A look into the past, with laser precision

Scientists and surveyors team up to catalogue every inch of the Paul Revere site, above and below ground

The organization that runs the Paul Revere House aims to expand its historic North End site to include a neighboring property Revere once owned, creating more space for school groups and the thousands of others who make the pilgrimage each year to the starting point of one of the American Revolution's best-known episodes.

But before the nonprofit association that oversees the property can renovate the former residences at Lathrop Place, install an elevator to accommodate those with disabilities, or connect the two properties through an existing brick wall, executives want to catalogue every inch of the one-fifth-acre site - above and below the surface.

Doing that will involve marrying three-dimensional laser surveying techniques with the work of a geologist and budding environmental scientists from the University of Massachusetts at Boston.

In the process, researchers hope to learn things they never knew about one of the Boston tourism industry's jewels.

The project started when the Paul Revere Memorial Association began planning to make additions and improvements to the site as its 100 anniversary approached this year. After the association purchased Lathrop House for $1 million, Nina Zannieri, executive director, wanted to know how the planned changes would affect what is above the surface - and what might be underground.

Although the Revere house was built in 1680, no thorough land survey has ever been done.

Now surveyors from the Boston firm Harry R. Feldman Inc. and an academic team from UMass Boston are collaborating to create a three-dimensional digital picture of the house and associated structures, the garden where water was once drawn from a hand-dug well, and even what's below ground, down to about 10 feet.

A picture of what's above the surface, created by the Feldman firm using a laser scanner, is being stitched together electronically with a radar-generated image of what's underground produced by the UMass Boston team, so history - even the remains of a privy - can be protected as the space is enlarged.

"You've got the building in its entirety," said Stephen M. Wilkes, director of 3-D services at Feldman, as he projected an image of the property that looked more like a color photographic negative than a picture. "You can plan to the nth degree."

Allen Gontz, assistant professor of coastal geology and geophysics at UMass-Boston, jumped at the chance to bring his students to study the Revere site when Zannieri approached him. His focus is on the city's original coastline, and the Paul Revere House was originally only two streets from Boston Harbor.

Gontz's team spent six days pulling an electronically equipped "skid plate" along the surface of the ground, directing waves of radar deep down. Those bounced back and were recorded, revealing anomalies - "hot spots" - in the layers of earth and sediment.

In 1983, a privy - a gold mine for historical researchers for what it reveals about the lives and habits of those who used it - was found under the 1711 Pierce/Hichborn House, another historic structure on the Revere association's property.

Although the data from the recent surveys are still being analyzed, based on preliminary readings the UMass team suspects that another privy and other foundations or walls, revealing structures now long forgotten, will be discovered.

Gontz compared an underground area that has never been disturbed to "a seven-layer chocolate tort," with layers of soil or sediment or sand instead of cake icing. If the chef got hungry, Gontz explained, "and dug the center out to eat it, and then filled it with something else" - well, that's how the evidence of a privy or old well might look, surrounded by undisturbed material.

Zannieri is interested in knowing where, for example, she can place the foundation for a new elevator without disturbing an old cobblestone walkway that once connected the two buildings.

"I can give her an idea," he said. "A lot of it is interpretation and looking at how things relate to each other." That will determine where alterations can be made to the property, and it will identify spots that city and state archeologists might want to explore.

Revere's house marks the start of the journey he made to warn other patriot leaders that the British were planning to march on Lexington and Concord, setting the stage for the first armed conflict of the American Revolution.

Over the years, the Paul Revere House has been a wealthy merchant's home, an artisan's residence, a rooming house, and a tenement with shops. It was renovated in 1907 and opened to visitors a year later.

Paul Revere, the great-great-great grandson of the silversmith and patriot, is chairman of the association's board.

The house is the oldest in what was originally Boston, though not the oldest in Boston as it exists today. Revere lived there in four rooms, an attic, and a basement with some of his 16 children from two wives, as he prospered in the silver, iron, and copper businesses.

Zannieri said the board hopes to raise money and perhaps use a modest portion of its endowment to renovate the new property. "We have such a high demand, particularly for summer and after-school programs, that we need additional space," she said.

The site has about 250,000 visitors annually.

A few months after the UMass group got started, Michael A. Feldman, president of the surveying company and a Boston history buff, called Zannieri. He wanted to choose a couple of historic sites in Boston and offer them professional surveys free of charge. "I wanted to give back," said Feldman, who has done large developments like the W Hotel being built in the Theatre District and a planned South Station office tower.

His timing couldn't have been better.

"It was the most beautiful thing," said Zannieri. "I said it just so happens we need a boundary survey done."

Feldman told her about the 3-D scanning he does, and she told him about the below-ground radar search that was already being conducted. "He said, 'Oh wow.' At that point the technology guys got together, and that was the last I saw of them."

What was originally to be a standard ground survey turned into five days of laser scanning and conventional survey work - some 23 million laser dots, about 1/16 of inch in size, recorded digitally from five angles. The work includes valuable data that can be used by architects and contractors, but it also produced colorful, surrealistic-looking images of the existing structures.

"The scanned images Michael is doing, they're art," said Zannieri. "They're really cool."

Feldman employees and the UMass group are now working with their images, cleaning them up and creating a virtually perfect computerized image of the property. Using medical imaging software, the same technology that helps produce pictures of unborn babies, 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.

Some version of the data that is produced may even show up on the Paul Revere House's website. "Nina will be able to produce animation or a walk-through tour," Feldman said.

The final and hardest task is stitching together the images from below ground and the laser picture from above. "The integration of laser scan data and GPR data is a very new thing," Wilkes said. "It's really cutting-edge work anywhere in the world, let alone archeology and engineering.

And it's good for anybody interested in Boston's past.

"I love it when we can say to the public all these things mesh together," Zannieri said. "The history, the geography, the science, the technology."

Thomas C. Palmer Jr. can be reached at tpalmer@globe.com.