Infrasound Waves Research Articles

Design of a New Type of Optical Fiber Infrasound Sensor and Its Usage in Karst Geological Exploration

In this study, the demand of optical fiber (OF) sonic sensor is analyzed, and a composite OF infrasound sensor is proposed aiming at the detection demand of low-frequency infrasound waves in specific occasions. With this sensor, the polymer thin film and the aluminum soil can be combined to form a kind of composite film, the ECF/P interferometer can be formed between the end faces of the ferrule of the OF FC contact, the sensor head of the OF ECF/P infrasound sensor system is fabricated and then packaged. The designed OF infrasound sensor is used in the construction of a wireless sensor network (WSN) for karst geological exploration. The structure of the WSN includes the SimpliciTI communication network protocol, ADF7021 RF transceiver chip, STM32 processor chip, etc. New types of environment from karst can be sampled with this WSN. During the test, the performance of the composite OF infrasound sensor is analyzed at the beginning. The acoustic sensitivity of up to –136.73 dB re 1 V/μPa can be obtained in the low frequency infrasound range (1–20 Hz); the WSN based on the composite OF infrasound sensor has lower power consumption and faster networking speed. In addition, it can realize signal cover in karst areas without public mobile cellular networks, and send the information collected by the sensor to the data center, thus proving the fiber optic sound wave sensor designed in this study is successful and helpful for the geological prospectors to monitor the environment.

Utilizing the solution of sound diffraction by a thin screen to evaluate infrasound waves attenuated around volcano topography

The observation of infrasound signals in the vicinity of volcanoes is a powerful tool to understand the source of explosive volcanic activity. Although the propagation of infrasound signals is affected by the local topography, such effects are often ignored in the analysis, leading to potential misinterpretation of the source parameters. In this study, we propose a simple low-cost method of evaluating the attenuation of infrasound signals by topographical barriers. In this method, the first step approximates the elevation profile between the source and station into one thin screen-like barrier. Then, a mathematically exact solution of a sound diffraction problem is adopted to evaluate the attenuation of the infrasound amplitudes. To assess the validity of this method, the obtained estimates are compared with actual infrasound data observed at Sakurajima volcano, Japan. The results show that the estimates of relative amplitude to a reference station are more accurate than those considering only geometrical spreading, suggesting that the proposed method provides a useful first-order investigation of the attenuation of infrasound signals. The spatial distribution of the attenuation in the entire area of the volcano was also estimated, revealing a significant contrast between the eastern and western sides of the study area. Variations in signal attenuation also depend on the radial distance from the crater and were mainly attributed to variations of the relative screen height to the incident wavelength.

Assimilation of atmospheric infrasound data to constrain tropospheric and stratospheric winds

AbstractThis data assimilation study exploits infrasound from explosions to probe an atmospheric wind component from the ground up to stratospheric altitudes. Planned explosions of old ammunition in Finland generate transient infrasound waves that travel through the atmosphere. These waves are partially reflected back towards the ground from stratospheric levels, and are detected at a receiver station located in northern Norway at 178 km almost due north from the explosion site. The difference between the true horizontal direction towards the source and the backazimuth direction (the horizontal direction of arrival) of the incoming infrasound wavefronts, in combination with the pulse propagation time, are exploited to provide an estimate of the average cross‐wind component in the penetrated atmosphere. We perform offline assimilation experiments with an ensemble Kalman filter and these observations, using the ERA5 ensemble reanalysis atmospheric product as background (prior) for the wind at different vertical levels. We demonstrate that information from both sources can be combined to obtain analysis (posterior) estimates of cross‐winds at different vertical levels of the atmospheric slice between the explosion site and the recording station. The assimilation makes greatest impact at the 12–60 km levels, with some changes with respect to the prior of the order of 0.1–1.0 m·s−1, which is a magnitude larger than the typical standard deviation of the ERA5 background. The reduction of background variance in the higher levels often reached 2–5%. This is the first published study demonstrating techniques to implement assimilation of infrasound data into atmospheric models. It paves the way for further exploration in the use of infrasound observations – especially natural and continuous sources – to probe the middle atmospheric dynamics and to assimilate these data into atmospheric model products.

Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing.

Objective: We aim to examine the existing literature on, and identify knowledge gaps in, the study of adverse animal and human audiovestibular effects from exposure to acoustic or electromagnetic waves that are outside of conventional human hearing.Design/Setting/Participants: A review was performed, which included searches of relevant MeSH terms using PubMed, Embase, and Scopus. Primary outcomes included documented auditory and/or vestibular signs or symptoms in animals or humans exposed to infrasound, ultrasound, radiofrequency, and magnetic resonance imaging. The references of these articles were then reviewed in order to identify primary sources and literature not captured by electronic search databases.Results: Infrasound and ultrasound acoustic waves have been described in the literature to result in audiovestibular symptomology following exposure. Technology emitting infrasound such as wind turbines and rocket engines have produced isolated reports of vestibular symptoms, including dizziness and nausea and auditory complaints, such as tinnitus following exposure. Occupational exposure to both low frequency and high frequency ultrasound has resulted in reports of wide-ranging audiovestibular symptoms, with less robust evidence of symptomology following modern-day exposure via new technology such as remote controls, automated door openers, and wireless phone chargers. Radiofrequency exposure has been linked to both auditory and vestibular dysfunction in animal models, with additional historical evidence of human audiovestibular disturbance following unquantifiable exposure. While several theories, such as the cavitation theory, have been postulated as a cause for symptomology, there is extremely limited knowledge of the pathophysiology behind the adverse effects that particular exposure frequencies, intensities, and durations have on animals and humans. This has created a knowledge gap in which much of our understanding is derived from retrospective examination of patients who develop symptoms after postulated exposures.Conclusion and Relevance: Evidence for adverse human audiovestibular symptomology following exposure to acoustic waves and electromagnetic energy outside the spectrum of human hearing is largely rooted in case series or small cohort studies. Further research on the pathogenesis of audiovestibular dysfunction following acoustic exposure to these frequencies is critical to understand reported symptoms.

