A 1.942Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE
The use of LiDAR to support archaeology has been well known within the geospatial community for some time now. Interestingly enough, several individuals outside the geospatial community are just now realizing the potential of LIDAR technologies across all aspects of archaeology. This is not to say that a small group of innovators within this community didn’t pioneer the use of LiDAR. In the late 90’s, several ruins in South America were collected using LiDAR and these ruins continue to be flown with LiDAR today.
All sorts of laser instruments are being used to document ancient locations and artifacts. These instruments range from small desk platform lasers used to scan pottery; tripod laser scanners used to document inscriptions on walls and catalog buildings; mobile systems to record elevation information for large religious sites; and helicopter/fixed wing LiDAR-mounted sensors to search for entire communities and provide important information about known sites.
In 2012, Quantum Spatial (QSI), formally AeroMetric was approached by Committee Films, a production company for the History Channel to survey and process airborne LIDAR data for the Track Rock Site in Chattahoochee National Forest in Northern Georgia for the premier episode for a show called "America Unearthed" because the park would not give access to the production company. Committee Films wanted to capture the entire experience on film for the episode in the middle of July with full canopy.
In short, the premise of the show was trying to link the track Rock ruin site with the Mayans in South America. QSI was just trying to collect useable detailed data. The Optech Onion C300 was used for the collection and the result was excellent. The site was captured during full leaf on using a planned collection of 40 50 ppm at 2300 feet AGL. The premier episode of "America Unearthed" aired on December 21, 2012. This date had been billed as the "end of the world on the Mayan Calendar. As a result of the success of this episode QSI was asked to come back for season two so we could be filmed collecting The Cahokia Mounds in Illinois, just east of St. Louis, MO.
The Cahokia Mounds are believed to be the largest ancient Native American city of the time with about 10,000 Native American people within the immediate city and up to 35,000 Native American people in the region between the years of 600 to 1400. The historic park covers about 3.5 sq miles and contains 80 mounds, but the ancient city was actually much larger. At its largest Cahokia covered about 6 sq. miles and included about 120 human made earthen mounds ranging in size, shape and functions.
According to the locals, the actual historical park is actually relatively unspectacular compared to the rest of the mounds located outside the park. After flying the site and analyzing the data, before reviewing with the show’s host Scott Wolter and Dr. Peter Peregrine Professor of Anthropology at Lawrence University and a Cahokia expert, we noticed a very distinct pattern in an area just northwest of and close to the visitor’s center, and just south of the largest mound as represented in the LiDAR surface model. This turned out to be a trailer park that had been established on the site before it became a national park. The trailer park was not visible on any of the on-line imagery services such as Bing and Google, or in any imagery we had access too. Additionally, QSI had flown the region in 2009 with LiDAR and the trailer park was not visible in that data. It should be noted that the LiDAR surface model was sampled down by 10x as depicted and you can very clearly see the trailer park as indicated above.
In the late spring of 2013, QSI, with the help of Optech, collected data using different types of scanning sensors including terrestrial, mobile and airborne LIDAR scanners for this episode of "America Unearthed" The . Leica ALS-70 was used to collect the LIDAR over the Cahokia Mounds Site. The Optech Lynx Mobile Mapping System was used to scan the production site at the airport and the large mound at the Cahokia site. Additionally, Committee Films wanted to know if we could scan the host of the show and the airplane during the shoot. Optech used an ILIRIS tripod mounded scanner to scan the host and set during the first part of the days filming.
The collection of the actual Cahokia Mounds site was the focus of the production. The host Scott Wolter was trying to link the site with other mound sites in North America as well as Europe. The intent of the LIDAR collection was to collect high resolution LiDAR over the site and look to see if there was any evidence of effigy mounds at the site and see if these mounds have similarities to mounds in Iowa, Ohio and Europe.
The Leica ALS-70 was flown at 1500 meters AGL. The project was planned to fly a set of 11 lines in the North South direction at a 20 degree FOV, 66.3 hertz scan rate, 380.8 KHz repetition rate and 55% overlap, with an airspeed of 160 knots to yield a point density on this set of passes of 18 ppm. Additionally, eleven lines were planned in East- West direction at a 15 degree FOV, 69.5 Hertz scan rate, 383.6 KHz rep rate and 55 % overlap, with an airspeed of 160 knots to yield a point density on this set of passes of 24 ppm. The total point per meter was 42 over the entire project site.
The extensive detail provided by the LiDAR collection provided extreme detail of the site and structures within the site. The close up image of the largest mound shows the detailed capture from the LiDAR sensor. You can see all the detail of the walk way up the south side of the mound as well as the erosion on the west side of the mound from extreme precipitation. This type of detail should be enough to see any type of evidence of effigy mounds.
Similar to the first production in Georgia the Committee Films director wanted to make the filming of the Cahokia Project as real as possible. They filmed in the aircraft while we collected the data over the site from 10:30am to 12:30, which included 40 minutes transit to and from the project location. We were able to process the data while the production company was filming other segments of the episode on site.
The total production for the LiDAR segment of the show lasted from 7:30 am in the morning until 8:00pm in the evening. This resulted in about a total of maybe 10 minutes on the aired episode. It was interesting to see the similarities between LIDAR field crews and film production field crews. The film crews have a lot more pelican cases to drag around than LIDAR crews, but very similar to LiDAR field crews in the mid to late 1990’s.
Once the data had been processed and reviewed Scott and Dr. Peregrine sat down with the author to review the data. They discussed the similarity of the site as it related to other ancient sites and to archaeoastronomy. Archaeoastronomy is the study of how cultures in the past understood the phenomena in the sky and related it back to structures they constructed on the ground.
For example aligning structures as they related to the occurrence of annual solar alignment on a given date like spring equinox or something similar. Scott and Dr. Peregrine did provide several examples based on the LIDAR data that showed similar archaeoastronomy characteristics existed at all the sites being studied for this episode.
Although, there was very strong ties to the archaeoastronomy characteristics it did not appear obvious upon first review that there was a strong tie to effigy mounds at the Cahokia Mounds with the other sites in Ohio, Iowa and Europe. Dr. Peregrine did indicate he felt that here was enough evidence to conclude that effigy mounds existed in all locations to tie them together.
The QSI and Optech LiDAR team conducting this project took extensive steps to remain neutral on how the data should be interpreted or our thoughts as it related to the conclusions drawn in the show. We are not the experts in archaeology, archaeoastronomy and any other profession as it relates to interpreting ancient culture or societies. We just wanted to provide the necessary tools for intelligent information to be provided to the individuals doing the work. It is our job to make sure our data is as thorough, accurate, precise and correct so that the specialists in all fields can use the data to help better understand our world.
James Wilder Young is Vice President of Technology for Quantum Spatial. He has been working in all phases of LiDAR including sensor development, data acquisition, data processing and applications development since 1996.
A 1.942Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE