Origin and mitigation of wind noise on balloon-borne infrasound microbarometers

[Infrasound - implications for human medicine]

Infrasound describes ubiquitous, low-frequency sound (< 20 Hz) in the environment with a long wavelength below the median hearing threshold, which can nevertheless be heard and tactilely perceived, depending on the sound pressure level and frequency spectrum. In nature, infrasound emissions usually occur only in the low-threshold range. Nevertheless, after strong and chronic exposure to usually artificially generated infrasound emissions, various effects on the ear and the body, sometimes questionably critical to health, can be observed. Correct measurement and assessment of infrasound sources is complex and controversial. Established guidelines are scarce. Innovative research areas include infrasound monitoring for evaluation of natural events and infrasound applications in medicine. In the future, it is hoped that new insights will be gained from infrasound research and that a more extensive classification in occupational medicine will be possible.

Infrasound direction of arrival determination using a balloon-borne aeroseismometer

Free-floating balloons are an emerging platform for infrasound recording, but they cannot host arrays sufficiently wide for multi-sensor acoustic direction finding techniques. Because infrasound waves are longitudinal, the balloon motion in response to acoustic loading can be used to determine the signal azimuth. This technique, called "aeroseismometry," permits sparse balloon-borne networks to geolocate acoustic sources. This is demonstrated by using an aeroseismometer on a stratospheric balloon to measure the direction of arrival of acoustic waves from successive ground chemical explosions. A geolocation algorithm adapted from hydroacoustics is then used to calculate the location of the explosions.

The First Detection of an Earthquake From a Balloon Using Its Acoustic Signature

Extreme temperature and pressure conditions on the surface of Venus present formidable technological challenges against performing ground-based seismology. Efficient coupling between the Venusian atmosphere and the solid planet theoretically allows the study of seismically generated acoustic waves using balloons in the upper atmosphere, where conditions are far more clement. However, earthquake detection from a balloon has never been demonstrated. We present the first detection of an earthquake from a balloon-borne microbarometer near Ridgecrest, CA in July 2019 and include a detailed analysis of the dependence of seismic infrasound, as measured from a balloon on earthquake source parameters, topography, and crustal and atmospheric structure. Our comprehensive analysis of seismo-acoustic phenomenology demonstrates that seismic activity is detectable from a high-altitude platform on Earth, and that Rayleigh wave-induced infrasound can be used to constrain subsurface velocities, paving the way for the detection and characterization of such signals on Venus.