A Bird’s‐Eye View on Ambient Infrasonic Soundscapes

• Published in: Geophysical research letters Vol. 48; no. 17
• Main Authors: den Ouden, Olivier F. C., Smets, Pieter S. M., Assink, Jelle D., Evers, Läslo G.
• Format: Journal Article
• Language: English
• Published: 16-09-2021
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094555

A method is introduced to reconstruct microbarom soundscapes in absolute values. The soundscapes are compared to remote infrasound recordings from infrasound array I23FR (Kerguelen Island) and in situ recordings by the INFRA‐EAR, a biologger deployed near the Crozet Islands. The reconstruction method accounts for all‐acoustic contributions, divided into evanescent microbaroms (detectable directly above the source) and propagating microbaroms (detectable over long ranges). It is computed by integrating acoustic intensities over the ocean surface, convolved with the transfer function quantifying the propagation losses and propagation time. The reconstructed soundscapes are found within 2.7 dB for 85% of the measurements in the microbarom band of 0.1–0.3 Hz. Infrasonic soundscapes are essential for understanding the ambient infrasonic noise field and are a basic need for applications, such as atmospheric remote sensing, natural hazard monitoring, and verification of the Comprehensive Nuclear‐Test‐Ban Treaty.
Plain Language Summary
Microbaroms are omnipresent sources of low‐frequency, inaudible sound, that is, infrasound. They have a characteristic and continuous signature within the infrasound spectrum and are often classified as ambient noise. The microbarom signals can be divided into a direct signal, only detectable close by the source, and a propagating signal, which travels over large distances. Under noisy conditions, microbaroms can mask infrasonic signals of interest, such as infrasound from volcanoes or explosions. Insights in the ambient noise field improve natural hazards monitoring and the verification of the Comprehensive Nuclear‐Test‐Ban Treaty. In this study, a method for the reconstruction of the microbarom source field is introduced. The method reconstructs omnidirectional soundscapes in absolute numbers. This is a significant improvement to previous approaches, which accounted for the normalized loudest source region only. The reconstructed soundscapes are compared with microbarom recordings by microbarometer arrays and the INFRA‐EAR, a miniature sensor deployed as a biologger near the Crozet Islands. The comparison shows a statistical agreement for 85% of the time between the modeled and observed soundscapes.
Key Points
Evanescent microbaroms and propagating microbaroms are measured on an infrasound bio‐logger fitted to a Wandering Albatross
A method is developed to reconstruct omnidirectional microbarom soundscapes in absolute values, which can account for both microbarom fields
The method is used to quantify the probabilistic microbarom exposure of microbarometers