Abstract
Thirty infrasound sensors have been operated over Japan since 2015. We developed the irregular array data processing in order to detect and estimate the parameters of the arrival source waves by using infrasound data related to the sequence of the volcanic eruption at Mt. Shinmoedake in March 2018. We found that the apparent velocity at the ground was equal to the acoustic velocity at particular reflection levels. The results were confirmed through a comparison of the findings of the apparent velocity with a wave propagation simulation on the basis of the azimuth, infrasound time arrivals, and the state of the atmospheric background using global atmospheric models. In addition, simple ideas for estimating horizontal wind speeds at certain atmospheric altitudes based on infrasound observation data and their validation and comparison were presented. The calculated upper wind speed and wind observed by radiosonde measurements were found to have a qualitative agreement. Propagation modeling for these events estimated celerities in the propagation direction to the sensors that were consistent with the tropospheric and stratospheric ducting. This study could inspire writers, in particular, and readers, in general, to take advantage of the benefits of infrasound wave remote-sensing for the study of the Earth’s atmospheric dynamics.
Highlights
Infrasound is classified as sound waves with frequencies below the normal limit of human hearing and is often cited as the frequency range 0.02–10 Hz [1]
(2) At stations located on the mountain slope, such as stations KUT05 (Figure 7d), Kochi University of Technology (KUT) 01 (Figure 7a), and KUT02 (Figure 7b), mountain winds mostly affected the characteristics of the recorded data as infrasonic pressure anomalies
Station KUT07 was selected as a sample for the examination of daily power spectral density (PSD) variations because it was more responsive to the changes in spectral variations of the received signals
Summary
Infrasound is classified as sound waves with frequencies below the normal limit of human hearing and is often cited as the frequency range 0.02–10 Hz [1]. These waves are generated from various human-made and natural sources and can propagate efficiently over regional and global scales of thousands of kilometers, with low intrinsic attenuation [2,3]. Since the observation network was established, our sensors have successfully detected and recorded several natural phenomena that produced infrasound waves (e.g., explosive volcanic eruptions and an intense earthquake that occurred in Japan).
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