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Back to the Stratosphere

It’s been half a century since scientists tried to go up high to hear low-frequency sound. Danny Bowman, an unusually curious geophysicist, is intrigued by the implications.


Story and photos by Mary Lide Parker ’11

“It might not work. It might not take off, or it might crash a few feet off the ground — but you’re welcome to come watch.”

Danny Bowman and his colleague Xiao Yang

When you can’t get out to the desert, the parking lot behind Mitchell Hall will do. Danny Bowman and his colleague Xiao Yang launch a homemade balloon —- from a plastic paint drop cloth — that will snag on a building, catch a breeze and rise to 72,000 feet. That’s where it will find infrasound waves, which can’t be heard down here.

Danny Bowman, a doctoral student in geological sciences at UNC, is not a pessimist, but he has launched enough balloons over the years to know that things do not always go as planned. In high school, he and his friends launched a balloon, constructed from a trash bag and birthday candles, that flew 30 feet before landing in a tree and starting a fire. He has learned a lot in the 15 years since that first launch — so much that he’s even worked with NASA — but, like any good scientist, he is always skeptical of his own design and engineering.

bowman_danny IMG_2360_MLPIt is a warm, sunny morning in the parking lot behind Mitchell Hall. I have my camera, and Bowman has what looks like an enormous trash bag spread out on the ground. It’s a solar balloon that he and his colleague Xiao Yang made from a plastic paint drop cloth. Bowman picks up one end of it and slowly starts jogging in circles.

Ten minutes later, the 19-foot homemade balloon is inflated and bobbing slowly up and down. Bowman holds it above his head, then spreads his arms wide to release it. The massive balloon slowly floats up, up — and into the corner of the brick building in front of us. For a few agonizing seconds, it looks like it might be stuck.

“Come on,” Bowman mutters. “Come on …”

And then, with help from the slightest breeze, the balloon detaches from the building and continues to glide upward. A minute later, it is hundreds of feet above us.

“The best thing ever is to build something with your own hands,” Bowman says with a smile, still staring up at it. “And then it flies.”

Now it’s just a white speck in the Carolina blue sky. Over the next two hours, it will soar up to 72,000 feet.

Not since the ’60s

Building and launching solar balloons is more than just a fun challenge for Bowman — it’s a fundamental part of his doctoral research at UNC. As a geophysicist, he specializes in recording infrasound in the stratosphere. In much the same way that his seismologist colleagues track seismic waves to map the inner parts of the Earth, Bowman uses infrasound waves to glean information about the Earth’s surface and atmosphere.

This is not your typical PhD research. The last time scientists measured infrasound in the stratosphere was in the 1960s.

“For the first time in half a century, we’re gaining access to a region of the atmosphere that hasn’t been directly observed in sound waves,” Bowman said. “The instruments we send into the stratosphere measure rapid changes in pressure. So if a sound wave goes by, the pressure fluctuates and that produces a signal which we record on our data loggers. And low-frequency sound travels a long way.”

Bowman compares it to a car driving by, thumping a loud sound system. “You tend to hear the bass notes, but not the treble notes. The same is true in the atmosphere.”

The “bass notes” produced by storms, ocean waves, volcanic eruptions and earthquakes can travel great distances — and they carry energy.

“So if you know how many sound waves are going up, you can calculate how much heat that’s generating in the upper atmosphere.” That heat energy could have consequences for satellites. The United Nations uses low-frequency sound measurements to enforce the Comprehensive Nuclear Test Ban Treaty. In the future, this technology could help the military record clandestine nuclear blasts.

Stratospheric infrasound measurements also could help detect small meteors and asteroids entering Earth’s atmosphere — some of which are too small to be picked up by traditional ground-based means. After a meteor exploded over Chelyabinsk, Russia, in early 2013, researchers became much more interested in methods for detecting smaller space fragments. The Southwest Research Institute in Colorado is in the process of launching an initiative to do just that, using the same approach as Bowman.

“They haven’t flown yet, but they’re going to,” he said.

Bowman’s technology ultimately enables him to record signals that don’t necessarily make it to the ground and signals that happen very far away — so far that he can record ocean sounds from the desert.

Balloon Launch Slideshow

 

A tiny airport (and NASA)

In the southeastern corner of New Mexico, just outside the tiny town of Fort Sumner, is a small municipal airport. The quiet tract has just one runway and a few buildings, surrounded by a lot of flat, dry desert. Most of the year, this remote piece of land sees very little activity. But on a clear morning in early September, the place is buzzing with energy — dozens of engineers and scientists hard at work.

This little airport in the middle of nowhere also is a NASA base for high-altitude balloon launches.

Every September, the Columbia Scientific Balloon Facility team, along with science students from universities across the country, descends upon Fort Sumner to launch research experiments into the stratosphere. Bowman, along with his friend and colleague Jake Anderson ’09, is among them. Bowman has spent six months planning, designing and building payloads that can house and protect his infrasound microphones as they ride along on the High Altitude Student Platform flight. All of the students go through a rigorous application and testing process to have their experiments accepted to fly 25 miles into the sky. In the 10 years that the HASP program has been running, Bowman is the first researcher from UNC to qualify.

Bowman and Anderson, now a doctoral candidate in geosciences at Boise State University, haul their equipment into the desert. They set up a ground array that will measure some of the same infrasound signals as the equipment on the balloon. Having two data sets will be helpful when Bowman sits down to analyze the data later.

The sun is high and blindingly bright, and the earth is dry and hot. A salamander slithers by, and Bowman says to keep an eye out for rattlesnakes. But he isn’t fazed by the harsh desert conditions. It reminds him of home. He grew up just three hours from here in Socorro. His dad also was a geologist.

