A group of 10 University of Wisconsin-Madison civil and environmental engineering graduate students is monitoring the structural health of a 150-year-old Superior lighthouse.
With Jesse Hampton, an assistant professor of civil and environmental engineering at UW-Madison, the students are studying the Au Sable Lighthouse located in the Pictured Rocks National Lakeshore on Lake Superior in Michigan’s Upper Peninsula. The lighthouse, first constructed in 1874 at Au Sable Point, is part of a complex of structures comprising the Au Sable Light Station, which was built by the U.S. Lighthouse Service and later consolidated under the U.S. Coast Guard.
Using fiber-optic cables wound helically around the lighthouse’s central stairway, Hampton’s students instrumented the lighthouse in coordination with the U.S. Army Engineer Research and Development Center’s Construction Engineering Research Laboratory and the National Park Service.
“With fiber-optic sensing, we can monitor high-frequency and low-frequency deformations,” Hampton says. “Low frequency could be, for example, if there’s any cantilever beam action from the wind or a big storm pushing against the structure. High frequency could be any sort of vibration from the ground or people moving through the building.”
Nathan Opperman and Gowshikan Arulananthan are two geological engineering PhD students in Hampton’s research group. Opperman says the monitoring system yielded gigabytes’ worth of data in the weeks since the researchers installed the fiber optic cables.
The data shows a cyclical pattern that coincides with the daily rise and fall in temperature, (a type of low-frequency change as the structure expands and contracts). By looking at high-frequency acoustic data, the team can measure foot traffic through the site.
A three-dimensional image created from LIDAR point scans. Hampton’s students took incredibly detailed scans of the Au Sable Light Station, which they will use to supplement their monitoring efforts, and to create augmented and virtual reality tools to view the structure. Submitted photo.
“We can see movement reflected in our data,” Arulananthan says. “You can see people touring the facility and climbing the stairs all the way up to the top. We were curious to see if we could look at the data to find out how many events like that occurred in a given day, and we definitely can.”
The National Park Service preserves and maintains historically significant structures and cultural landscapes such as the Au Sable Light Station. There’s a chance the UW-Madison monitoring equipment may remain in place for up to 15 years, which would yield an unprecedented period of data collection.
“That would be one of the only data sets in existence that really monitors climate impacts on a historic structure over a long period, especially with distributed fiber optic sensing,” says Hampton.
While on-site, the researchers used LIDAR to take 3D scans of the lighthouse, then used those scans to create extremely detailed—using tens of millions of data points—point cloud images of the structure. These images are being used to develop augmented and virtual reality site visits and inspections, allowing anyone to access scanned structures regardless of location.
Those scans also have value for monitoring the historic structure’s health. “Let’s say, for example, there’s a crack where the staircase connects to the wall. We’d be able to tell over time that’s an area that needs some attention,” Opperman says. “LIDAR is essential for us to locate where strains are happening because it’s so sensitive. It’s able to pick up things in the sub-millimeter range.”
National Park Service Historical Architect John Rosemurgy says the data collected at the 87-foot-tall brick masonry lighthouse tower will provide insight that has, so far, not been available. “We know that the structure has been resilient over the past 150 years but don’t know to what extent it undergoes movement and correction from environmental forces such as storm events or even seismic activity,” he says. “The collected data that Jesse and his team are analyzing will help us better tailor future preservation efforts.”
Though the work is part of an ongoing research project with the Department of Defense, Hampton also saw an opportunity to add a new dimension to his class, CEE/GLE 534: Nondestructive Evaluation. Typically, the class covers techniques like X-ray, ultrasound, acoustic emission and more. For the fall 2024 semester, Hampton took the class on a three-day field trip to set up nondestructive equipment at the site and later in the semester, ask the students to analyze the data they collected.
“One of the things that’s exciting about a class like this is they actually have exposure to real data that they collected,” Hampton says. “They understand how it was collected. They can use that experience and develop different analytical tools that they’ll use for a long time, even after they graduate.”
Opperman and Arulananthan both took Hampton’s nondestructive evaluation course. The in-the-field experience was new for Arulananthan, who says he enjoyed it and the collaboration taking place among UW-Madison and its partners. Opperman, who did more field work earlier in his education, says Hampton’s class was a unique experience.
“Jesse’s taking a really bold approach, and a very admirable one, of having the class built into the structure of the research project itself,” Opperman says. “It’s a lot of the class’ first exposure to the type of data we’re using, so kind of like throwing people into the deep end and expecting them to flourish in that. And I think that’s a good way to teach, and leads to a lot of growth and development of people’s research ability, project management and communication skills, because we’re working in groups.”
In the past, Hampton has taught the course every other fall, but with the new design incorporating field trips and data collection efforts, he is transitioning it to being offered every fall (open for fall 2025). The class will incorporate similar projects, using bridges or other structures students can use for real-world experience.
The Au Sable Lighthouse instrumentation is part of a larger project with colleague Hannah Blum, an associate professor of civil and environmental engineering. They’re monitoring historic structures with support from the U.S. Army Engineer Research and Development Center’s Construction Engineering Research Laboratory (ERDC-CERL).
“It is truly exciting to see research that UW-Madison and ERDC-CERL have been working on for several years culminate in this first field experiment to innovate how the government monitors and manages its historic structures,” says Dawn Morrison, ERDC-CERL team lead for the assessing and monitoring historic structures initiative, in a news story about the collaboration. “We are really grateful to the National Park Service for supporting this project and making the Au Sable Lighthouse available.”
Featured image caption: Civil and Environmental Engineering Assistant Professor Jesse Hampton’s students pose at the top of the Au Sable Lighthouse, which overlooks the Lake Superior shoreline from Michigan’s Upper Peninsula. Hampton’s group instrumented the lighthouse with fiber optic equipment to monitor it long-term. Submitted photo.