Associate Professor Larry Conyers is one of the world's foremost experts in ground-penetrating radar. Photo: Wayne Armstrong
Larry Conyers wants archaeologists to stop digging. Seriously.
Conyers, an associate professor in DU’s Anthropology Department, is one of a handful of people in the world who specialize in using ground-penetrating radar (GPR) for archaeological research.
He’s used GPR to locate evidence of ancient civilizations, including temples, harbors and, two years ago, a shaft in a Peruvian pyramid containing the mummy of a tattooed woman who, according to a June 2006 National Geographic Magazine article, may have been an ancient Moche ruler or priestess.
He’s written and co-authored two definitive texts — Ground-Penetrating Radar: An Introduction for Archaeologists (Altamira Press, 1997) and Ground-Penetrating Radar for Archaeology (Altamira Press, 2004) — as well as dozens of book chapters and journal articles.
Conyers’ three-day intensive GPR course draws attendees from throughout the world. He’s also a much-sought after consultant, securing funded projects from the likes of Harvard University and the National Geographic Society that propel him and his students to far-flung locations including Israel, Jordan, Peru, Bolivia, Portugal and Tunisia.
So when Conyers claims his technology virtually eliminates the need to dig, people listen. That’s important, he says, because the archeological record is a finite resource.
“If you have to go dig up [archeological sites] to study them, you’re destroying them and they’re not being replaced,” he says.
Extracting artifacts takes them out of context, which Conyers believes can be a mistake.
“Much of a site is often dug up, put in a wheelbarrow and dumped,” Conyers says. “All many people collect are artifacts. But there’s much more an archeological site can tell you about the past.”
GPR techniques
Buried houses and garbage piles can reveal a lot through GPR, Conyers explains, noting that the technology allows study of sites before excavating.
And if excavation is going to take place, he says, GPR can direct archaeologists to the best spots to dig.
The process requires patience and precision. Conyers sets out a grid along which antennas — encased in a fiberglass box and hooked to a device that looks a lot like a weed eater on a bicycle wheel — transmit electromagnetic pulses into the ground. Those pulses or radio waves travel downwards in nanoseconds, the velocity changing as they encounter materials of different composition. A second antenna records the location and intensity of reflections from within the ground. When hundreds or thousands of reflections are processed in 3-D, their shape tells Conyers that something is buried or the ground has been disturbed.
GPR techniques grew out of seismic mapping exploration by the oil and gas industry, where Conyers first became acquainted with wave energy mapping. In recent years, computer-processing techniques developed for medical CAT scans, MRIs and sonograms have been modified to produce sub-surface images.
“This is very much a method that is the product of learning from people in a wide variety of high-tech research applications,” Conyers says.
Real world applications
Clark Davenport, a forensic geophysicist who regularly consults with the FBI and police departments around the country, worked with Conyers to locate a potential 19th century settler’s gravesite at the Rocky Mountain Arsenal.
“[Conyers] is a world renowned expert on GPR and specifically in the applications of GPR on archaeological sites,” Davenport says. “He is a rare breed of scientist in the sense that he is able to explain complicated matters in easily grasped terms, and his enthusiasm is contagious.”
Conyers has applied that enthusiasm to forensic research as well as archaeology, and has even helped a military group that searches for the remains of service members missing in action.
“Because it’s a relatively new science and there are so few of us doing it, I realized the need for broadening our data base,” he says. Ever eager to add to that knowledge base, Conyers took on his first cold case.
In March 2007 he traveled to San Luis Obispo, Calif., to search for the remains of Kristin Smart, a California Polytechnic State University freshman who has been missing since 1996.
Due to either poor decisions or bad luck, depending on who tells the story, the investigation into Smart’s disappearance got off to a rocky start. Cal Poly police initially thought Smart had run away, so they secured neither her room nor that of the freshman last seen with her — to date considered a “person of interest” in the case. Lacking evidence of foul play, investigators could do little more than chase clues and are still hoping for a break.
Conyers was able to lend his expertise to the Smart family legal team because of a civil suit filed by the suspect’s mother, who wants to stop Smart’s parents from alleging her son is involved in the disappearance. Because the suit allows the Smart family to obtain evidence to defend themselves, it was Conyers’ entree to search the suspect’s mother’s backyard, long rumored to have been Smart’s burial site.
The tiny yard’s surface was nearly entirely covered in concrete, but no matter. GPR can read through concrete like it’s onion paper.
Conyers laid out five grids throughout the L-shaped yard and in the adjacent garage. In two areas, he laid out a tighter grid and used a higher-resolution antenna for more detailed mapping.
Data collection is just the first step. It’s in the processing where Conyers’ expertise really shines. He ran the data from the backyard through a sophisticated DU-developed computer program that converts the reflected radar waves into vertical profiles and horizontal slices, which then reveal a three-dimensional view of whatever is underground. The maps are then rendered into colors where the more intense reflections appear as brightly colored shapes.
After reviewing his data, Conyers noted some “interesting anomalous features” — places investigators should focus their search. Conyers’ students reviewed the data and hit on the same features, including one that appeared to be head- and torso-shaped.
Intrigued by Conyers’ findings, in May crews excavated the suspicious areas but found no trace of Smart. Sometimes, Conyers says, a feature that resembles a body is simply a disturbance in the soil. Still, GPR does narrow the scope, eliminating some features and focusing on the most promising ones.
The future of GPR
For the past five years, DU students have been involved with GPR projects in Bolivia, Peru, Israel, and across the U.S. Conyers’ long list of projects includes a Harvard-funded stint in Israel this summer, which potentially could spawn some DU student master’s theses.
Some of his students are technologically competent enough for Conyers to send them out with the equipment to do their own research.
“It’s good for me because I get to be involved and learn from all of our students,” Conyers says.
Conyers believes the next generation of archaeologists will rely on the tools he’s used — antennas, computers and sophisticated software — to study buried objects and architecture.
But, he says, not all archaeologists are receptive to GPR technology. “We have people in the archeology community who are averse to what they perceive as complicated technology,” Conyers says. “Fortunately, a whole new generation of students isn’t intimidated by computer technology. This resonates with them in ways it often doesn’t with archaeologists of my generation.”