Army studies city sounds to help soldiers hear threats

When Donald Albert and Stephen Decato came to Baltimore from rural New Hampshire to sample the urban noise environment for the Army, they had two worries.

How dangerous would it be to work on streets they'd seen portrayed in bloody HBO crime dramas?

And what kind of suspicion might they arouse as they deployed their black attache cases and weird electronic equipment in a city that was reliving a nightmare during the trial of Washington-area sniper John Allen Mohammad?

They found out quickly, Albert told a meeting of the American Acoustical Society in Baltimore this week. Soon after they set up their sensors at a light rail station in Linthicum, somebody turned in the two scientists.

"We were there a full two minutes before Officer Mooney drove up on the sidewalk and questioned us, with his right hand on his gun," Albert recalled.

They were not arrested, nor were they accosted by criminals. And Albert was able to report to fellow scientists this week that the research here in May 2006 should help the military design sound and seismic sensors that can distinguish between threatening noise and vibrations and the mostly harmless cacophony of an urban environment.

The investigation was spurred by the changing nature of the challenges facing today's military.

"The Army has traditionally done all of its testing and development in [proving grounds in] White Sands [N.M.], or Yuma [Ariz.] — places like that that are big open areas," he said. "But the Army is fighting in urban areas. And in the future they want their equipment to be able to work in urban areas."

The acoustical systems that the Army uses to help soldiers detect vehicle movement, footsteps or sniper fire must be able to distinguish those sounds from the din of diesel trucks and motorbikes and construction at similar frequencies.

Albert once asked an Army lieutenant colonel in Baghdad what soldiers hear most when they're on patrol in the urban streets of Iraq.

"He thought about it for a minute, and he said, ‘Generators,'" Albert recalled. Repeated power outages have made diesel generators ubiquitous in Iraq. "We made some measurements of generators so we can include that in our models, because that's what these guys are hearing."

Filtering out that noise might enable sensors to more easily detect the sniper shots soldiers often don't hear before someone is hit.

But much more data is needed to assemble a comprehensive understanding of the urban noise environment. And that's where Baltimore came in.

Albert and Decato, his longtime research technician, work for the Army's Cold Regions Research and Engineering Laboratory, located in bucolic — and quiet — Hanover, N.H. Other projects have required them to haul their equipment out among the wolves and bears in Alaska; for this work, they needed to head for a city.

Albert chose Baltimore because "it's easy to get around. We rode the light rail and walked around. It's big enough that it … had tall buildings. And it was relatively cheap to get here."

It also happens to be the site of other long-term studies of the urban environment that might one day benefit from environmental noise data.

He acknowledged that he had trepidations, mostly those of a self-described "country boy" who has read and seen plenty —fictional and real — about crime in Baltimore.

"I get chased by turkeys every morning when I go for a walk. That's the kind of environment I'm in," he said. Baltimore "is different."

In the end, he said, "we were glad we didn't get shot, we didn't get mugged and we didn't get arrested, especially. I loved the city. We enjoyed being here."

Over the course of a week, they went to 10 places in and around Baltimore. At each one, they set up their microphone to sample sounds and a "geophone" to measure vibrations in the ground too faint for humans to sense. For 30 minutes at each stop, they took a series of one-minute readings, averaging loudness of the sounds at various frequencies or wavelengths.

"We didn't record. We couldn't tell if somebody was saying something," Albert said. "We were looking for what the overall level is, which frequencies were high and which frequencies were low. … This is a really basic study, our first study at these frequencies."

As they sampled the noise on Calvert, Lombard and other downtown streets, Baltimoreans looked at them with suspicion and curiosity; some asked what they were up to. After a while, Albert and Decato found a way to avoid notice.

"They don't pay attention to you if you're standing by a bus stop," Albert said. And the researchers were judicious about taking photos that might arouse anger or suspicion. They stood across the street from each other, Albert said, "so he could come and bail me out."

They went to a street of rowhouses, and to Federal Hill to try to capture the noise of the harbor and construction along Key Highway. And they sampled the sounds of the rail yards and port activity in Locust Point.

Much of what they heard was normal street noise — sirens, horns, car and truck traffic, footsteps, conversation. As might be expected, it was louder downtown than on the residential street. Overall, they found less industrial noise in Baltimore than they had expected. Some of that, he suggested, might be the result of years of federal workplace noise regulation. Some might be due to the loss of industry.

"Traffic noise was dominant acoustically. … It overwhelmed the jackhammers and cranes," Albert said. And the general noise levels were 10 to 50 times louder than those they recorded, for a baseline, in rural Pomfret, Vt. Vibration levels were 10 to 500 times stronger.

Some of what they measured was well below the range of human hearing. But it all needs to be characterized, Albert said, so that sensors and computer models can be designed to sort it out for soldiers. More work is needed to learn to decode the paths of sounds echoing around corners in urban canyons. And it will take more samples like these to characterize the noises in other places.

"This is an American city, and that's all it is," Albert said. "If you go somewhere else, you'll have different vehicle codes, vehicles without mufflers, motorcycles. … The signature of the noise is going to change depending on where you are."

Albert says he hopes that his work will have broad applications.

"Noise is becoming a larger and larger problem," he said. "People's health is affected by noise, and we need to know what it is and how to mitigate or reduce it in some way. I think in the future it's going to get bigger and bigger."

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