Infrasound Waves Research Articles

Microbarometer measurements to probe turbulent kinetic energy in the atmospheric boundary layer

Microbarometer networks are typically in place for the detection of atmospheric infrasound waves. The monitoring of such waves can be of interest for source characterization, which include a wide array of geophysical and man-made sources, as well as atmospheric infrasound propagation studies. In such studies, the presence of turbulence and other wind-induced effects are considered a nuisance. For this reason, wind noise filters are typically in place for suppression. As Cuxart et al. [BLM (2013)] pointed out, microbarometer measurements indeed have a value for detection of local and remote turbulence and measurements can be used to estimate turbulent kinetic energy (TKE). In this study, we compare microbarometer observations at the Cabauw atmospheric research site to co-located in-situ TKE measurements. Moreover, we compare turbulence timeseries to predictions from the high-resolution HARMONIE weather model in which this quantity is parameterized. This approach has two foreseen applications: (1) modeled TKE fields could possibly help in identifying regions that are most appropriate for infrasound monitoring due to low TKE values and (2) microbarometer observations could possibly be of use in the further refining of the modeled TKE parameter.

Disturbances in the Ionosphere That Accompanied Typhoon Activity in the Vicinity of China in September 2019

AbstractWe have acquired HF Doppler measurements and studied the dynamics of the ionosphere in the ∼100–300 km altitude range during the 1–10 September 2019 period of typhoon activity near the People's Republic of China (PRC). The multifrequency multiple path system located at the Harbin Engineering University campus, the PRC, and probing the ionosphere at oblique incidence was used to identify the effects from the typhoons. The response of the ionosphere to the Typhoon Lingling was detected along three adjacent radio‐wave propagation paths where chaotic and quasiperiodic variations in the Doppler shift and a significant (from −1 to 1 Hz or greater) Doppler spectrum broadening were observed to occur. The Doppler spectrum chaotic variations are due to plasma turbulence generated by typhoons in the ionosphere, and the Doppler shift quasiperiodic variations along the main ray are due to infrasound and atmospheric gravity waves (AGWs) launched by the typhoons. The relative amplitude of quasiperiodic variations in the electron density in the field of the infrasound wave reached several percent, and in the field of the AGW attained from ten to a few tens of percent. The effects of the Typhoon Faxai during 9/10 and 10/11 September 2019 nights were accompanied by a 27% decrease in the electron density in the ionospheric E and F regions. At the closest approach of the Typhoon Faxai to the ionosonde during 8/9 September 2019 night, when it had the largest energy, a 56% increase was detected in the ionospheric F region electron density.

Topographically Scattered Infrasound Waves Observed on Microbarometer Arrays in the Lower Stratosphere

AbstractWhen an acoustic wave strikes a topographic feature, some of its energy is scattered. Sensors on the ground cannot capture these scattered signals when they propagate at high angles. We report observations of upwardly‐scattered acoustic waves prior to refraction back to the ground, intercepting them with a set of balloon‐borne infrasound microbarometers in the lower stratosphere over northern Sweden. We show that these scattered waves generate a coda whose presence can be related to topography beneath balloons and low‐altitude acoustic ducts. The inclination of the coda signals changes systematically with time, as expected from waves arriving from scatterers successively closer to receivers. The codas are present when a temperature inversion channels infrasound from a set of ground chemical explosions along the ground, but are absent following the inversion's dissipation. Since scattering partitions energy away from the main arrival, these observations imply a mechanism of amplitude loss that had previously been inaccessible to measurement. As such, these data and results allow for a better comprehension of interactions between atmospheric infrasound propagation and the solid earth.

Method of studying infrasound waves from thunderstorms гл

The paper provides an overview of studies of infrasound signals from thunderstorms over a period of more than 30 years. We deal with several types of infrasound signals from thunderstorms detected at the ISTP SB RAS infrasound station Badary in Buryatia. Special attention is paid to signals arising during the rarefaction phase. A mechanism for generating signals of this type by converting the energy of the electrostatic field into fluctuations in the pressure field was proposed by Dessler in 1973. We propose a method for identifying thunderstorm infrasound signals of various types: 1 — signals from an expanding thermal lightning channel; 2 — signals with an electrostatic generation mechanism. Using infrasound signals recorded earlier at the station in Buryatia as an example, we discuss the validity of the thunderstorm cloud model and assess some parameters of the thunderstorm source of infrasound.

