sensors to study forests and other vegetation.
Dr. Weishampel arranged for the primary financing of the project from the little-known space archaeology program of the National Aeronautics and Space Administration. The flights were conducted by the National Science Foundation's National Center for Airborne Laser Mapping, operated by the University of Florida and the University of California, Berkeley.
Other archaeologists, who were not involved in the research but were familiar with the results, said the technology should be a boon to explorations, especially ones in the tropics, with its heavily overgrown vegetation, including pre-Columbian sites throughout Mexico and Central America. But they emphasized that it would not obviate the need to follow up with traditional mapping to establish "ground truth."
Jeremy A. Sabloff, a former director of the University of Pennsylvania Museum of Archaeology and Anthropology and now president of the Santa Fe Institute in New Mexico, said he wished he had had lidar when he was working in the Maya ruins at Sayil, in Mexico.
The new laser technology, Dr. Sabloff said, "would definitely have speeded up our mapping, given us more details and would have enabled us to refine our research questions and hypotheses much earlier in our field program than was possible in the 1980s."
At first, Payson D. Sheets, a University of Colorado archaeologist, was not impressed with lidar. A NASA aircraft tested the laser system over his research area in Costa Rica, he said, "but when I saw it recorded the water in a lake sloping at 14 degrees, I did not use it again."
Now, after examining the imagery from Caracol, Dr. Sheets said he planned to try lidar, with its improved technology, again. "I was stunned by the crisp precision and fine-grained resolution," he said.
"Finally, we have a nondestructive and rapid means of documenting the present ground surface through heavy vegetation cover," Dr. Sheets said, adding, "One can easily imagine, given the Caracol success, how important this would be in Southeast Asia, with the Khmer civilization at places like Angkor Wat."
In recent reports at meetings of Mayanists and in interviews, the Chases noted that previous remote-sensing techniques focused more on the discovery of archaeological sites than on the detailed imaging of on-ground remains. The sensors could not see through much of the forest to resolve just how big the ancient cities had been. As a consequence, archaeologists may have underestimated the scope of Mayan accomplishments.
For the Caracol survey, the aircraft flew less than a half-mile above the terrain at the end of the dry season, when foliage is less dense. The Airborne Laser Terrain Mapper, as the specific advanced system is named, issued steady light pulses along 62 north-south flight lines and 60 east-west lines. This reached to what appeared to be the fringes of the city's outer suburbs and most agricultural terraces, showing that the urban expanse encompassed at least 70 square miles.
Not all the laser pulses transmitted from the aircraft made it to the surface. Some were reflected by the tops of trees. But enough reached the ground and were reflected back to the airborne instruments. These signals, measured and triangulated by GPS receivers and processed by computers, produced images of the surface contours. This revealed distinct patterns of building ruins, causeways and other human modifications of the landscape.
The years the Chases spent on traditional explorations at Caracol laid the foundation for confirming the effectiveness of the laser technology. Details in the new images clearly matched their maps of known structures and cultural features, the archaeologists said. When the teams returned to the field, they used the laser images to find several causeways, terraced fields and many ruins they had overlooked.
The Chases said the new research demonstrates how a large, sustainable agricultural society could thrive in a tropical environment and thus account for the robust Maya civilization in its classic period from A.D. 250 to 900.
"This will revolutionize the way we do settlement studies of the Maya," Dr. Arlen Chase said on returning from this spring's research at Caracol.
Lidar is not expected to have universal application. Dr. Sheets said that, for example, it would not be useful at his pre-Columbian site at Cerén, in El Salvador. The ancient village and what were its surrounding manioc fields are buried under many feet of volcanic ash, beyond laser detection.
Other modern technologies, including radar and satellite imaging, are already proving effective in the land beyond the temples at Angkor, in Cambodia, and in surveys of the Nile delta and ancient irrigation systems in Iraq.
