Study recommends use of non-intrusive tool to scan Guam's prehistoric sites
By Mar-Vic Cagurangan
Military construction and commercial development on Guam often lead to the discovery of buried archeological resources, but the fieldwork preceding these projects can cause disturbance to the island’s ancient cultural landscape.
Thanks to groundbreaking non-intrusive technology called "light detection and ranging," simply known as “lidar,” now it is possible to measure and map prehistoric structures prior to excavations and the commencement of any project.
Griffith University’s Center for Social and Cultural Research piloted lidar on Guam, where archeologists and mapping specialists identified ancient sites from the Latte, Spanish and Modern periods using the technology.
Victor Hara Torres, a local archeologist and mapping specialist, said the lidar experiment was conducted in the central and western parts of the island.
“Some of the sites we have identified have been discovered before, but using the lidar, they became more noticeable,” said Torres, one of the authors of a research paper titled “Effectiveness of Airborne Lidar for Identifying Archaeological Sites and Features on Guåhan."
The paper explores the remote sensing technic to help better facilitate archeological research and historic preservation on Guam.
Torres said the study offered an interesting look at how modern technology can contribute to the discovery and understanding of the past.
"The benefits of using this technology are great for the community of Guåhan as it offers a non-invasive way to investigate sites and assist with their cultural heritage management,” states the paper published in the Journal of Computer Application in Archaeology.
Lidar is a remote sensing technique that involves sending out laser pulses and calculating the return time from surface reflections.
Andrea Jalandoni, the paper's lead author, described lidar as “a very effective way to see and map the sites that are obscured and may not be visible due to vegetation.”
The research team initially scanned the target sites for latte structures, but later expanded the survey to include agricultural terraces, gigao (fish weirs), water wells, Spanish Period roads, bridges, structures, and forts; and Modern Period examples of WWII gun positions, bomb craters, developments, and fuel tank berms.
“This pilot study using lidar has opened my eyes to new sites and historic landscapes I worked in, but never envisioned had such unrealized potential,” said Boyd Dixon, a co-author of the paper.
The research team, however, identified the vegetation on Guam as a general challenge to using lidar for detecting archaeological sites.
"Archeological features are often intermingled with vegetation, especially in dense tropical forests or savanna grass areas, making it difficult to use height above ground as a filtering technique," the authors said.
This necessitated the need to use airborne lidar. The study found that the laser can penetrate a tree canopy the same way sunlight does, capturing objects on the ground below.
The study found that lidar was less effective in discerning small-scale latte habitations and pre-WWII water cisterns in disturbed and vegetated contexts but has had some utility in identifying larger concentrations of concrete features and bomb craters in a post-WWII Seabee encampment.
The paper's authors suggested that the use of lidar could minimize the potential destruction of Guam’s prehistoric cultural resources as the island seeks to further expand tourism and the Navy builds more military facilities in preparation for the relocation of 5,000 Marines from Okinawa.
Its potential use in locating latte stones, a significant symbol and treasured birthright to contemporary CHamoru, is especially appreciated when perceived as under threat by military construction and commercial development today," the author said.
In recent years, ancient burial sites and other artifacts were discovered at military project sites in Ritidian and Marine Corps Base Camp Blaz in Dededo. The disturbance of these archeological resources has triggered a conflict between the military and the CHamoru community.
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“As more archaeologists and the community, both CHamoru and Guamanian, become familiar with lidar and what it can offer, this study encourages further exploration to potentially identify additional historic and prehistoric sites,” the authors said.
“The results can lead to better-informed field surveys both in planning stages by targeting potential resources and upon discovery by enhancing documentation of previously unrecognized sites or poorly documented prehistoric habitation and land use sites such as those found in the southern Guåhan uplands,” the authors said.
Maria Kottermair, a mapping specialist, said the pilot project only showed one application of lidar data for Guam, but the technology may also be used for other purposes such as sea-level rise modeling or construction monitoring.
“We have only scratched the surface and there is a lot more that can be done with this technology,” she said.
Despite the challenges and limitations posed by various factors, the authors said the study offered a foundation for “an integrated multi-scale interpretation of archeological features in the prehistoric and historic landscape."
Archeological examinations, the authors said, will succeed "by combining environmental factors, structured expert knowledge, and the automation of archaeological feature detection and extraction that can lead to more archeological sites being discovered.”