Western Heritage Services Inc. reveals buried historic fort through ‘incredible’ image resolution from an Aeryon Scout sUAS.
Western Heritage Services Inc. was founded in 1990 to serve the growing need for specialized heritage services. Today, Western Heritage is a premier provider of heritage services in Canada and around the world.
INDUSTRY: Archaeology Services | REGION: Canada
The image of archaeology that persists in the public mind is of students and professors on their hands and knees painstakingly brushing dirt from buried artifacts. But while such manual activities remain essential, archaeology has been revolutionized by technology. Today, a single scientist using ground-penetrating radar, magnetometry, or soil analysis can generate vast quantities of data about what lies beneath the surface.
Getting a clear picture of the surface itself, however, remains a challenge. For many years, the only way to obtain a detailed map of the surface in a timely manner has been to hire a qualified pilot to fly over the site and take photographs. This method for collecting images tends to be expensive and yields resolutions of only about 4 in. (10 cm), which typically isn’t detailed enough for smaller, more recent sites, where archaeologists are faced with much subtler variations in surface features and elevations.
To obtain an aerial map of the relatively remote Original Humboldt site (a strategic outpost of the Canadian military during the Northwest Rebellion of 1885, shown in Figure 1), Western Heritage faced the prospect of hiring a pilot to fly an airplane from Alberta into Saskatchewan and take photographs of an area much larger than the site itself. With funding available for only one week of work on the site each year, Western Heritage had to forego aerial mapping and rely on existing, much less detailed ground-based surveys to try and identify where excavations could yield the best results.
Then, at an archaeology conference in 2011, Carmen Finnigan, Western Heritage’s remote sensing scientist, listened with increasing excitement to a presentation about the recent breakthroughs in surface mapping provided by small unmanned aerial systems (sUAS). She learned that UAS can provide aerial photographs and a digital terrain map in as little as a few hours, and at a lower operational cost than traditional methods.
In 2013, Western Heritage approached Les Klein, President of Civil Works Consulting Inc., with its requirements. Civil Works Consulting Inc. provides aerial imagery (using the Aeryon Scout) and construction services for its clients, so Klein had the knowledge and expertise to capture the required images and data.
Western Heritage needed a UAS that could:
- Be transported easily and inexpensively to a remote site.
- Be safely and efficiently operated without requiring the experience and training of a commercial pilot.
- Provide a stable platform for an aerial camera in the high winds of the Saskatchewan prairie.
- Accurately, repeatedly, and autonomously follow a survey grid.
- Operate at an altitude of 164 ft. (50 m).
- Capture thousands of images in a few hours.
- Take photographs with a ground resolution of at least 4 in. (10 cm) and an overlap of 60 percent to ensure the accuracy of the 2D and 3D outputs.
- Provide the data required to create a digital terrain map with sub-meter vertical elevation accuracy and sub-meter horizontal posting (the distance between each elevation measurement).
In August 2013, Klein drove to Humboldt, Saskatchewan, the city closest to the Original Humboldt site, with the Aeryon Scout sUAS and all of its components packed in its case in his truck. Upon arrival at the site, he needed only a few minutes to set up the Scout sUAS and its base station, and create the flight plan. After two hours of data capture, the wind exceeded 25 mph (40 kph) and the gusts became too strong to operate safely.
During the five hour flight on the second day (wind speeds were approximately 15 mph (24 kph), the Scout followed a tight grid pattern across the site, taking photographs with the Aeryon Photo3S™ camera payload. The Scout automatically returned to base for fresh batteries every 20 minutes, each time resuming its flight plan exactly where it left off. Using portable generator, Klein was able to recharge the batteries even though the site was in such a remote location.
Ms. Finnigan was surprised by how small and quiet the Scout was when she saw it in operation, “Les told me he had seen birds fly right up to it in the sky.”
With the photomapping complete, Klein detached the Photo3S payload, snapped on a GoPro HD HERO3 payload, and re-launched the Scout (Figure 2). With the live feed from the GoPro camera displayed on the Scout’s control tablet, the archaeologists were able to see the aerial view (Figure 3) of the site in real time, and could advise Klein where to position the Scout to capture the best images.
After downloading nearly 1230 images from the Photo3S payload, Chun Chen, Western Heritage’s geomatics manager, used Pix4Dmapper software to stitch together the overlapping images into a single, geo-referenced orthomosaic (Figure 4), and then generated a digital terrain model.
By combining the aerial photographs and the digital terrain map (Figure 5), Western Heritage has been able to produce a highly accurate base map that it can use to tie in all of the current work on the site and help confirm their hypothesis that the low sandy hill was the location of Original Humboldt. Understanding the shape of the hill helped determine how the hill was formed, how the site was used and fortified. This information will also help the Western Heritage team plan their work on the site each year going forward.
In addition, the high level of detail in the images has enabled Western Heritage to identify all of the grid stakes and excavation units at the site. This will assist in correlating all of the previous work done on the site.
“The image resolution we achieved using the Scout was incredible,” says Ms. Finnigan, “5 cm, much better than the 10 cm we can get from an airplane.” The orthomosaic image produced with Pix4D was 1.5cm/pixel resolution.
As seen in Figure 3, the aerial photographs also revealed an intriguing feature that could not be detected from the ground: discolouration of the soil at the fort. The origin of this discolouration is not known at the current time but may represent a new area for exploration.
For Ms. Finnigan and Ms. Chen, using the Scout to obtain aerial images has literally added a new dimension to archaeological science. They look forward to obtaining aerial thermal images using the near infrared spectrum sensors of the Scout’s Thermal FLIR camera option.
For Jennifer Hoesgen, director/curator of the Humboldt District Museum and Gallery, the aerial images will help the public understand the layout and features of Original Humboldt, and to make the site more accessible. “Visuals give museum visitors something to get excited about and that translates into more public support for learning about the history of Saskatchewan and western Canada”, she says.
|Figure 1. Original Humboldt, Saskatchewan, 1885||Figure 2. Aeryon Scout at Original Humboldt|
|Figure 3. High resolution images reveal details about Original Humboldt not possible with other methods of data capture.|
|Figure 4. Stitched images are used to create this orthomosaic output.|
|Figure 5. Digital terrain map. The contour lines are 8 in. (20 cm).|