Capturing the sounds of the stratosphere using solar hot air balloons

Low frequency sounds can travel vast distances across the planet, carrying information about the events that generated them as well as the medium through which they travel. These sounds are usually recorded on surface-based sensors. Recently, however, sensors have been lofted on high altitude balloons, where they have revealed a rich soundscape quite different than that of the Earth’s surface. Here we describe acoustic observations of the lower stratosphere conducted using inexpensive microbarometers lofted via passive solar hot air balloons. We discuss background noise as well as individual events, some of whose origins remain enigmatic. We delve into how to carry out an acoustic sensing mission using our instrumentation and flight system. Finally, we outline future directions for this technology, including deployment on extraterrestrial bodies such as Venus. [SNL is managed and operated by NTESS under DOE NNSA under Contract No. DE-NA000352.]