Laser signals breaking through jungle cover are only the newest form of remote sensing in the pursuit of knowledge of past cultures, which began in earnest about a century ago with the advent of aerial photography. Charles Lindbergh drew attention to its application in archaeology with picture-taking flights over unexplored Pueblo cliff dwellings in the American Southwest.
NASA recently stepped up its promotion of technologies developed for broad surveys of Earth and other planets to be used in archaeological research. Starting with a few preliminary tests over the years, the agency has now established a formal program for financing archaeological remote-sensing projects by air and space.
"We're not looking for monoliths on the Moon," joked Craig Dobson, manager of the NASA space archaeology program.
Every two years, Dr. Dobson said, NASA issues several three-year grants for the use of remote sensing at ancient sites. In addition to the Caracol tests, the program is supporting two other Maya research efforts, surveys of settlement patterns in North Africa and Mexico and reconnaissance of ancient ruins in the Mekong River Valley and around Angkor Wat.
Nothing like a latter-day Apollo project, of course, but the archaeology program is growing, Dr. Dobson said, and will soon double in size, to an annual budget of $1 million.
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New structures ‘unearthed’ at Belize’s Caracol Mayan Ruin
The ruins of Caracol are located in the Vaca Plateau of the Cayo District and recent studies performed by NASA have unearthed thousands of new structures using their most advanced technology. Utilizing NASA’s laser tools, researchers have discovered and illustrated in a 3D form, the complex urban centers built at the ancient Maya City of Caracol.
In a press briefing on Tuesday, May 11th, a NASA based group revealed information - which normally would take 25 years to collect – and was done over a span of 4 days gathered by using a technique called LiDar (light Detection and Ranging). Airborne LiDAR made research significantly easier, and faster, allowing researchers to see 'beyond the rainforest'. Laser beams emitted from a plane were able to penetrate the thick canopy that covers the site to reach sensors on the ground. The laser survey then produced images of the ancient settlement and its surroundings, covering a 200 square kilometre radius in just four days. “It is very exciting,” said Arlen Chase, Anthropology Professor at the University of Central Florida, where the data is being analyzed. “The images not only reveal topography and built features, but also demonstrate the integration of residential groups, monumental architecture, roadways and agricultural terraces, vividly illustrating a complete communication, transportation and subsistence system.” This breakthrough and results of the LiDAR mapping project in Caracol are significant. A total of eleven new causeways, five new causeway termini, tens of thousands of agricultural terraces and many hidden caves were located.
The new developments have prompted Nasa’s researchers to recreate the Caracol landscape in 3D model so as to better understand the Maya Civilization in an effort to discover clues as to what may have happened to the maya empire in that era.
Currently in the state of excavation and restoration Caracol is the largest known Maya center in Belize. The largest pyramid in Caracol, "Canaa" (Sky Place), rises 140 feet high, and it is the tallest manmade structure in all of Belize. Since Caracol is located in the Chiquibul Rain Forest, there is a plethora of flora and fauna to enhance the true beauty of this magnificent Maya center. Caracol is an enormous ceremonial center, perhaps the largest site in Belize.
Laser Mapping Helps Archaeologists and City Planners LiDAR technology can be used to predict natural disasters
By Marlene Cimons, National Science Foundation
Caracol, the site of an ancient Mayan city, is the largest archeological site in Belize, and has been a focus of scientific exploration for decades. Until recently, however, the only way researchers could uncover its wonders was to slowly and laboriously hack their way through the dense jungle overgrowth with machetes and other tools.
But nearly three years ago, researchers tried a new approach, flying over the area with laser technology that can penetrate through the tiniest openings in the rainforest canopy, for the first time allowing archaeologists an unencumbered--and unprecedented--three dimensional view of a vast expanse of this early urban civilization.
"The archaeologists were able to learn things they hadn't known before, for example, that the settlement was much larger than they had seen earlier, with the remains of previously undiscovered structures and more extensive agricultural fields," says William Carter, senior engineer for the National Center For Airborne Laser Mapping (NCALM), which has made major contributions to the development and application of the technology during the past decade.
