Acoustic emissions from an industrial facility recorded during the TRANSAT stratospheric balloon flight

Human activity can create acoustic emissions capable of traveling many kilometers. Narrow band, “tonal” signatures are particularly distinct, as there are few processes in nature that produce them (e.g., volcanic tremor). Although stratospheric balloon flights over cities commonly record these signals, the plethora of emitters makes any single source difficult to distinguish. Acoustic sensors aboard the TRANSAT balloon flight from Sweden to Canada captured a multi-hour narrowband signal while crossing northern Norway. This distinct, isolated recording indicates a singular emitter capable of projecting sound nearly 40 km in the air and at least 100 km laterally. We describe the signal properties, calculate the detection range of the floating sensor, and constrain possible locations of the emission source. This is a first step towards the detection, characterization, and geolocation of narrowband acoustic signals from the stratosphere using a single free flying sensor. This has implications for characterizing anthropogenic activity on Earth as well as evaluating volcanic activity during proposed balloon missions to Venus.