17 December 2014
By Kerry Klein
Located about 25 miles north of Houston, Mueschke Cemetery is a historical burial ground. With its oldest headstone dating back to 1849, the cemetery is the resting place for close to 150 people, many of them soldiers killed in 150 years of American wars. But the cemetery is also known to contain dozens of unmarked graves, their locations lost over time. Now, a tool used by geologists and engineers is helping to find them: radar.
University of Houston graduate student Azie Aziz came to the cemetery armed with ground-penetrating radar (GPR), a geophysical technique that uses radar to image the Earth’s subsurface. A transmitter shoots rapid radar pulses into the ground, then a receiver detects the reflections after they refract along changes in the subsurface. Variations in return time help determine the shapes and sizes of underground objects.
As Aziz explained at a poster session Tuesday at the American Geophysical Union’s Fall Meeting in San Francisco, unmarked burials at Mueschke Cemetery aren’t all completely hidden. Some are indicated by sunken depressions in the ground or holes where headstones used to be. Others still have flowers from loved ones. Years ago, said Aziz, some families “used lilies planted on the surface to mark where the burial was because they didn’t have money to buy headstones.”
But challenges to locating the burials still loomed. The team anticipated the area’s clay-rich sediments wouldn’t transmit radar signals as well as other rock types. Only those bodies buried in cement vaults—generally those buried after the 1940s—would be easy to spot using the radar technique. Plus, this was a historical site, and the team was charged with not disturbing the land—a tall order for a lawnmower-sized unit that requires walking along tightly-spaced gridlines. “That’s another challenge working with a graveyard: it’s very sensitive,” said Aziz.
But after a series of surveys, Aziz said the team identified at least 10 likely burial sites. The findings show that GPR can be used effectively even where target objects aren’t clearly defined and where rock types may be problematic.
“In a lot of areas unfortunately, GPR has been looked at as being not as reliable as people want it to be,” said Jeffrey Solari, an engineer with 3D-Radar, a company that uses GPR for construction applications. “Seeing that there’s new applications coming out is very exciting.”
Because the area is historically sensitive, Aziz and her team aren’t permitted to dig down and test their findings. But they don’t need to: the Mueschke Cemetery Association has learned enough to know where to replace headstones and to create a more accurate tally of the burials at the site. For them, this might be the beginning of a new partnership.
“They want us to do more,” said Aziz.
Kerry Klein is a science communication graduate student at UC Santa Cruz.