Tag: Ground-Penetrating Radar

Agency of the Subsurface

[Image: The Heathen Gate at Carnuntum, outside Vienna; photo by Geoff Manaugh.]

Last summer, a geophysicist at the University of Vienna named Immo Trinks proposed the creation of an EU-funded “International Subsurface Exploration Agency.” Modeled after NASA or the ESA, this new institute would spend its time, in his words, “looking downward instead of up.”

The group’s main goal would be archaeological: to map, and thus help preserve, sites of human settlement before they are lost to development, natural decay, climate change, and war.

Archaeologist Stefano Campana, at the University of Siena, has launched a comparable project called Sotto Siena, or “Under Siena”—abbreviated as SOS—intended to survey all accessible land in the city of Siena.

[Image: A few of Siena’s innumerable arches; photo by Geoff Manaugh.]

That project’s goal is primarily to catalog the region’s millennia of human habitation and cultural artifacts, but, like Immo Trinks and his proposed ISEA, is also serving to document modern-day infrastructure, such as pipes, utilities, sewers, and more. (When I met Campana in Siena last year, I was interested to learn that a man who had walked over to say hello, who was introduced to me as an enthusiastic supporter of Campana’s work, was actually Siena’s chief of police—it’s not just archaeologists who want to know what’s going on beneath the streets.)

I had the pleasure of tagging along with both Trinks and Campana last year as part of my Graham Foundation grant, “Invisible Cities,” and a brief write-up of that experience is now online over at WIRED.

The article begins in Siena, where I joined Campana and two technicians from the Livorno-based firm GeoStudi Astier for a multi-hour scan of parks, piazzas, and streets, using a ground-penetrating radar rig attached to a 4WD utility vehicle.

[Images: The GPR rig we rode in that day, owned and operated by GeoStudi Astier; photos by Geoff Manaugh.]

We stayed out well past midnight, at one point scanning a piazza in front of the world’s oldest bank, an experience that brought back positive memories from my days reporting A Burglar’s Guide to the City (alas, we didn’t discover a secret route into or out of the vault, but just some fountain drains).

In Vienna, meanwhile, Trinks drove me out to see an abandoned Roman frontier-city and military base called Carnuntum, near the banks of the Danube, where he walked me through apparently empty fields and meadows while narrating all the buildings and streets we were allegedly passing through—an invisible architecture mapped to extraordinary detail by a combination of ground-penetrating radar and magnetometry.

“We want to map it all—that’s the message,” Trinks explained to me. “You’re not just mapping a Roman villa. You’re not mapping an individual building. You are mapping an entire city. You are mapping an entire landscape—and beyond.”

An estimated 99% of Carnuntum remains unexcavated, which means that our knowledge of its urban layout is almost entirely mediated by electromagnetic technology. This, of course, presents all sorts of questions—about data, machine error, interpretation, and more—that were explained to me on a third leg of that trip, when I traveled to Croatia to meet Lawrence B. Conyers.

[Image: A gorge leading away behind the archaeological site I visited on the island of Brač, Croatia; photo by Geoff Manaugh.]

Conyers is an American ground-penetrating radar expert who, when we met, was spending a couple of weeks out on the island of Brač, near the city of Split. He had traveled there to scan a hilltop site, looking for the radar signatures of architectural remains, in support of a project sponsored by the University of Colorado at Boulder.

Conyers supplies a voice of caution in the WIRED piece, advising against over-relying on expensive machines for large-scale data collection if the people hoarding that data don’t necessarily know how to filter or interpret it.

[Image: Lawrence Conyers supervises two grad students using his ground-penetrating radar gear; photo by Geoff Manaugh.]

The goal of an International Subsurface Exploration Agency could rise or fall, in other words, not just on questions of funding or public support, but on the limits of software analysis and human interpretation: are we sure that what we see on the screens of our machines is actually there, underground?

When we spoke in Siena, Campana used the metaphor of a medical biopsy, insisting that archaeologists and geophysicists will always need to excavate, not just for the recovery of historical artifacts and materials, but for verifying their own hypotheses, literally testing the ground for things they think they’ve seen there.