Infrasonic, Acoustic and Seismic Waves Produced by the Axion Quark Nuggets

We advocate the idea that Axion Quark Nuggets (AQN) hitting the Earth can be detected by analysing the infrasound, acoustic, and seismic waves which always accompany their passage in the atmosphere and underground. Our estimates for the infrasonic frequency ν≃5 Hz and overpressure δp∼0.3 Pa for relatively large size dark matter (DM) nuggets suggest that sensitivity of presently available instruments is already sufficient to detect very intense (but very rare) events today with existing technology. A study of much more frequent but less intense events requires a new type of instrument. We propose a detection strategy for a systematic study to search for such relatively weak and frequent events by using distributed acoustic sensing and briefly mention other possible detection methods.

Infrasound–Electric‐Field Coupling Associated With the 2018 Shinmoe‐Dake Eruptions, Kirishima Volcanic Complex, Japan

Shinmoe-dake volcano, which is within the Kirishima volcanic complex, Japan, erupted from March to June 2018. The eruptions were recorded by various geophysical instruments that were installed 3.1–5.4 km from the crater. Here we present the first documented evidence of infrasound-induced electric-field changes in the near surface at the time of the explosive eruptions. Significant electric-field changes coincide with the infrasound arrivals. An order-of-magnitude estimation of the electric field indicates that the electrokinetic mechanism induced by pore water movement relative to the host rock, is a plausible cause of the observed infrasound–electric-field coupling. The ground displacement and electric-field particle motions suggest that the infrasound waves from the explosive eruptions produce vertical ground motion, and simultaneously induce horizontal groundwater flow, which subsequently generates electric-field changes due to the propagation of the infrasound wave.

Leak Localization of Gas Pipeline Based on the Combination of EEMD and Cross-Spectrum Analysis

Pipeline transportation systems play an increasingly essential role in the development of the economy. An accurate location of leakage is important to reduce economic losses and maintain the safe operation of pipelines. In this article, a pipeline leakage detection method based on infrasound and negative pressure waves (NPWs) is adopted. This method can locate the leakage only by collecting the infrasound and pressure signals at the first station of the pipeline, which effectively solves the disadvantages of low positioning accuracy of a signal and easily produces false alarms. In this article, the signal denoising method of cross-spectral analysis combined with ensemble empirical mode decomposition (EEMD) was adopted. First, the leakage signals of sound waves and NPWs are processed by EEMD to obtain a series of intrinsic mode functions (IMFs). The characteristic frequency band is obtained by cross-spectral analysis of the leakage signal. Within this frequency band, the dominant component of the leakage source signal is divided by correlation analysis, and the IMF component is reconstructed to complete the signal denoising. When compared to the single signal pipeline leak detection method, the positioning accuracy of this article showed a 1–3 m improvement on average.

Topographically Scattered Infrasound Waves Observed on Microbarometer Arrays in the Lower Stratosphere

Topographically Scattered Infrasound Waves Observed on Microbarometer Arrays in the Lower Stratosphere

Detection of acoustic wave generated by Baganuur mining explosion

We analyzed all available recorded infrasound data and determined the station detection capability in Mongolia. While in the winter times, we continuously detect acoustic signals from blasts at the Baganuur open-pit mine (150 km from infrasound I34MN station), which we rarely registered during the summer times. A previous study has shown that the noise level increased by 5 dB - 10 dB in the summer, which affected the detection capability of the stations. On the other hand, this could be connected to infrasound propagation model difference between winter and summer times. To verify this phenomenon, we installed a new infrasound IBHM station in a forest area at a distance of 350 km from the Baganuur mine area. When we compared the background noise level of the two stations, the noise level at the temporary station was lower than the permanent one, which allowed us to compare winter and summer time registered infra wave characteristics. With the comparison observed and modeled, apparent velocity suggested that winter and summer time detection difference could be due to the propagation model of infrasound wave itself.

