The Preservationist's New Superpowers
Technologies such as ground-penetrating radar, thermal imaging, laser mapping, photogrammetry, and geographic information systems are aiding efforts to save historic places
Last fall, 150 years and six months after a 10-inch mortar round arced above Fort Sumter and exploded, launching the Civil War, Peter Aaslestad bobbed in a small boat in Charleston Harbor, aiming his camera lens at one of the fort’s five pockmarked ramparts. Part of a team charged with developing a maintenance plan, he was there to create a baseline set of measurements to help, in his words, “keep the ruin alive.”
Had he been tasked with the challenge of measuring a water-locked pile of bricks earlier in his career, Aaslestad says he would probably have told the National Park Service, which manages the fort, “rent me an apartment in Charleston for the summer, maybe for two summers, and I’ll get started.” Instead, the Staunton, Va.-based architect was on site for just three days. Rather than equipping himself and a small army with measuring tapes and ladders and scuttling crablike on the foundation rubble to beat the flooding tide, he circled the fort in a 17-foot Boston Whaler, snapping photos with a digital camera. Back home, he plugged those photos into a computer program that rectified them to scale, giving them the accuracy of measured drawings. The process, called photogrammetry, has been around as long as modern photography, but digital technology has made photogrammetry lightning fast and put it into the hands of preservationists.
Next, Aaslestad gave his hybrid photo-drawings to project lead Joseph K. Opper-mann, a preservation architect based in Winston-Salem, N.C., who is using them to identify the fort’s building materials and phases. The same images will allow Oppermann to specify a long-term repair and maintenance plan, down to the individual brick. “I have always used photographs, but they weren’t scaled,” Oppermann explains. “Here, you get the definition and detail of a photograph with the scale of measured drawings.”
Although “preservation technology” might conjure images of pencils, sketchbooks, mortar trowels, and putty knives, the same technological revolution that gave us the Internet, brain scans, and smart phones is arming practitioners with new abilities akin to superpowers. With computers and laser scanners, preservationists can quickly and automatically size up a project and manage vast databases of information. They can do complex 3-D simulations to anticipate (and prevent) the ravages of time, including wind, water, and seismic damage. Using thermal imaging, ground-based radar, and sonography, they can peer beneath unbroken ground or see through centuries-old walls to assess conditions hidden from the human eye.
Such cutting-edge technology played a prominent role in one of the most ambitious residential preservation projects in modern times—the five-year restoration of James Madison’s Virginia home, Montpelier, completed in 2008. After buying Montpelier in 1901, the duPont family converted the 22-room neoclassical brick home into a lavish, 55-room mansion. The National Trust for Historic Preservation has managed the house since 1984 and partnered with the Montpelier Foundation in 2000. In 2003, when the Montpelier Foundation undertook the building’s preservation a single question begged an answer: Was there enough material from James Madison’s original house to justify a complete period restoration?
To find out, a team began the meticulous process of peeling away wall sections layer by layer in strategic locations throughout the house. “It was like an archaeological excavation turned up on edge,” recalls the Virginia-based architectural historian Mark Wenger. Aaslestad brought his photogrammetry gear. As each layer came off, he would photograph the wall and rectify the photographs to scale, creating a digital photo map of the above-ground “excavation site.” The architectural sleuths dated the layers, identifying elements such as nail types and saw marks. They took samples from each layer of plaster, logging every detail into a central computer database. For the most important or revealing excavations, they created annotated slideshows that illustrate the discovery work, like peeling away layers of an onion. In the space of a few minutes, viewers can see the work that transpired over days and weeks. The digital technology “helped us make the most of the information we harvested,” says Wenger. “Somebody who was very smart and had a very big hard drive between his ears could possibly do all that, but I couldn’t.”
The search ultimately justified a period restoration, and though a preservationist’s goal is typically to minimize any damage to the historic fabric, in this case the team continued excavating the walls, stripping away everything added after about 1812.
