Fidelity of infrasound measurements with balloon-borne sensorsa)

Deploying acoustic sensors on free-flying, long-living balloons helps to reach the areas not accessible with the traditional ground-based sensors, reduce flow noise, and improve characterization of various infrasound sources. Instrumented balloons can potentially increase the infrasonic detection range and early warning lead time for natural hazards. Balloons are also considered as platforms for planetary exploration. When assessing the capabilities of balloon-borne infrasonic sensors and interpreting the measurements, it is imperative to recognize that the balloon inevitably distorts the signals and background infrasound field by scattering the incoming sound. This paper quantifies the effects of hot-air and helium balloons on acoustic pressure and particle acceleration and the role of balloon skin in infrasound diffraction. It is found that balloon-borne vector sensors are more susceptible to distortions than pressure sensors, leading to major differences between the apparent and true source bearing and directionality.