Illuminating the North Korean nuclear explosion test in 2017 using remote infrasound observations

SUMMARYNorth Korea conducted its sixth underground nuclear explosion test (${m_\mathrm{ b}}$ 6.3) on 2017 September 3. The underground explosion produced substantial low-frequency atmospheric waves, which were detected by infrasound arrays located up to a distance of 566 km. These infrasound waves are formed by the conversion of seismic energy to acoustic energy across the lithosphere–atmosphere interface. While infrasound records at regional distances produce estimates of ground motion amplitude over spatially extended regions covering about 26 500 km2, 3-D full seismo-acoustic simulations within the lithosphere and atmosphere provide quantitative information about seismo-acoustic energy partitioning. Our results demonstrate the capability of remote infrasound observations combined with 3-D propagation modelling to further develop discrimination methods for underground sources. These results contribute to enhance the confidence of source identification and characterization in nuclear test monitoring research, which is essential for the enforcement of the Comprehensive Nuclear-Test-Ban Treaty.

Seismo-acoustic characterisation of the 2018 Ambae (Manaro Voui) eruption, Vanuatu

A new episode of unrest and phreatic/phreatomagmatic/magmatic eruptions occurred at Ambae volcano, Vanuatu, in 2017–2018. We installed a multi-station seismo-acoustic network consisting of seven 3-component broadband seismic stations and four 3-element (26–62 m maximum inter-element separation) infrasound arrays during the last phase of the 2018 eruption episode, capturing at least six reported major explosions towards the end of the eruption episode. The observed volcanic seismic signals are generally in the passband 0.5–10 Hz during the eruptive activity, but the corresponding acoustic signals have relatively low frequencies (< 1 Hz). Apparent very-long-period (< 0.2 Hz) seismic signals are also observed during the eruptive episode, but we show that they are generated as ground-coupled airwaves and propagate with atmospheric acoustic velocity. We observe strongly coherent infrasound waves at all acoustic arrays during the eruptions. Using waveform similarity of the acoustic signals, we detect previously unreported volcanic explosions at the summit vent region based on constant-celerity reverse-time-migration (RTM) analysis. The detected acoustic bursts are temporally related to shallow seismic volcanic tremor (frequency content of 5–10 Hz), which we characterise using a simplified amplitude ratio method at a seismic station pair with different distances from the vent. The amplitude ratio increased at the onset of large explosions and then decreased, which is interpreted as the seismic source ascent and descent. The ratio change is potentially useful to recognise volcanic unrest using only two seismic stations quickly. This study reiterates the value of joint seismo-acoustic data for improving interpretation of volcanic activity and reducing ambiguity in geophysical monitoring.

Assimilating atmospheric infrasound data to constrain atmospheric winds in a two‐dimensional grid

AbstractInfrasound waves travelling through atmospheric channels are affected by the conditions they encounter along their path. The shift in the back azimuth angle of a wavefront detected at the reception site depends on the cross‐winds it encountered. Estimating the original field from this integrated measurement is an (ill‐posed) inverse problem. By using a prior, this can be converted into a Bayesian estimation problem. In this work, we use the (ensemble) Kalman filter (EnKF) to tackle this problem. In particular, we provide an illustration of the setup and solution of the problem in a two‐dimensional grid, depending on both across‐track distance and height, which has not been done in previous works. We use a synthetic setup to discuss the details of the method. We show that one of the effects of along‐track averaging (done in previous studies to simplify the problem) is to overestimate the magnitude of the analysed values, and propose that this will be a source of model error. We also illustrate the process with real data corresponding to nine controlled ammunition explosions that took place in the summer of 2018. In these cases, the real infrasound waves we study seldom reach higher than km in height. However, the use of covariance‐based methods (e.g., the EnKF) allows for updates in higher regions where the wave did not travel and where traditional observations are sparse. In fact, the larger impacts from observations in these cases are in the region of 40–60 km, in agreement with previous works. This study contributes to paving the way towards the ultimate goal of assimilating information derived from infrasound waves into operational numerical weather forecasting. More studies in quality control of the observations and proper validation of the results are urgently needed.

