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 using solar-powered hot air balloons to eavesdrop on stratospheric sounds in 184th Meeting of the Acoustical Society of America On Thursday, May 11th.
The stratosphere is a relatively calm layer of Earth’s atmosphere. Microphones in the stratosphere are rarely disturbed by aircraft or turbulence, and 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.
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 it becomes buoyant. 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 track their routes using GPS—a necessary task because balloons sometimes sail for hundreds of miles and land in hard-to-reach places. But because balloons are inexpensive and easy to set up and launch, they can launch a lot more balloons and collect more data.
Besides the expected human and environmental sounds, Bowman and his team discovered something they could not identify.
“(In the stratosphere) there are mysterious ultrasound signals happening a few times an hour on some flights, but their source is completely unknown,” Bowman said.
Solar-powered balloons could also aid exploration of other planets, such as observing the seismic and volcanic activity of Venus through its thick atmosphere.
the quote: Solar-Powered Balloons Detect Mysterious Sounds in the Stratosphere (2023, May 11) Retrieved May 11, 2023 from https://phys.org/news/2023-05-solar-powered-balloons-mysterious-stratosphere.html
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