Advantages of Lidar Scanning in Archeology
Lidar is the best choice for many different applications, including archaeology. The lidar wavelength is approximately half a micron(one micron equals 1/25,000 of an inch), much smaller than say radar wavelengths (which are in centimeters or decimeters).
For ground details big and small, lidar easily wins over radar.
Lidar was first used in the 1960s, shortly after lasers were invented. It works similarly to radar by calculating distance by measuring how long it takes for a bounced signal to return. Lidar, on the other hand, uses a light pulse rather than radio waves to send its signal.
European archaeologists were some of the first to use lidar in order to find hidden landscapes from different types of terrain back in the 1970s.
They were mostly just mapping old castles and fields at the time. It was all temperate-zone work, being all farmland. When it came to something like a rain forest lidar failed at penetrating the trees from flying above.
This was because lidar at the time worked at about 5,000 shots per second.
To be effective in areas with a dense forest canopy or even low-lying vegetation, the pulse rate needed to be increased. The first devices produced around 2,000 pulses per second, which were useless in the jungle since the majority of shots bounced off leaves and never reach the ground.
That problem has been solved thanks to many technological advances. Today’s archeologists can survey an area with a liar device that has pulse rates up to 600,000 shots per second.
The second characteristic that distinguishes modern lidar surveys is “stops per shot.” As it travels downward, each shot is scattered by leaves and other vegetation.
Lidar can count up to four “stops,” or obstructions, for each pulse. The ground is the fourth stop, if needed. The first image a lidar engineer views is called the “point cloud”, which looks like a foggy collection of every pulse and stop that the device has recorded from different heights.
A technician will use software to separate out everything except the last stop. The topography underneath the trees — the ground plan of an archaeological site — is what is revealed . By factoring in the variation of heights for objects on the ground, engineers are able to create maps that show contours and depict three dimensions.
Modern lidar technology uses lasers that are deployed from the air or handheld units. When these lasers hit an area, they will emit quick pulses of light. The amount of time it takes for the pulses to reflect back to the instrument is recorded, and each measurement is plotted with GPS. That data is used by computers to generate a 3D map of the region.
If you wanted to see what’s underground then using Ground Penetrating Radar would be the go to device to accomplish that.
Archeological Discoveries from Lidar
Below is just a small list of how using lidar in archeology has improved the speed of which archeological sites or entire ancient cities can mapped out:
Lidar technology has allowed archaeologists to discover nearly 500 new Mesoamerican sites that were built by the Maya and the Olmec in Mexico.
By using laser pulses connected to a GPS system, lidar was able to take topographical readings of a 30,000-square-mile area around eastern Tabasco and create a 3D map.
The findings were later studied by archaeologists, who discovered 478 probable ancient settlements dating from about 1400 B.C. to 1000 A.D., according to the report.
In just 10 hours, archaeologists were able to collect more topographical data using lidar than what their ground expeditions had yielded in almost 30 years.
The archaeologists surveyed about 7.7 square miles of the Caracol site between 1983 and 2000. The Chases mapped 77 square kilometers with lidar.
Cambodian Mahendraparvata Site
The ruins of Mahendraparvata, a 1,200-year-old city in the Cambodian jungle that was discovered using lidar, are another archeologists’ find. Australian archaeologist Damien Evans and his team found extensive, well-organized settlements over a 143 square mile area that the dense jungle canopy would have hidden from satellite imaging or ground surveys.
U.S. – New England
In the North America, lidar has helped researchers discover more about the land in New England.
New England is mostly covered in dense forests, making it difficult for archaeologists to understand what the region looked like during the early colonial period. However, lidar technology has allowed researchers to get a better idea of what life was like here centuries ago.
In 2009, Chris Fisher a Colorado State University archaeologist found out lidar and it’s many benefits. He was inspecting the ruins of Angamuco with a team of graduate students and assistants, walking slowly while keeping an eye out for shards of ceramic, old foundations or tombs.
He expected to find a very small village, but instead he discovered a large city of the Purepecha empire—rivals of the Aztecs in centuries prior to the Spanish conquest of Mexico in 1519.
The site was massive at 13 square km. The traditional surveying method would have taken many years to complete. According to to Fisher the first two seasons they only surveyed about two square kms. With lidar technology they mapped the entire city in just 45 minutes.
A possible Leonardo Da Vinci masterpiece has been discovered behind a 16th Century mural in the Salone dei Cinquecento, which is known as a Renaissance palace. Only made possible from lidar scanning.
Previously undiscovered sites surrounding the Stonehenge area in England have also been found by teams employing cutting edge lidar technology.
The team’s discovered of hundreds of new features that had remained unseen for centuries. The features included more than 15 possible new Neolithic monuments(or little henges), missing stones at Stonehenge itself, and evidence around 60 giant pillars which are believed to have formed a mile-wide super henge close by Durrington Walls.
A big discovery was a hole on the West side of Cursus, which marks the path of the sunrise during solstice if connected by a line to Stonehenge’s heel stone. This find has changed how people see Stonehenge; it is now considered as a monument representing the sun’s movement.
The National Trust in the U.K. recently uncovered 120 new archaeological features while conducting an aerial mapping project on Wallington Estate in Northumberland, England.
The trust utilized a 3D digital map of the landscape to identify both historic woodlands that had been cleared in the mid-1700s, as well as former farming layouts. The oldest prehistoric sites discovered through lidar date back to 2000 B.C.
Lidar has been used to successfully identify ancient earthworks in the northern Everglades of Florida, according to a study published in the United States. After processing, Lidar was used to enhance on the earlier usage of this technology.
Researchers were then able to utilize lower-resolution 2-m data to process the raw data with alternative program tools in order to eliminate some of the vegetation issues that had not been addressed by initially accessible DEMs.
Study of the Hohokam
A study in North America combined lidar data with archaeological data and a GIS platform to examine the hydrology and agricultural techniques of the ancient Hohokam in the American Southwest.
The three-dimensional points produced by lidar made it possible to model the flow of water over the landscape. This demonstrates that prehistoric rock alignments were used to modify both the channel and surface flow of water.
As we can see, lidar technology has been used to uncover many new archaeological sites around the world and speed of the process of surveying tremendously. This technology is helping researchers to better understand our past and learn more about the people who came before us.
We can only imagine what else we will discover with this amazing tool in the future.