Acoustic Waves From a Distant Explosion Recorded on a Continuously Ascending Balloon in the Middle Stratosphere

A helium‐filled mylar balloon carrying a smartphone and infrasound sensors ascended to a stratospheric height of 35 km over the surface detonation of a chemical explosive, with a total acoustic propagation distance of 127 km. The smartphone was configured to collect multi‐modal data at high rates from internal sensors. Analysis of the data shows successful collection of the explosion signal by both the smartphone's microphone and its accelerometers, the first from an ascending balloon. Comparison of the acoustic signal with that collected by other infrasound sensors, both airborne and ground‐based, provides insight into the possibilities and limitations of collecting acoustic data from the stratosphere. Plain Language Summary A surface chemical explosion was observed by pressure and acceleration sensors suspended from an ascending free‐floating balloon at a height of 35 km and a total propagation distance of 127 km from the blast. The balloon's sensor package included a smartphone collecting different types of data (including audio, acceleration, and position), as well as more traditional infrasound and location sensors. The explosion signal was observed by the airborne pressure and vertical accelerometer sensors, as well as by surface‐deployed traditional and smartphone pressure and acceleration sensors. The blast signatures recorded by the airborne and ground‐based stations are compared to provide insight into the present capabilities, limitations, and possible improvements to future balloon‐borne collections of seismo‐acoustic signatures on Earth and beyond. Key Points Explosion signals were captured using acoustic sensors in an ascending balloon at a height of 35 km and a propagation distance of 127 km The signal was briefly trapped in the troposphere before escaping into the stratosphere Accelerometers can distinguish acoustic signals from wind noise on ascending balloons