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

Inexpensive 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 just took painter’s plastic, masking tape, a dash of coal dust, and plenty of sunlight.

Daniel Bowman of Sandia National Laboratories presented his findings on using solar-powered hot air balloons to eavesdrop on stratospheric sounds at the 184th meeting of the Acoustical Society of America.

The stratosphere is a relatively calm layer of Earth’s atmosphere. Rarely disturbed by aircraft or turbulence, microphones in the stratosphere pick up a variety of sounds unheard anywhere else. This includes natural sounds from the crash of ocean waves and thunder, human-made sounds such as wind turbines or explosions, and even sounds of unknown origins.

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

To get into the stratosphere, Bowman and his collaborators make balloons that stretch 6 to 7 meters. Despite their large size and data-gathering ability, balloons are relatively simple to make.

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

The researchers collect data and detect low-frequency sound using micrometers, which were originally designed to monitor volcanoes. After the balloons are released, they trace their paths using[{” 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,] “There are mysterious ultrasound signals happening a few times an hour on some flights, but their source is not entirely known,” Bowman said.

Solar-powered balloons can also help explore other planets, such as observing[{” attribute=””>كوكب الزهرةالنشاط الزلزالي والبركاني من خلال غلافه الجوي السميك.

الاجتماع: اجتماع ASA 184