It’s all about that bass and lots of it. Deep, deep base—sound at frequencies too low for the human ear to pick-up.
It’s called infrasound, low-frequency soundwaves formed by events as diverse as ocean waves crashing together, volcanic eruptions and earthquakes to rocket launches. These soundwaves, capable of traveling around the world multiple times, have never been recorded from the stratosphere for more than a day and a half and never over the ocean. That is, not until this past year.
NASA’s 2016 Super Pressure Balloon flight from Wanaka, New Zealand, carried the Compton Spectrometer and Imager (COSI) payload, a gamma ray telescope. Tucked behind one of COSI’s solar panels was the Carolina Infrasound instrument, a three-kilogram payload resembling a small styrofoam ice chest on the outside but with a trio of InfraBSU infrasound microphones on the inside. A Boise State University team led by Associate Professor Jeff Johnson originally designed the microphones to record volcanic explosions, but the sensors have found an unexpected new use in the stratosphere.