Mitigation of infrasound noise on stratospheric solar powered balloons

Infrasound is described as low frequency pressure waves that are below the threshold for human hearing (< 20 Hz). Due to their low attenuation, these waves can travel thousands of kilometers which allows for the remote sensing of seismic events, a known source of infrasound. Earthquakes are seismic events that can be monitored through stratospheric solar powered balloons, termed heliotropes, that float in the upper stratosphere. The balloon carries two sensors and floats along the path of the local winds where there is minimal relative speed between it and the local air. The sensors must be separated some distance to accurately resolve the direction of any incoming signal. The added separation between them increases the relative speed on the lower sensor, thereby generating excess wind noise. Identifying one method of wind noise reduction for the balloons here on Earth can translate to recording quakes via balloon-based infrasound sensors on the interior of other planets like Venus. Due to its extreme surface temperatures (~ 460 °C) and pressures (~ 90 atm), there are no direct seismic measurements on the surface of Venus. However, Venus has a much less severe middle atmosphere where the balloons could be deployed. The current work reports on various windscreen designs, their ground-based testing, and the flight tests of the windscreens on the balloons.