“When you live in the desert, you have to make your own fun,” Bowman said. He and his daredevil friends were good at it — they built and launched their first homemade balloon in high school. “We used balsa wood, birthday candles and trash bags. And probably Scotch tape or super glue or something. It was really flimsy.

“It was clear that improvements could be made. Including the launch location. From then on, being the cool kids that we were, our weekends were spent building and flying things like this.”


‘The best thing ever is to build something with your own hands. And then it flies.’


Now, it’s serious business. For one thing, balloons and their payloads are subject to regulations, such as the ones emerging for drones — Bowman is liable for any damages they could cause.

He always checks and double-checks the winds, but still there is a degree of risk. Once the balloon is up, there is always a chance it could go off course.

“What are the winds doing up there?” Bowman asks Gregory Guzik, the director of HASP.

“Still blowing east to west,” Guzik says. “We won’t see the turnaround until next Wednesday.”

Winds in the stratosphere change direction — or “turn around” — twice a year, in the fall and spring. In the summer, the stratospheric winds blow from east to west. In the fall, typically in September, they switch. On Sept. 5, the winds haven’t switched yet. The launch is scheduled for two days hence. If all goes well, the balloon will fly to an altitude of about 120,000 feet, float a couple hundred miles west and come down north of Flagstaff, Ariz.

It goes like clockwork. Launch day begins at 3 a.m. There is a lot of coffee 
and not a lot of small talk. Everyone focuses on the job at hand, systematically running through checklists. By 5 a.m., the team rolls the gondola out of the hangar. At 7 a.m., the engineers begin to inflate the 500-foot balloon with helium. The total suspended weight beneath the balloon is about 2,000 pounds. The balloon itself, fully inflated, can fill an average football stadium. To launch the thing, atmospheric conditions need to be perfect.

It could be called off at any time. At 8 a.m., it’s a go.

The balloon takes off and, within 30 minutes, the colossal structure looks like a white dot 25 miles high in the sky. All of the instrumentation in the payload is powered by lithium batteries. Using radio signals, the Columbia Scientific Balloon Facility team tracks the instrumentation on board the balloon. Everything is running as it should be. But one thing is off: The balloon isn’t following the predicted flight pattern. It’s hovering directly above the airport.

It turns out the turnaround occurred early. Now, there are a few days of no wind at all. The balloon stays in one place.

This is unexpected good news for Bowman and the other researchers. If it had flown west to Arizona, the engineers would have brought the balloon down that evening — before it could float into Los Angeles airspace. But if it’s hovering over Fort Sumner, the balloon can stay up overnight, allowing Bowman’s microphones and data loggers to collect many more hours of data.

I’ll build it myself

After participating in two HASP launches, plus launching his own solar balloon and a weather balloon, Bowman has accumulated about 30 hours of data from the stratosphere, and he is constantly working through what it all means. Analyzing infrasound signals is a bit like cracking a top-secret code, and Bowman is committed to the decoding. He needs more data, though. He needs to do more balloon launches. This science is in its infancy.

“I don’t want to have to fund hundreds of thousands of dollars for a professional balloon launch. I want to do it myself.” While his own balloon launches always will be higher-risk than an operation like HASP, Bowman hopes to refine his expertise enough to make them an “acceptable” level of risk.

Bowman holds the tether

Bowman holds the tether before the Thanksgiving Day launch. This weather balloon reached 93,000 feet, and Bowman accurately predicted the trajectory and landing location — and he got all his instrumentation back intact.

On a bitter-cold morning the day before Thanksgiving, he launched a weather balloon that flew to 93,000 feet. Bowman accurately predicted the flight trajectory and the landing location, and all the instrumentation remained intact — successful, and the first of its kind.

“As far as I know, no one has ever put an infrasound sensor on a weather balloon before,” Bowman said.

What happens next? Upload the data and plan for the next launch.

As yet, just a glimmer

When he’s not constructing balloons or poring over his data, Bowman searches the Internet for people doing similar things. It turns out there are lots of amateur balloon builders out there — their successful launches (and failures) are scattered across message boards, blogs and YouTube. Like any passionate community of people, they encourage each other to keep sending objects into the sky.

“It’s hard to believe that an ordinary person can send a camera a third of the way to space. Just that idea keeps us going.”

But for all the avid balloon builders out there, Bowman stands alone in the realm of high-altitude infrasound work. The last scientific literature he can find on this subject, from the early 1960s, was published when not only the technology but the environment was different.

Bowman speculates that this type of research hasn’t been done in 50 years, mainly due to lack of funding and a large disconnect between the scientific ballooning community and the infrasound community. In a way, Bowman’s research, funded by the National Science Foundation, fills a large gap.

The data he has collected during the two HASP flights are entirely different from any sort of existing infrasound measurements — even those taken back in the early 1960s. Technology has progressed exponentially in the past half-century, and the soundscape is completely different now.

At this point, Bowman describes his understanding of infrasound in the stratosphere as just a glimmer — the bright tip of the iceberg. He wants to put more brain power behind it. “I want to build up enough research to get other people involved. There are so many different areas of expertise that could be brought to this — any one person could never cover a fraction of the potential that might exist.”

With more research and more scientists, Bowman hopes that 10 or 20 years from now he’ll be able to look at his spectrogram and identify every single waveform — a complete cracking of the code. “I want to look at it and fully understand it. But right now, some of these things — we just have no idea.”

Once he and his colleagues gain a more comprehensive understanding of all the different signals, Bowman wants to take his research farther into space. “The dream would be to take it to another planet — to fly these microphones on Venus or Jupiter, and do the same thing. I hear Pluto has an atmosphere.”

Mary Lide Parker ’11 is a writer, photographer and video producer at UNC whose work mainly appears in Endeavors, Carolina’s online research magazine.

Danny Bowman talks about and shows off his work.
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