Imagine being able to "hear" a tornado before the National Weather service ever sees it on radar. Or a volcano before a catastrophic eruption. Or potentially treacherous clear air turbulence long before a passenger jet ever flies through it.
That may sound like the stuff of a Superman comic, but Qamar Shams and Allan Zuckerwar, two researchers from NASA's Langley Research Center in Hampton, Virginia, have developed a technology they think is capable of doing all those things — and more.
In fact, their invention, the Extreme Low Frequency Acoustic Measurement System, recently won NASA's Commercial Invention of the Year award for 2013.
The system works by detecting infrasound, or sound waves at frequencies below 20 hertz. Sounds at those frequencies are inaudible to the human ear. The system also reduces the effect of ambient winds.
An important characteristic of infrasonic sound is that it travels long distances. Shams uses a severe thunderstorm to illustrate this phenomenon.
"If there's a thunderstorm here," he says, referring to Hampton, "people who live in Williamsburg and Gloucester may not be able to hear it." That's because sounds in the average person's hearing range, between 20 and 20,000 hertz, are absorbed after traveling just a few kilometers.
However, Shams explains, if the same thunderstorm is emitting infrasonic signals, that sound could travel thousands of miles. A frequency of .01 hertz can travel around the circumference of the Earth.
But what use is infrasound if we can't hear it?
That's where the Extreme Low Frequency Acoustic Measurement System comes in. Infrasonic sound is emitted by many natural and man-made phenomena, including tornadoes, clear air turbulence, nuclear explosions and the wake vortices created by airplanes.
There are clear advantages to being able to detect those kinds of phenomena from a distance. It's something researchers have been working on since the 1960s.
In fact, infrasonic detection technology already existed before Zuckerwar and Shams developed their system. But those technologies tended to be excessively large, taking up space the size of an athletic field. They use extensive hose systems to filter out wind noise, but the hoses are ineffective if winds get beyond a certain speed.
The Extreme Low Frequency Acoustic Measurement System eliminates the size and wind-noise problems. It's compact, employing a small microphone specially designed to capture infrasound. In addition, instead of using long, unwieldy hoses to filter out wind noise, it uses a specially designed windscreen, which does the job very effectively and has the added advantage of being waterproof, thus an all-weather system. The windscreen is not an off-the-shelf item but is manufactured locally. The system has netted excellent results in the field for Zuckerwar and Shams.
"We have picked up unprecedented low background level signals," Shams said. "Those low-level signals were beyond the reach of prior technologies."
Zuckerwar and Shams envision a host of potential uses for their invention.
Measurements in the field reveal that it is capable of detecting clear air turbulence. According to Shams, clear air turbulence costs the aviation industry almost $100 million annually. Pilots often have to descend or reroute because of the turbulence, which is caused, for example, by the jet stream. It can also cause structural damage to aircraft.
With an infrasonic detection system in place to "hear" the turbulence earlier, Shams believes the industry could alleviate some of those costs.
"They could make a plan to avoid the clear air turbulence," he said. "There would be less pollution, less fuel burn, less structural damage and passengers would feel more comfortable, less inconvenienced."
Similarly, the industry could use the system to detect wake vortices, the turbulence that forms behind an aircraft as it passes through the air. Aircraft have to maintain set distances from one another because of the vortices, but according to Zuckerwar and Shams those distances are often overly conservative.Wake vortices produce an infrasonic signature. If pilots and air traffic controllers could detect the vortices, Shams says, they could safely reduce the spacing between aircraft.
The system could also be used to detect natural disasters. Scientists at the University of Oklahoma have approached Zuckerwar and Shams about installing a system in Oklahoma to detect tornadoes.
Shams believes an infrasound-based detection system would be advantageous over radar because it may "hear" a tornado's infrasonic signatures as it was forming. "We can have a system to provide enough warning to residents about where tornadoes are forming and in which direction the spiral wind is moving," he said.
Shams and Zuckerwar also believe their system could possibly be useful in the detection of earthquakes, tsunamis and volcanic eruptions, but they currently don’t have substantiating data. They are looking at opportunities for collection of data to verify the concept.
The technology could have medical applications as well. Researchers at NASA's Kennedy Space Center are testing an infrasonic stethoscope that's been modified to record data from the human heart. In the infrasonic region there may be sounds valuable to a physician that can’t be heard with or recorded using a traditional stethoscope.
There's even been talk of sending microphones to Mars to detect dust devils, which could pose a threat to astronauts when humans eventually set foot on the Red Planet.
Putting microphones on Mars is wishful thinking for now, though. Shams and Zuckerwar are just happy to have won the award.
In an email, Zuckerwar said much credit has to go to those who supported the development of the technology, which began in 2006:
"Innovation at a place like Langley Research Center requires the support of many people employed by the center, both civil service and contractors. My first feelings were those of gratitude for the level of support that we received from our managers and colleagues."
Shams hopes that winning the award will help get word out about their invention.
"Now it's time to take this out and tell people what we have, what the applications are, and let us prove that these systems are capable of doing all those things we expect," he said.
NASA Langley Research Center