Temporary Wind Noise Reduction Systems for Infrasound: Comparison Over Time and Response Analysis

Abstract:

Low frequency sound, less than 20 Hz and also known as infrasound, is produced by a variety of natural and anthropogenic sources. Monitoring these sources of interest is important for national security and hazard mitigation and requires recording high fidelity waveforms. However, the state of the atmosphere can make this difficult. Pressure fluctuations due to turbulence within the atmosphere (e.g. wind) are persistent sources of noise within the frequency band of infrasound. Robust wind noise reduction methods for the International Monitoring System (IMS) infrasound stations have been extensively studied, but such systems are not ideal for temporary deployments due to cost and effort. Porous hoses are still common in temporary infrasound deployments despite being recommended against ten years ago. The response of porous hoses is unknown, and signals have been shown to be either attenuated or amplified depending on their backazimuth, incidence angle, and frequency content. Even with this previous research, infrasound wind noise reduction systems for fast, light, and inexpensive deployments continue to include porous hoses. Other wind noise reduction systems like porous wind domes and fences have shown promise in reducing wind noise while keeping waveform fidelity. While there has never been a publication explicitly recommending the placement of a bucket over an infrasound sensor, this method is occasionally used, often is not explicitly noted in publications, and only anecdotal evidence exists as to how this system performs. Studies have yet to investigate these temporary wind noise reduction system responses over time. This research compares three temporary wind noise reduction systems for infrasound sensors. We present a comparison of (1) wind noise reduction and (2) waveform shape for three systems as well as (3) analyze the responses of the systems over time and (4) compute a transfer function that can be applied to the porous hose system.

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