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Backstage Pass to North Dakota History

This blog takes you behind the scenes of the State Historical Society of North Dakota. Get a glimpse at a day-in-the-life of the staff, volunteers, and partners who make it all possible. Discover what it takes to preserve North Dakota's natural and cultural history. We encourage dialogue, questions, and comments!

Timothy Reed's blog

Drone Mapping an Archaeological Site

Archaeologists have been seeking higher vantage points to photograph and map archaeological sites for decades. Cameras mounted under balloons or kites, cameras in aircraft or powered parachutes, or photos taken from ladders, mechanical lifts, or even a slight hill — archaeologists have used them all at one time or another to gain an aerial perspective and document site excavations.

black white image of farmers in field

Some early methods of photography used by archaeologists were not for the faint of heart. A fully extended ladder stabilized by wires was used to photograph excavations at the Oldham site located in Charles Mix County, South Dakota. (River Basin Survey photograph 39CH7-405).

two men working in a crane bucket

Stanley Ahler of the PaleoCultural Research Group and Lloyd Jensen of the State Historical Society of North Dakota use an articulating boom lift to photograph excavations at Menoken Indian Village State Historic Site in August 2005. (Note: Both men were wearing a protective safety harness.)

A relatively new method of mapping features at archaeological sites is drone mapping. Since 2017, I’ve written about flying the State Historical Society’s quadcopter (or “drone”) to photograph state historic sites multiple times. Most recently, I’ve written about using our drone to photograph Cannonball Stage Stop and Fort Mandan Overlook State Historic Sites.

Fort Mandan Overlook offers a great example of using a drone to generate a highly detailed surface map of features (such as house depressions, fortifications ditches, or topography) present on an archaeological site. The aerial images are processed using specialized software. State Historical Society archaeologists drone mapped the Fort Mandan Overlook site on July 25, 2019.

Fort Mandan field overlooking forest

Aerial image of Fort Mandan Overlook State Historic Site in McLean County, North Dakota, taken by quadcopter on July 25, 2019. The fortification ditch visible in this image was a defensive structure constructed sometime in the late-18th to mid-19th century. The site was initially occupied as early as the 1300s. The site overlooks the former location of Lewis and Clark’s Fort Mandan, which was washed away by the Missouri River soon after the expedition passed through the area.

Drone map with 5 red GPS points

To prepare for a drone mapping mission, State Historical Society archaeologists established a series of “ground control points” at the site using a centimeter-level accuracy Global Positioning System (GPS) unit and ground targets. The targets help to accurately align the images captured by the drone and supplement the GPS coordinates tagged to each of the images.

white and black square checkered flag

Six of these targets were placed on the ground surface at the site, and centimeter-precise GPS coordinates were collected prior to mapping.

Prior to flying the drone at the site, a detailed “mission plan” was created using Pix4D capture, a software specifically designed for drone mapping. The mission plan directed the drone to fly in a grid pattern over the site area at a specific altitude and collect images of the ground surface that would be mosaicked or “stitched” together later. The resulting 356 images are at a very high resolution, and each image has extremely detailed locational information associated with it.

mapping software on tablet screen

An image of the Pix4D Capture software during our “mission” at Fort Mandan Overlook. An aerial image of the area serves as a basemap. The mission grid is visible, and the green dots indicate the position of collected images.

aerial view of a field with trees bordering it with 1 red GPS point

One of the 356 images collected by the drone at Fort Mandan Overlook. This image is in the southeast corner of the site. The original image was also tagged with GPS coordinates.

After the grid mission was flown, the images collected were processed using photogrammetry software called Agisoft Metashape. Photogrammetry is the process of obtaining information about objects or the environment by analyzing and interpreting photographic images. The software corrects the inherent distortion introduced when we photograph three-dimensional objects (like artifacts or the ground surface), and then displays the images on a flat surface (like a computer monitor or a printed page).

In this case, the images used in an analysis of the surface of the Fort Mandan Overlook site were those collected by our drone. Photogrammetric image analysis is an area of research the State Historical Society’s Chief Archaeologist Andy Clark is quite familiar with, and he processed the 356 overlapping images collected using this specialized software to produce measurably accurate three-dimensional models and photographs. I’ve included a couple brief descriptions below.

photogrammetric software screencap

An image from the photogrammetric software used to process images collected at Fort Mandan Overlook. The blue rectangles at top indicate the relative positions of the images collected by the drone. The three-dimensional image below is the result of “stitching” the images into a mosaic using a pixel-matching algorithm. The individual images collected by the drone are seen at the bottom of this screenshot.

digital surface model of Fort Mandan Overlook

A digital surface model (DSM) of Fort Mandan Overlook. DSMs contain elevation data of the terrain and other features present on the surface (like trees and structures). In this image, the red, orange, and yellow colors represent lower elevations at the site, so the bluff edge at the site can clearly be identified.

relief map of Fort Mandan Overlook

Image showing a relief map of Fort Mandan Overlook. A relief map is a 3-D representation of a surface, with the Sun’s position indicated. Relief maps tend to look realistic and can be useful in interpreting a three-dimensional surface. The fortification ditch and drainages present at the site are clearly visible in this image.

orthophotograph showing Fort Mandan Overlook

An orthophotograph showing Fort Mandan Overlook. Orthophotographs are aerial images that have been geometrically corrected to minimize distortion so that scale is uniform and features are measurable. Distances and area can be accurately measured using orthophotographs.

