Solar-powered balloons detect mysterious sounds of unknown origin in Earth’s stratosphere


Daniel Bowman of Sandia National Laboratories uses inexpensive solar-powered hot air balloons to discover unique sounds in the stratosphere. This technology can be used to explore other planets.

Cheap and easy to build, these data-gathering balloons pick up low-frequency sound in Earth’s atmosphere.

Imagine if sending your science experiment 70,000 feet in the air had spilled painter’s plastic, duct tape, a little bit of coal dust, and lots of sunlight.

Daniel Bowman of Sandia National Laboratories presented his findings on using solar-powered hot air balloons to listen to sounds of the stratosphere at the 184th meeting of the American Acoustic Society.

The stratosphere is the relatively quiet layer of Earth’s atmosphere. Rarely disturbed by aircraft or turbulence, microphones in the stratosphere pick up a wide range of sounds that are not heard anywhere else. These include natural sounds of crashing ocean waves and thunder, man-made sounds such as wind turbines or explosions, and sounds of unknown origin.

Solar hot air balloon with infrared microbarometer payload

Inflating a solar hot air balloon with an infrared microbarometer payload. Credit: Darielle Dexheimer, Sandia National Laboratories


To reach the stratosphere, Bowman and his collaborators build balloons 6 to 7 meters high. Despite their large size and potential for data collection, ballooning is relatively simple.


“Our balloons are giant plastic bags with some charcoal dust inside to darken them. We make them using painter’s plastic from the hardware store and shipping tape and charcoal powder from fireworks supply stores. When sunlight hits the dark balloons, it heats the air inside. “This passive solar energy is enough to bring the balloons up to 20 km (66,000 ft) above the surface,” Bowman said. “Each balloon requires only $50 worth of materials and can be built into a basketball court.”

The researchers collect data and detect the low-frequency sound using micrometers, which were originally designed to monitor volcanoes. After the balloons are released, they retrace their tracks[{” attribute=””>GPS – a necessary task since the balloons sometimes sail for hundreds of miles and land in hard-to-reach places. But, because the balloons are inexpensive and easy to construct and launch, they can release a lot of balloons and collect more data.

Along with the expected human and environmental sounds, Bowman and his team detected something they are not able to identify.

“[In the stratosphere,] “Some planes have mysterious infrared signals a few times an hour, but their source is completely unknown,” Bowman said.

Solar-powered balloons can also aid in exploration of other planets, i.e. observing[{”attribute=””>Venus’seismicandvolcanicactivitythroughitsthickatmosphere[{”attribute=””>Venus’seismicandvolcanicactivitythroughitsthickatmosphere

Meeting: ASA 184th Meeting