Archaeologist Eileen Ernenwein, co-editor of the journal Archaeological Prospection, also emphasized this to me when I interviewed her for WIRED, adding a personal anecdote that has stuck with me. During her graduate thesis research, Ernenwein explained, she found magnetic evidence of severely eroded house walls at an indigenous site in New Mexico, but, after excavating to study them, realized that the structure was only visible in the electromagnetic data. It was no less physically real for only being visible magnetically—yet excavation alone would have almost certainly have missed the site altogether. She called it “the invisible house.”

In any case, many things have drawn me to this material, but the long-term electromagnetic traces of our built environment get very little discussion in architectural circles, and I would love this sort of legacy to be more prominently considered. What’s more, our cultural obsession with ruins will likely soon begin to absorb new sorts of images—such as radar blurs and magnetic signatures of invisible buildings—signaling an art historical shift in our representation of the architectural past.

For now, check out the WIRED article, if you get a chance.

(Thanks again to the Graham Foundation for Advanced Studies in the Fine Arts for supporting this research. Related: Through This Building Shines The Cosmos.)

Detecting lost rooms with architectural antennae

[Image: “Constant time slices” reveal buildings buried in northwestern Argentina; image from, and courtesy of, the Journal of Archaeological Science, “Detecting and mapping buried buildings with Ground-Penetrating Radar at an ancient village in northwestern Argentina,” by Néstor Bonomo, Ana Osella, and Norma Ratto].

While reading The Losers last night for the first time—a graphic novel about a team of ex-CIA members now executing a series of elaborate heists against their former employer—I was pleasantly surprised to see that one of the final scenarios involves a small volcanic island featuring an abandoned village that had very recently been buried by ash and pumice.

In a nutshell, the buildings beneath all that rock and ash are still intact—and one of them contains a locked safe that our eponymous group of “losers” is searching for. So begins an unfortunately quite short scene of vertical archaeology: locating the proper building amidst the featureless landscape of ash, blasting a hole down through the building’s roof, stabilizing the ceiling from within so that heavy-lifting equipment can be installed on the rooftop, and then descending into the hallways and staircases below by way of mountaineering ropes to find the safe.

For whatever reason, there are few things I find more exciting to read about than high-risk descents into buried cities, especially one that, as in the case of The Losers, remains otherwise indistinguishable from the surface of the earth, only gradually revealing itself to be an extraordinary honeycomb of connected rooms and passages—and this brief moment in the book was made even more interesting when I remembered a handful of articles I’d saved last year, one of which also involves a lost village, buried by volcanic ash.

[Image: A selection of “time slices” from the buried buildings of northwestern Argentina; image from, and courtesy of, the Journal of Archaeological Science, “Detecting and mapping buried buildings with Ground-Penetrating Radar at an ancient village in northwestern Argentina,” by Néstor Bonomo, Ana Osella, and Norma Ratto].

In a 1998 paper from the Journal of Applied Geophysics, called “The use of ground penetrating radar to map an ancient village buried by volcanic eruptions,” we read about a village in Japan called Komochi-mura, in Gunma prefecture: “The entire area surrounding the village is covered by a thick deposit of pumice derived from the eruption of Futatsudake volcano of Mt. Haruna, approximately 10km to the southwest of the village.”

Beneath the modern village, its predecessor from the middle of the 6th century is buried by the pumice deposits. Since these were laid down over a very short period, the ancient village should survive in a high state of preservation and will therefore contain much significant archaeological information. Ground penetrating radar (GPR) has been used to investigate this site over a period of 10 years. As a result, the plan of the ancient village can be accurately mapped… In this paper, the authors demonstrate how GPR was able to map the structural remains of the ancient village under a deposit of pumice.

In addition to various buildings, “pit-dwellings,” and other destroyed structures preserved but invisibly buried beneath today’s village, “traces of brushwood hedges, paths and other slight features have also been identified by the survey.”

These types of articles—on the remote-sensing of buried architectural remains, using technologies that “can detect and map buried structures without disturbing them,” in the words of the paper I am about to cite—are increasingly easy to find, but no less interesting because of their ubiquity.

Another paper, then, called “Detecting and mapping buried buildings with Ground-Penetrating Radar at an ancient village in northwestern Argentina,” published in 2010 in the Journal of Archaeological Science, describes an archaeological survey in which ground-penetrating radar was used “in order to detect new buildings,” including a system of “complex wall distribution and a number of unknown enclosures.” These “new buildings,” however, were just signals from the earth awaiting spatial interpretation:

The exploration showed signals of mud-walls in a sector that was located relatively far from the previously known buildings. A detailed survey was performed in this sector, and the results showed that the walls belonged to a large dwelling with several rooms. The discovery of this dwelling has considerably extended the size of the site, showing that the dwellings occupied at least twice the originally assumed area. High-density GPR surveys were acquired at different parts of the discovered building in order to resolve complex structures. Interpreted maps of the building were obtained.

