A high-tech look into the past

On a typical day, you find Allen Gontz, an assistant professor of environmental, earth, and ocean sciences, of coastal geology at UMass Boston, in historic neighborhoods of Boston pulling an electronically equipped skid plate along the surface of the ground, directing waves of radar deep down.

"What we are looking for is historical and cultural objects or remnants," he said. "It could help develop a better understanding of what Boston would have looked like during the Revolutionary War."

First and foremost a scientist, Gontz is spearheading the use of surveying systems and software that non-invasively, non-destructively map the subsurface and the features within it.

His latest examination is of the grounds of the Paul Revere House, Boston's oldest building and a historic Colonial landmark. There, surveyors from the Boston firm Harry R. Feldman Inc. are teaming up with Gontz to create a digital picture of what's above and below ground so history can be protected as the space is enlarged.

The organization that runs the Paul Revere House the Paul Revere Memorial Association aims to expand its historic North End site to include a neighboring residence Revere once owned, creating more space for the thousands of visitors each year who make the pilgrimage each year to a starting point of the American Revolution. Although the Revere house was built in 1680, no thorough land survey has ever been done. If the team is able to locate the foundations, preservation groups can restore the property to the way it looked in the 1700s, when Revere began delivering messages for the American revolutionaries.

"This gives us a way to do things without digging," Nina Zannieri, executive director of the Paul Revere Memorial Association said according to the Boston Globe. "It’s a heavily visited site. We had 255,000 visitors last year. It’s a major historical site."

Gontz jumped at the chance to bring his students to study the Revere site when the association approached him. His focus is on the city's original coastline, and the Paul Revere House was originally only two streets from Boston Harbor.

Although the data from the recent surveys are still being analyzed, based on preliminary readings the UMass team suspects that a privy - a gold mine for historical researchers for what it reveals about the lives and habits of those who used it - and other foundations or walls, revealing structures now long forgotten, will be discovered.

Feldman employees and the UMass group are now working with their images, cleaning them up and creating a virtually perfect computerized three dimensional image of the property. Using medical imaging software, they will produce an image that can be rotated and viewed on a computer screen. Precise dimensions of the building will be available, and an exact record of the historic property is established for posterity.

Gontz’s methods work by sending a tiny pulse of energy into a material and recording the strength and the time required for the return of any reflected signal. A series of pulses over a single area make up what is called a scan. Reflections are produced whenever the energy pulse enters into a material with different electrical conduction properties the material it left. The strength of the reflection is determined by the contrast of the two materials. This means that a pulse which moves from dry sand to wet sand will produce a very strong, brilliantly visible reflection, while one moving from dry sand to limestone will produce a very weak reflections.

Data are collected in parallel transects and then placed together in their appropriate locations for computer processing in a specialized software program. The computer then produces a horizontal surface at a particular depth in the record. This is referred to as a depth slice, which allows operators to interpret a plan view of the survey area.

In recent years, the use of these non-invasive techniques has transformed earth science. The emerging field draws on scholars in computer science, mathematics and statistics, classical studies, architecture, geography, graphic arts and design, and physical anthropology. The resulting methods reduce the cost, time and risk associated with archaeological investigations.

The innovation in the Paul Revere House examination is figuring out how to stitch together the images. "It's really cutting-edge work anywhere in the world,” according to Gontz.