Nondestructive testing was the directive during a 2005–2008 exterior renovation of the Guggenheim Museum in Manhattan. Extensive cracking had appeared in the exterior surface of Frank Lloyd Wright’s spiral concrete masterpiece. But no one knew what lay beneath the cracks. Was the interior concrete structurally sound? Did it contain enough reinforcing steel? Workers could have dismantled parts of the structure or drilled bore holes, but a cardinal rule of the Secretary of the Interior’s Standards for the Treatment of Historic Properties is the “retention of all historic fabric.” Adhering to this mandate, highly trained professionals from GB Geotechnics, an international firm specializing in nondestructive evaluation of buildings, combined the use of impulse radar, metal detection, and acoustic inspection to create an image of what lay inside the concrete. A complete investigation of the building’s exterior walls confirmed they were unusually thin and contained a disproportionate level of steel reinforcement. This information vastly reduced the need for core samples, and targeted what sampling was needed to the areas of most structural interest to the project team.
The Colorado-based Atkinson-Noland & Associates, Inc., a structural engineering firm that also specializes in nondestructive testing, used similar ground-penetrating radar to “see” below the headstones in the historic cemetery at Trinity Church in Manhattan. A centuries-old retaining wall needed to be shored up, but over time, grave markers had been moved. One slip of the shovel blade could damage an ancient grave. By rolling his radar unit over the historic plot, engineer and firm vice president David Woodham located graves and other obstructions. This summer, a preservation contractor will finish the job by safely burying tie-backs to anchor the wall.
“It’s like medical technology,” Woodham says. “A number of tools—ultrasound, MRIs, X-rays—let a doctor know more about what’s going on inside you without having to cut you open. Technology allows us to do this, too.”
Other technology is helping preservationists plan for the future. The Oakland-based nonprofit organization CyArk (“cyber archive”), for example, uses 3-D imaging to document the world’s heritage sites for preservation and education. CyArk is the brainchild of Barbara and Ben Kacyra, who developed the first fully integrated laser 3-D imaging, mapping, modeling, and computer-aided-design (CAD) system, now used by surveyors and engineers around the world. Archaeology buff Ben Kacyra was shocked when the Taliban blew up the 175-foot-tall Buddhas in the Bamiyan Valley of Afghanistan in 2001, and turned his invention into a preservation tool.
In nearly nine years, CyArk has scanned and archived more than 30 sites around the world, including the Presidio of San Francisco, Easter Island, the Mayan temple at Tikal, and Mount Rushmore. If one day Abe Lincoln’s nose falls off the colossal South Dakota sculpture, CyArk’s data cloud could aid in the repair.
Uganda’s Kasubi Tombs illustrate how important this work can be. Originally built in 1884, the compound of wood, wattle-and-daub, and thatch buildings is a UNESCO World Heritage Site and popular tourist attraction for visitors to Uganda’s capital, Kampala. On March 16, 2010, fire destroyed the tombs, which housed the remains of four kings of the Bugandan people, the country’s largest ethnic group.
A year before the devastating fire, Scott Cedarleaf had spent a day at Kasubi surveying the main tomb, courtyard, and gatehouse using a 3-D LiDAR (light detection and ranging) scanner he had checked on his flight from California. He was there on his own dime to scan the tombs and dome-shaped thatch-roofed mausoleums as part of a collaboration between SkyBucket 3D, his commercial imaging and modeling company, and CyArk.
Cedarleaf spent hours at the Bugandan holy site, strategically positioning his scanner and collecting data. LiDAR works similarly to a highway patrolman’s speed gun, measuring the time it takes for a laser beam to boomerang back to the device. Instead of measuring the speed of a vehicle, however, the 3-D scanner measures distance. Using a theodolite, the traditional surveyor’s instrument, a two-person team might gather more than 1 million data points in a day’s work. In the same span of time, Cedarleaf’s advanced LiDAR equipment, which operates automatically and at the speed of light, can capture more than 1 billion data points. In a single day at the tombs, he collected more than 90 million measurements— every nook and cranny—which enabled him to create an eerie, hologram-like digital point cloud of the tombs.
Before archiving Cedarleaf’s data, CyArk converted the information into the kind of sectional CAD drawings and site plans that architects and builders use. Should the government of Uganda and the Bugandan people decide to rebuild, thanks to Cedarleaf and CyArk, they now have a digital map to guide them. “An unforeseen tragedy like this is the whole reason CyArk exists,” Cedarleaf says.