“From the joint analysis of the transverse sections, time slices and volume slices of the data and their time averaged intensity,” the authors explain, “we have obtained a final map for the new building”—where the “new” building, of course, is a much older, forgotten one, a structure interpretively remade and refreshed through this newfound legibility.

[Image: From “Archaeological microgravimetric prospection inside don church (Valencia, Spain),” by Jorge Padín, Angel Martín, Ana Belén Anquela, in a 2012 issue of the Journal of Archaeological Science].

Architecture, in this context, comes to our attention first as a series of “intensity blots continued through consecutive slices,” an almost impossibly abstract geometry of signals and reflections, of patterned “electromagnetic responses” hidden in the landscape.

In all of these cases, it’d be interesting to propose a kind of archaeological discovery park the size of a football stadium, whose interior is simply a massive, open-span paved landscape on which small devices like floor-waxing machines or lawnmowers have been parked. Paying visitors can walk out onto this vast, continuous monument of bare concrete where they will begin moving the machines around, cautiously at first but then much more ambitiously, revealing as they do so the underground perimeters and outlines of entire villages buried deep in the mud and gravel beneath the building. The “park” is thus really a kind of terrestrial TV show of invisible architecture previously lost to history but beautifully preserved—that is, entombed—in the geology below.

In any case, in writing this post I’ve realized that I’ve accumulated over the past two years or so several gigabytes’ worth of PDFs about these and other archaeological technologies—from mapping ancient ships buried in the Egyptian pyramids and micro-gravity detection of “shallow subsurface structures” in a church in Italy (“indicating,” in the authors’ words, “that the actual church was constructed above another one”) to “archaeomagnetic data” taken from Roman sites in Tunisia—but here’s at least one more reference for good measure.

In a paper called “Ground penetrating radar (G.P.R.) surveys applied to the research of crypts in San Sebastiano’s church in Catania (Sicily),” from a 2007 issue of the Journal of Cultural Heritage, a team of Italian geophysicists explored “natural or anthropic buried cavities” under a church in Sicily—that is, both architectural chambers and caves physically inaccessible in the foundations of the building. Soon enough, the authors write, “the existence of hidden structures was revealed.”

“In fact,” they add, “a crypt with a barrel vault, under the central aisle of the church, and a room of small dimensions next to this crypt were identified. Moreover, near the altar, the presence of a quadrangular crypt with a cross-vault was revealed. The presence of such buried masonries confirms that the church, rebuilt on previous building rests, has been subjected along the centuries to repeated repairs.”

[Image: The church of San Sebastiano in Catania, Sicily, courtesy of the regional tourism council].

There is something particularly awesome—that is, it is a story that lends itself particularly to metaphor—about envisioning a squad of well-equipped scientists setting up shop in a church in Sicily, using radar and rigs of strange antennae to scan the structure around them for secret rooms, heavenly nooks and crannies out of human reach. A kind of electromagnetic baroque.

The paper cited in a caption above—”Archaeological microgravimetric prospection inside don church (Valencia, Spain),” by Jorge Padín, Angel Martín, Ana Belén Anquela, from a 2012 issue of the Journal of Archaeological Science—even includes such strangely resonant lines as calculating against “residual gravity anomalies” in a “microgravimetric correction for the altar,” as if the high science of geophysical investigation has been rhetorically wed with theological speculation.

In the words of a paper by N. Farnoosh et al., published in a 2008 issue of NDT & E International, analyzing a given architectural space becomes a question of “buried target detection” using high-tech means—that is, establishing a sustained and coordinated “electromagnetic interaction among the radar antennas, ground, and buried objects.”

Here, the study of architectural history can very, very loosely be compared to astronomy: using tools of remote-sensing, including antennae, but targeted downward, into the earth, to reveal the flickering, gossamer traces of something that, for a variety of reasons, humans can’t yet physically reach. Like astronomy, then, archaeology and architectural history become a case of interpreting signals from afar, not of stars and supernovae but of lost rooms and buildings beneath our feet.