SPECFEM2D-DG, an open-source software modelling mechanical waves in coupled solid–fluid systems: the linearized Navier–Stokes approach

SUMMARYWe introduce SPECFEM2D-DG, an open-source, time-domain, hybrid Galerkin software modelling the propagation of seismic and acoustic waves in coupled solid–fluid systems. For the solid part, the visco-elastic system from the routinely used SPECFEM2D software is used to simulate linear seismic waves subject to attenuation. For the fluid part, SPECFEM2D-DG includes two extensions to the acoustic part of SPECFEM2D, both relying on the Navier–Stokes equations to model high-frequency acoustics, infrasound and gravity waves in complex atmospheres. The first fluid extension, SPECFEM2D-DG-FNS, was introduced in 2017 by Brissaud, Martin, Garcia, and Komatitsch; it features a nonlinear Full Navier–Stokes (FNS) approach discretized with a discontinuous Galerkin numerical scheme. In this contribution, we focus only on introducing a second fluid extension, SPECFEM2D-DG-LNS, based on the same numerical method but rather relying on the Linear Navier–Stokes (LNS) equations. The three main modules of SPECFEM2D-DG all use the spectral element method (SEM). For both fluid extensions (FNS and LNS), two-way mechanical coupling conditions preserve the Riemann problem solution at the fluid–solid interface. Absorbing outer boundary conditions (ABCs) derived from the perfectly matched layers’ approach is proposed for the LNS extension. The SEM approach supports complex topographies and unstructured meshes. The LNS equations allow the use of range-dependent atmospheric models, known to be crucial for the propagation of infrasound at regional scales. The LNS extension is verified using the method of manufactured solutions, and convergence is numerically characterized. The mechanical coupling conditions at the fluid–solid interface (between the LNS and elastodynamics systems of equations) are verified against theoretical reflection-transmission coefficients. The ABCs in the LNS extension are tested and prove to yield satisfactory energy dissipation. In an example case study, we model infrasonic waves caused by quakes occurring under various topographies; we characterize the acoustic scattering conditions as well as the apparent acoustic radiation pattern. Finally, we discuss the example case and conclude by describing the capabilities of this software. SPECFEM2D-DG is open-source and is freely available online on GitHub.

Numerical Modeling of Infrasound Energy Radiation by Debris Flow Events

Debris flows constitute a severe natural hazard in Alpine regions. Studies are performed to understand the event predictability and to identify early warning systems and procedures. These are based both on sensors deployed along the channels or on the amplitude of seismic and infrasound waves radiated by the flow and recorded far away. Despite being very promising, infrasound cannot be used to infer the source characteristics due to the lack of a physical model of the infrasound energy radiated by debris flows. Here the simulation of water flow along a simple channel is presented, experiencing the fall from a dam, performed within the open source simulation code OpenFOAM. The pressure perturbation within the atmosphere produced by the flow is extracted and the infrasound signature of the events as a function of the flow characteristics is defined. Numerical results suggest that infrasound is radiated immediately downstream of the dam with amplitude and period that scale with dam height and water level. Modeled infrasound waveform is interpreted as being produced mostly by waves at the water free surface developing downstream of the dam. Despite the effect of sediments is not considered in this first study and will be implemented in future investigations, numerical results obtained with this simple model are in general agreement with experimental results obtained from array analysis of infrasound data recorded at Illgraben, Switzerland. Results highlight how numerical modeling can provide critical information to define a source mechanism of infrasound energy radiation by debris-flow, that is required also to improve early warning systems.