State Historical Society archaeologists have “drone mapped” five archaeological sites in this manner so far. While my focus has been primarily on using the drone to document and map archaeological sites, some of my coworkers have begun using similar techniques to model artifacts like stone tools, pottery, and even historic clothing. Keep an eye out for new 3-D projects described in future blog entries!

Flying High: New UAV Flights at North Dakota State Historic Sites

Among the many things about my job I truly enjoy are the opportunities that arise, for one reason or another, to get out of the office on a beautiful, sunny day! Being able to visit one of the state historic sites that I’ve never been to is an added bonus. Even better if I get to visit TWO sites. And if I also have the opportunity to fly our quadcopter at those sites . . . well then, you’ve just about described a perfect work day for me!

I’ve blogged about flying the Society’s quadcopter (also known as a “drone,” “unmanned aerial vehicle,” or “UAV”) several times before [check out some of my earlier entries about flying a drone at North Dakota’s state historic sites, including Double Ditch Indian Village, Menoken Indian Village, Fort Clark, and Fort Rice, among others.]

To date, I’ve piloted a UAV at 13 prehistoric or historic archaeological sites in North Dakota, including 9 state historic sites managed by the State Historical Society. I hope to fly a great deal more in 2019 and beyond. The technology, opportunities for application, and regulatory environment have all evolved since our earliest flights in 2014. But the reasons for these flights all share the same basic purpose: to document preservation concerns about cultural resources, and to enable interpretation and management of North Dakota’s state historic sites.

Aerial view of Cannonball Stage Stateion State Historic Site

Aerial image of Cannonball Stage Station State Historic Site, Grant County, North Dakota, taken by State Historical Society quadcopter on October 17, 2018. View is to the east. The altitude of the quadcopter was 400 feet and wind speed was 5-7 miles per hour when this image was taken. Surface depressions marking the location of two dugout structures and a barn are visible near the fenced area.

I was fortunate to fly the quadcopter at two sites on a beautiful fall day in October 2018. I’d like to share some images and video from these recent flights over the Cannonball Stage Station and Fort Mandan Overlook State Historic Sites. Cannonball Stage Station and Fort Mandan Overlook are among the lesser visited of the 57 historic sites in our state. Both are in beautiful, remote locations and definitely off the beaten path.

Located near Raleigh, in Grant County, North Dakota, the Cannonball Stage Station was the fifth stop after Bismarck on the Bismarck to Deadwood Stage Trail. For a brief period from 1877 to 1880, a booming stagecoach line linked the westernmost stop of the Northern Pacific Railroad in Bismarck to the gold fields of the Black Hills. Travelers would have the opportunity to have a short rest and a quick meal here while horses were swapped, and the stage was quickly back on its way. This unique period in North Dakota is well- interpreted at the site, picnic facilities are available, and it’s a peaceful spot. Earthen dugouts clearly visible at the site represent the locations of the stage office, another building, and a barn. Check out a video from a recent UAV flight at Cannonball Stage Station State Historic Site.

Aerial view of Fort Mandan Overlook State Historic Site

Aerial image of Fort Mandan Overlook State Historic Site, McLean County, North Dakota, taken by State Historical Society quadcopter on October 16, 2018. View is to the northwest. The altitude of the quadcopter was approximately 100 feet above ground surface, with winds gusting to 30 miles per hour when this image was taken. Two historical markers present at the site are visible in this image, as well as the dramatic bluff edge.

Fort Mandan Overlook State Historic Site is located near Washburn, North Dakota, in McLean County. This site overlooks the former location of Fort Mandan, constructed and occupied during the fall and winter of 1804–1805 by the Lewis and Clark Expedition. The fort location has long since been eroded away by the nearby Missouri River, but there are other stories here as well. During archaeological investigations conducted at the site by the State Historical Society in 1991–1992, a fortification ditch dating to the late 1700s–early 1800s and a Plains Village campsite dating to the 14th century were documented. Interpretive signs are present, and the viewshed from this location is stunning. Watch your step, though—the bluff edge is steep. Check out the video from a recent UAV flight at Fort Mandan Overlook State Historic Site.

I was happy to add Cannonball Stage Station and the Fort Mandan Overlook to the list of state historic sites I’ve visited and documented from the air. Someday, I’m going to get to every one of them. In the meantime, I hope you’ll consider a trip sometime soon to these or one of the many other state historic sites in North Dakota. I hope the video links in this blog help to give you just a hint of the historical significance and natural beauty of these locations. The videos were a lot of fun to shoot! Many thanks to the video editor who helped me out on short notice, and to the Bismarck/Mandan local musicians that provided the accompanying music. Enjoy!