"Essentially, we can remove the vegetation from the terrain so you can see what's below it," he adds. "It enables scientists and others to see what the actual bare earth is beneath the vegetation. In this case, it helps provide information about a past civilization."
Airborne light detection and ranging (LiDAR) technology, which combines sophisticated laser surveying instruments and GPS, allows scientists to create bare earth maps of thousands of square kilometers with decimeter resolution in a matter of days, regardless of the extent of forests or other vegetation.
More recently, the center also purchased a high pulse rate 'green' laser (which refers to the color of its light) LiDAR unit with the ability to penetrate shallow water.
In addition to its applications in the field of archaeology, information generated by their work holds benefits in predicting as well as coping with the aftermath of landslides, earthquakes, river and coastal flooding, and beach erosion, among other things.
"The data will help in planning for, responding to, and mitigating the impacts of disasters, both from natural and human causes," Carter says.
Ultimately, the researchers hope to develop ways to transfer the laser technology to small unpiloted aerial vehicles, or UAVs. Although they are not yet available, they could prove especially valuable during or after future natural disasters.
"We could launch one immediately after an earthquake, or during a hurricane, for example, when it still isn't safe for a pilot to be up there," Carter says. "Instead of trying to locate an airport to operate from in an area struggling to recover from a disaster, we could send out one of these UAVs. With no need for local support, we could collect the data, and send it back in near real time, so we could analyze it and provide information to responders on the most heavily damaged areas."
The center traces its origins to a University of Florida research group formed by Carter and Ramesh Shrestha, a civil and environmental engineer during the latter half of the 1990s. The actual center began in 2002, in collaboration with Bill Dietrich, a professor in the earth and planetary science department at the University of California at Berkeley. Today, the NCALM operations center is located at the University of Houston, where Shrestha leads a geo-sensing systems engineering program and serves as center director.
The National Science Foundation funds the center with about $1 million annually, as well as providing additional financial resources--sometimes more than $1 million a year--to support research projects using the technology.
For example, "using data we collected, a researcher discovered that a landslide blocked the Eel river, in northern California, 22,500 years ago, forming a lake and blocking the trout breeding runs up to the higher areas, apparently resulting in two different types of trout interbreeding to create a new breed peculiar to that river today," Carter says.
The state-of-the-art laser instruments have, in the past, produced updated and accurate maps of potential flood zones in Florida's Pinellas County, resulting in an estimated $25 million of savings annually in flood insurance costs. More recently, the technology mapped all the major fault lines in California, a template that will serve as a baseline for recording changes that occur after future earthquakes.
The researchers also mapped Ground Zero in New York to help workers identify entry routes for heavy equipment, find the best locations to erect and operate large cranes, select areas to dump waste, and identify damage to structures other than the Twin Towers.
In coastal areas, "mapping beaches after storms tells government officials where and how much sand has been lost, information that has important implications for the tourist business and the local economy," Carter says. "We map forests to determine the fuel content before fires, and after, to determine the extent of the damage, and to identify areas of possible future erosion and landslides associated with the loss of forests."
Center scientists also map coastal wetlands to determine the extent of the damage caused by oil spills, and streams, in order to locate fish breeding grounds and obstructions, such as unapproved dams, that block the runs of fish up-stream in breeding seasons. They also have conducted work for the citrus industry to identify areas of blight.
Flying above ground, the laser shoots pulses of light - 100,000 per second and about a dozen or so hits per square meter--many of them able to make their way through the smallest of openings in the forest canopy.
"During presentations we make, we generally find that people are most amazed and react openly to seeing an area covered with a forest, and then seeing the same area after we have filtered out the vegetation," Carter says. "They suddenly can see things such as landslides, fault lines, archaeological sites and streams that are otherwise hidden below the forest."
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.
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.