Hilbert-Huang transform of infrasound for tsunami early warning systems

When an earthquake occurs tectonically and volcanically, it is preceded by the emergence of sound wave propagation that cannot be heard by the human ear because it has a low frequency, called infrasound. These infrasound waves are difficult to detect because they are much weaker than earthquake waves and other natural sound waves in nature. The Hilbert-Huang transform method (HHT) is proposed, which in principle decomposes a wave into several simpler sinusoidal harmonic waves so as to separate the low-frequency infrasound waves from the other waves. Once separated, the envelope frequency can be determined which represents the frequency of the earthquake occurrence, then the amplitude represents the predicted earthquake strength, and the wave propagation phase that represents the location of the earthquake source. From the comparison of secondary data, it was obtained that HHT was able to obtain all three information faster than the data from seismographs so that it had the potential to increase the evacuation time which in turn reduced the potential for greater casualties and losses.

Infrasonic Earthquake Detectability Investigated in Southern Part of Japan, 2019.

The Kochi University of Technology (KUT) Infrasound Sensor Network contains 30 infrasound sensors which are distributed all over Japan especially in Shikoku Island. At all infrasound stations installed with three-axis accelerometers to measure the peak ground acceleration (PGA). Many earthquakes were detected by our system after establishing of the network since 2016. In this study we will focus on all the possibilities for infrasound detection generated from earthquakes using KUT sensor network and International Monitoring system (IMS) stations for the earthquakes which were detected in southern part of Japan during 2019. As for earthquakes with strike-slip mechanisms the P-waves could not be detected by our sensors. In addition, The conversion from seismic to acoustic waves can be happened through the generating of the T-phase from oceanic earthquakes. On 9 May 2019, progressive multi-channel cross correlation (PMCC) method applied infrasound and hydroacoustic waves from two earthquakes happened in west of Kyushu Island as the T-phase was well-recorded at H11N station near Wake Island. Moreover, infrasound propagation modeling is applied to the reconstructed atmosphere profile by Ground to Space Model (AVO-G2S) to confirm the infrasound arrivals, furthermore the 3D ray tracing process and the calculations by using the transmission loss equation with normal modes and parabolic equation methods are investigated. The study confirmed the infrasound generation scenario from the T-phase of oceanic propagation.

Study on Prediction Method of Infrasound Waves for Concrete Structure Destruction in Underground Space

To study the characteristics of infrasonic wave response during the failure process of concrete samples and analyze the feasibility of infrasonic wave prediction for the failure of concrete structures in underground spaces, rock mechanics loading devices and infrasonic wave acquisition devices were used to carry out infrasonic wave test experiments on concrete samples during uniaxial loading. With the help of MATLAB numerical simulation software, the test results are processed and analyzed by constructing band-pass filtering program, wavelet denoising program and time–frequency analysis program. The analysis results show that: there is infrasound wave during the loading process of the concrete sample; During the loading process, the change of infrasonic wave presents stage characteristics, which can be divided into three stages: the initial stage when a certain amount of infrasonic events occur, the middle stage when there are few infrasonic events and the later stage when infrasonic events increase rapidly and reach a peak. These stages respectively correspond to the compaction deformation stage, elastic deformation stage, plastic deformation and later stage of concrete sample deformation, and there is a good corresponding relationship between them. When the concrete sample is damaged by the peak value, the frequency and amplitude of the infrasound wave have abnormal changes. Therefore, in the early stage of the failure of the concrete structure, when the local failure occurs, there is also an abnormal response of infrasonic wave and the failure of the concrete structure can be predicted based on the abnormal change. At the same time, the infrasound wave, as a kind of low-frequency wave, has the advantages of long propagation distance, small attenuation and flexible position arrangement and has stronger adaptability to the complex underground space environment. It is of great significance to improve the accuracy of underground space concrete structure failure prediction.

