A theoretical relation between the celerity and trace velocity of infrasonic phases

et al. 2022

Preprint

Abstract. The International Monitoring System (IMS) has been established since the late 1990s for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The IMS is supposed to detect any explosion of at least 1 kt of TNT equivalent underground, underwater, and in the atmosphere. Upon completion, monitoring the Earth’s atmosphere for low-frequency pressure waves will be realized using up to 60 infrasound stations distributed over the globe. Acoustic waves in the infrasound range (between around 0.01 and 20 Hz) can efficiently propagate over long distances, subject to the winds near the stratopause at around 50 km. Therefore, infrasound observations of repeating or persistent sources have been suggested for probing the winds in the middle atmosphere, where numerical weather prediction models suffer from the lack of continuous observation technologies for data assimilation. One type of repetitive source is active volcanoes. In turn, this natural hazard for civil security can be monitored using infrasound, and first prototypes of applications for the release of early volcanic eruption warnings have been established. However, access to raw infrasound data or products of the IMS is limited to specific user groups, which might hinder the utilization of infrasound observations. In this study, we present advanced infrasound data products for atmospheric studies and civilian applications. For this purpose, 18 years of raw infrasound data (2003–2020) were reprocessed using the Progressive Multi-Channel Correlation method. A one-third octave frequency band configuration between 0.01 and 4 Hz was chosen for running this array-processing algorithm, which detects coherent infrasound waves within the background noise. From the comprehensive detection lists, each four products for 53 IMS infrasound stations were derived. The four products cover different frequency ranges and are provided at different temporal resolutions: a very low frequency set (0.02–0.07 Hz, 30 min; https://doi.org/10.25928/bgrseis_bblf-ifsd, Hupe et al., 2021a), two so-called microbarom frequency sets – covering both the lower (0.15–0.35 Hz, 15 min; https://doi.org/10.25928/bgrseis_mblf-ifsd, Hupe et al., 2021b) and a higher (0.45–0.65 Hz, 15 min; https://doi.org/10.25928/bgrseis_mbhf-ifsd, Hupe et al., 2021c) part – named after the dominant ambient noise of interacting ocean waves that is quasi-continuously detected at IMS stations, and observations with center frequencies of 1 to 3 Hz (5 min), called the high frequency product (https://doi.org/10.25928/bgrseis_bbhf-ifsd, Hupe et al., 2021d). Within these frequency ranges and time windows, the signals from the most dominant directions in terms of number of arrivals are summarized. Along with several detection parameters, calculated quantities for assessing the relative quality of the products are provided. The validity of the data products is demonstrated by diving into examples of recent events that produced infrasound detected at IMS infrasound stations, as well as a global assessment.

Section: Processing Resultsmentioning

confidence: 99%

Section: Data Processingmentioning

confidence: 99%

International Monitoring System infrasound data products for atmospheric studies and civilian applications

Hupe

Ceranna

et al. 2022

Preprint

“…Effectively raising the lower family size threshold from 10 to 40 and 50 ensures the global comparability of the stations' detection lists and any derived product in terms of this parameter, even though the ringing artifact did not affect all stations to the same extent. Notwithstanding the above, the apparent velocities must range between 300 and 500 m s −1 to be accepted as an infrasonic signature (e.g., Lonzaga, 2015). The availability of raw waveform data and processing results per station are shown, on a daily basis, in Fig.…”

Section: Data Processingmentioning

confidence: 99%

International Monitoring System infrasound data products for atmospheric studies and civilian applications

