Flight Testing of Infrasound Windscreen on Stratospheric Solar Powered Balloons

Infrasound is acoustic pressure waves at frequencies below the threshold of human hearing (< 20 Hz). Due to their low frequency, these waves can travel thousands of kilometers with minimal attenuation. This makes infrasound a compelling method for remote sensing of seismic events. While most infrasound monitoring is done on the ground, recent work using stratospheric solar powered balloons has enabled low-cost airborne infrasound monitoring. These balloons float in the lower stratosphere (~ 20 km) and generate lift by using solar radiation to heat the air within its envelope. One application of this technology is seismic monitoring on Venus. However, to resolve the direction of arrival, at least two payloads must be on the same flight line with a separation distance on the order of the infrasound wavelength. Since balloons move with local winds, there is typically minimal relative wind between the balloon and the air, but drag from the long flight line will increase the relative wind speed on the lower payload, and thus wind noise. On Venus, this will be amplified by extreme wind shear within its atmosphere. Previous work tested different windscreen configurations and evaluated them based on their ability to suppress wind noise without attenuation of coherent signals. Ground testing identified a combination of dense foam and canvas material as the most effective method for compact windscreens. This presentation will focus on sensitivity to inlet configurations as well as evaluation of flight tested windscreens.