Parameters of the Infrasonic Signal Generated in the Atmosphere by a Powerful Volcano Explosion

The purpose of this work is to represent the results of performing regression analysis to fit the distance and the amplitude of the infrasonic signal generated by the explosion of St. Helens volcano, and to estimate a few signal and atmospheric parameters. The pressure amplitude in the explosion wave generated at the beginning of St. Helens volcano eruption was measured at 13 stations in the 0.9 – 39-Mm distance range; based on these data, an attempt has been made to perform a regression analysis to fit amplitude and distance. The regression based on the assumption that the infrasound propagation takes place in a waveguide where it is subject to attenuation is determined to be the most preferable regression. Based on the observations of the shock from the St. Helens volcano eruption, the shock wave energy and mean power have been estimated to be ~1016 J and ~2.3 TW, respectively. Based on the observations of the amplitude and duration of the trains of the infrasonic wave generated by the St. Helens volcano eruption, the infrasonic wave energy and mean power have been estimated to be ~1016 J and ~2 TW, respectively. Both estimates are in good agreement, but they are significantly different from those found in the literature; the latter seem to be overestimated. From the regression expression obtained, the penetration depth of the infrasonic wave is obtained to be about 33 Mm, whereas at other stations this scale length is estimated to be close to 24 Mm. Based on the theoretical dependence of the attenuation coefficient due to atmospheric turbulence, the attenuation length of the infrasound wave has been estimated for infrasound with 10–300-s periods. For 20–300-s periods, this value has been shown to be significantly larger than the values determined from the observations. Other mechanisms for attenuating the infrasonic signal are discussed (the partial radiation of the infrasonic energy through and losses due to the reflection from the waveguide walls). At the same time, the wave attenuation due to their scattering by turbulent fluctuations can be significant for the periods smaller than 20–50 s, depending on the turbulence intensity. Comparison of the regression functions obtained with the corresponding regression expressions for other sources of infrasound waves propagating in the atmosphere has been made. Keywords: volcano eruption, infrasonic wave, shock wave, signal amplitude, regression, signal attenuation

Demultiplexing Infrasound Phonons With Tunable Magnetic Lattices

Controlling infrasound signals is crucial to many processes ranging from predicting atmospheric events and seismic activities to sensing nuclear detonations. These waves can be manipulated through phononic crystals and acoustic metamaterials. However, at such ultra-low frequencies, the size (usually on the order of meters) and the mass (usually on the order of many kilograms) of these materials can hinder its potential applications in the infrasonic domain. Here, we utilize tunable lattices of repelling magnets to guide and sort infrasound waves into different channels based on their frequencies. We construct our lattices by confining meta-atoms (free-floating macroscopic disks with embedded magnets) within a magnetic boundary. By changing the confining boundary, we control the meta-atoms’ spacing and therefore the intensity of their coupling potentials and wave propagation characteristics. As a demonstration of principle, we present the first experimental realization of an infrasound phonon demultiplexer (i.e., guiding ultra-low frequency waves into different channels based on their frequencies). The realized platform can be utilized to manipulate ultra-low frequency waves, within a relatively small volume, while utilizing negligible mass. In addition, the self-assembly nature of the meta-atoms can be key in creating re-programmable materials with exceptional nonlinear properties.

Atmospheric wind and temperature profiles inversion using infrasound: An ensemble model context.

This paper presents an inversion methodology where acoustic observations of infrasound waves are used to update an atmospheric model. This paper sought a flexible parameterization that permits to incorporate physical and numerical constraints without the need to reformulate the inversion. On the other hand, the optimization conveys an explicit search over the solution space, making the solver computationally expensive. Nevertheless, through a parallel implementation and the use of tight constraints, this study demonstrates that the methodology is computationally tractable. Constraints to the solution space are derived from the spread (variance) of ERA5 ensemble reanalysis members, which summarize the best current knowledge of the atmosphere from assimilated measurements and physical models. Similarly, the initial model temperature and winds for the inversion are chosen to be the average of these parameters in the ensemble members. The performance of the inversion is demonstrated with the application to infrasound observations from an explosion generated by the destruction of ammunition at Hukkakero, Finland. The acoustic signals are recorded at an array station located at 178 km range, which is within the classical shadow zone distance. The observed returns are assumed to come from stratospheric reflections. Thus, the reflection altitude is also an inverted parameter.