Laser scanning isn’t the only technology initially developed for another field now being used by preservationists. Atkinson- Noland & Associates, the company that rolled radar over the Trinity Church cemetery, was recently hired to work on a late- 19th-century assay office in Wallstreet, Colo., a former mining community west of Boulder. Made of rough-cut local granite with grapevine mortar joints, the building, now a museum, was plagued by a moisture problem. Woodham came up with the idea of using moisture probes, designed to let farmers know when it’s time to irrigate. Last winter, he installed eight Popsicle-stick-sized sensors in different locations in the lower-level walls and in the ground. Wires from the sensors were connected to a computer recording moisture levels at regular intervals. Woodham will then interpret the data to determine the root cause of the problem. If it’s surface runoff, he might recommend an intercepting trench; in the case of rising damp from the water table, ports in the masonry walls would help release the moisture. Twenty years ago, preservationists might have simply repaired the damage. Today, technology allows Woodham’s firm to pinpoint the cause and prevent its recurrence.
A group of preservationists in Tacoma, Wash., is using a different kind of technology to be proactive. When the city’s historic preservation office hired Artifacts Consulting to conduct a survey, members of the firm decided to use Tacoma’s existing geographic information systems (GIS) database to stretch their limited budget. A GIS database is a computerized map that manages layers of information about a place—real estate boundaries, sewage lines, zoning districts, and so on. “We could have done a traditional survey, where somebody goes out, makes notes about the architecture of the buildings, and does some evaluations, and we could probably have included about 100 buildings,” says Artifacts historic preservationist and National Trust Trustee Mary Thompson. “But we decided for planning purposes it would be more useful to have an overview of where the oldest structures are and how they hang together in districts or potential districts.” Instead of surveying 100 buildings in depth, the firm used the GIS database to do a cursory analysis of 45,000, flagging all properties built before 1965. If somebody comes in for a permit or if the city’s going to widen a street, the potentially historic buildings are flagged. And it’s now clear which districts need more intensive historic surveys. Such an overview was nearly impossible in the past, which meant that old structures and even entire neighborhoods could fall through the cracks. With this survey, the opposite is true: The city can anticipate when districts will be considered historic.
“In terms of historic preservation planning, we’ve always been at the mercy of how many surveys were done in the past,” Thompson says. “A traditional historic preservation survey is a mere snapshot in time. We’re trying to project into the future.”
Like a lot of new gadgetry, preservation technology can be costly. Architect Peter Aaslestad who surveyed Fort Sumter has invested tens of thousands of dollars in camera gear, computers, and photogrammetry software. Structural engineer Woodham’s ground-penetrating radar cost his firm $25,000. A 3-D laser scanning system like the one Cedarleaf used in Uganda can cost well over $100,000. But these tools can pay for themselves by increasing efficiency (smaller crews, less time on the clock) and removing some of the speculation inherent to working on structures with designers and builders who are long dead.
“If you look at traditional budgets from 15 years ago, when we didn’t have any of this technology, we would throw in a 25 to 30 percent contingency fee for unknown risks,” says Philadelphia-based George Skarmaes, a preservation architect who has led teams responsible for the restoration of the Virginia State Capitol and President Lincoln’s Cottage. That’s an extra $2.5 million to $3 million on a $10 million project. For a fraction of that extra cost, a GCS project team could consider a nondestructive examination program and better manage risk. “If the contingency goes from 30 percent to 5 percent, the financial realities of a project can change dramatically.”
Skarmaes is quick to point out that high-tech preservation tools have their limitations. They’re useful only during certain stages of the process, typically the crucial planning stages. “You need to have the right craftsmen work on a project. That will never change,” he says. But technology can aid the craftsperson as well, whether he or she uses a laser cutter in place of a handsaw or CAD software rather than a drafting table.
Back when Skarmaes worked for the architecture firm Vitetta, one of his colleagues, Joseph Sorrentino, was a brilliant holdout, still drawing by hand and creating “absolute works of art.” One day, Sorrentino taught himself to use a CAD program. “Here was one of the greatest sets of hands I’d ever seen in my life, and all of a sudden he’s doing CAD drawings,” remembers Skarmaes. His first thought was, “What a sad and dark day.” But the man’s gifts transcended the technological shift. “If you look at his CAD drawings today, they’re out of this world. Is there a danger to relying on technology? Yes. But if you use your brain and use the technology correctly, then the end result can be terrific.”