Hupe¹,

Ceranna²,

et al. 2022

Earth Syst. Sci. Data

Abstract. The International Monitoring System (IMS) was established in the late 1990s for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Upon completion, 60 infrasound stations distributed over the globe will monitor the Earth's atmosphere for low-frequency pressure waves. In this study, we present advanced infrasound data products of the 53 currently certified IMS infrasound stations for atmospheric studies and civilian applications. For this purpose, 18 years of raw IMS infrasound waveform data (2003–2020) were reprocessed using the Progressive Multi-Channel Correlation (PMCC) method. A one-third octave frequency band configuration between 0.01 and 4 Hz was chosen to run this array-processing algorithm which detects coherent infrasound waves within the background noise. From the comprehensive detection lists, four products were derived for each of the certified 53 IMS infrasound stations. The four products cover different frequency ranges and are provided at the following different temporal resolutions: a very low-frequency set (0.02–0.07 Hz, 30 min; https://doi.org/10.25928/bgrseis_bblf-ifsd, Hupe et al., 2021a), two so-called microbarom frequency sets – covering both the lower (0.15–0.35 Hz, 15 min; https://doi.org/10.25928/bgrseis_mblf-ifsd, Hupe et al., 2021b) and a higher (0.45–0.65 Hz, 15 min; https://doi.org/10.25928/bgrseis_mbhf-ifsd, Hupe et al., 2021c) part – named after the dominant ambient noise of interacting ocean waves that are quasi-continuously detected at IMS stations, and observations with center frequencies of 1 to 3 Hz (5 min), called the high-frequency product (https://doi.org/10.25928/bgrseis_bbhf-ifsd, Hupe et al., 2021d). Within these frequency ranges and time windows, the dominant repetitive signal directions are summarized. Along with several detection parameters, calculated quantities for assessing the relative quality of the products are provided. The validity of the data products is demonstrated through example case studies of recent events that produced infrasound detected at IMS infrasound stations and through a global assessment and summary of the products. The four infrasound data products cover globally repeating infrasound sources such as ocean ambient noise or persistently active volcanoes, which have previously been suggested as sources for probing the winds in the middle atmosphere. Therefore, our infrasound data products open up the IMS observations also to user groups who do not have unconstrained access to IMS data or who are unfamiliar with infrasound data processing using the PMCC method. These types of data products could potentially serve as a basis for volcanic eruption early warning systems in the future.

“…CC BY 4.0 License. of a microbarom signal from the Atlantic Ocean, with a back-azimuth of 225 • and a 350 m/s apparent velocity typical of the stratospheric regime (Garcés et al, 1998;Whitaker and Mutschlecner, 2008;Nippress et al, 2014;Lonzaga, 2015). The base resolution of the array was taken to be the 1-sigma beam width of the Gaussian fitted to the array response at a constant velocity 4 https://doi.org/10.5194/angeo-2020-78 Preprint.…”

Section: Infrasound Dataset and Signal Processingmentioning

confidence: 99%

“…In this study, classical linear vespa processing (Davies et al, 1971) is applied where the noise suppression is proportional to square root of N (Rost and Thomas, 2002). A beam is generated at each 1 • in back-azimuth, for the fixed apparent velocity of 350 m/s, which is within stratospheric arrival regime (Garcés et al, 1998;Whitaker and Mutschlecner, 2008;Nippress et al, 2014;Lonzaga, 2015). That allows to estimate signals coming from all directions but from approximately the same height corresponding to stratospheric altitudes.…”

Section: )mentioning

confidence: 99%

Microbarom radiation and propagation model assessment using infrasound recordings: a vespagram-based approach

Vorobeva

Carlo

et al. 2020

Preprint

Abstract. This study investigates the use of a vespagram-based approach as a tool for multi-directional comparison between simulated microbarom soundscapes and infrasound data recorded at ground-based array stations. Data recorded at the IS37 station in northern Norway during 2014–2019 have been processed to generate vespagrams (velocity spectral analysis) for five frequency bands between 0.1 and 0.6 Hz. The back-azimuth resolution between vespagrams and a microbarom model is harmonized by smoothing the modelled soundscapes along the back-azimuth axis with a kernel corresponding to the frequency-dependent array resolution. An estimate of similarity between the output of a microbarom radiation and propagation model and infrasound observations is then generated based on the image processing approach of mean-square difference. The analysis revealed that vespagrams can monitor seasonal variations in the microbarom azimuth distribution, amplitude, and frequency, as well as changes during sudden stratospheric warming. The vespagram-based approach is computationally inexpensive, can uncover microbarom source variability, and has potential for near-real-time stratospheric diagnostics and atmospheric model assessment.