Ionospheric storm effects over the People’s Republic of China on 14 May 2019: Results from multipath multi-frequency oblique radio sounding

Results obtained from observations of ionospheric disturbances over the People’s Republic of China during the course of the geospace storm of 14 May 2019, one of the largest storms in 2019, are presented. The Harbin Engineering University operates the multi-frequency multipath radio wave diagnostics employing software defined technology and continuously monitoring dynamic process acting in the ionosphere at oblique incidence since April 2018. The basic premise upon which this instrument operation is based is that the digital re-sampling remains coherent with radio frequency for each propagation path, which permits Doppler spectra and signal amplitudes to be calculated along each of the 14 propagation paths. UT dependences of the Doppler spectra, the main mode Doppler shifts of frequency, and signal amplitudes that were measured on the day of the ionospheric storm and on the reference days of 13 and 15 May 2019 have been analyzed. After the magnetic storm onset, the Doppler shift of frequency exhibits an abrupt –1-Hz decrease, indicating the ionospheric storm onset. In addition, quasi-periodic variations in the Doppler shift of frequency, with 5-, 15-, 20-, and 30-min periods and the amplitudes in the range from 0.05 Hz to 0.15 Hz, occur in the course of the storm. These variations are due to modulation by infrasound (5-min period oscillation) and atmospheric gravity waves (15-, 20-, and 30-min period oscillations). In the electron density, the corresponding waves have amplitudes equal to 0.7% and 4–8%, respectively.

Infrasound and Gravity Waves Over the Andes Observed by a Pressure Sensor on Board a Stratospheric Balloon

AbstractThe study of infrasound (acoustic) and gravity waves sources and propagation in the atmosphere of a planet gives us precious insight on atmosphere dynamics, climate, and even internal structure. The implementation of modern pressure sensors with high rate sampling on stratospheric balloons is improving their study. We analyzed the data from the National Aeronautics and Space Administration Ultra Long Duration Balloon mission (16 May to 30 June 2016). Here, we focus on the balloon's transit of the Andes Mountains. We detected gravity waves that are associated to troposphere convective activity and mountain waves. An increase of the horizontal wavelengths from 50 to 70 km with increasing distance to the mountains is favoring the presence of mountain waves. We also report on the detection of infrasounds generated by the mountains in the 0.01–0.1 Hz range with a pressure amplitude increase by a factor 2 relative background signal. Besides, we characterized the decrease of microbaroms power when the balloon was flying away from the ocean coast. These observations suggest, in a way similar to microseisms for seismometers, that microbaroms are the main background noise sources recorded in the stratosphere even far from the ocean sources. Finally, we observed a broadband signal above the Andes, between 0.45 and 2 Hz, probably associated with a thunderstorm. The diversity of geophysical phenomena captured in less than a day of observation stresses the interest of high rate pressure sensors on board long‐duration balloon missions.

Infrasound Observations of Atmospheric Disturbances Due to a Sequence of Explosive Eruptions at Mt. Shinmoedake in Japan on March 2018

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.

Investigation of Infrasound Background Noise at Mátra Gravitational and Geophysical Laboratory (MGGL)

Infrasound and seismic waves are supposed to be the main contributors to the gravity-gradient noise (Newtonian noise) of the third-generation subterranean gravitational wave detectors. This noise will limit the sensitivity of the instrument at frequencies below 20 Hz. Investigation of its origin and the possible methods of mitigation have top priority during the designing period of the detectors. Therefore, long-term site characterizing measurements are needed at several subterranean sites. However, at some sites, mining activities can occur. These activities can cause sudden changes (transients) in the measured signal, and increase the continuous background noise, too. We have developed an algorithm based on discrete Haar transform to find these transients in the infrasound signal. We found that eliminating the transients decreases the variation of the noise spectra, and therefore results a more accurate characterization of the continuous background noise. We carried out experiments for controlling the continuous noise. Machines operating at the mine were turned on and off systematically in order to see their effect on the noise spectra. These experiments showed that the main contributor of the continuous noise is the ventilation system of the mine. We also estimated the contribution of infrasound Newtonian noise at MGGL to the strain noise of a subterranean GW detector similar to Einstein Telescope.

Investigation of infrasound signatures from microbaroms using OH airglow and ground-based microbarometers

In the frame of the European H2020 project ARISE, a short wave infrared (SWIR) InGaAs camera has been operated at the Haute-Provence Observatory, during a night that corresponds to the peak of Geminid meteor shower to investigate infrasound associated with meteor arrivals. This camera allows continuous observations during clear-sky nighttime of the OH airglow layer centered at 87 km. These observations were collocated with Rayleigh lidar measurements providing vertical temperature profiles from the lower stratosphere to the altitude of the OH layer around the mesopause. Spectral analysis of OH images did not allow to detect infrasound associated with meteor trails, however it reveals a peak corresponding to infrasound signals in the frequency band of those produced by ocean swell. Infrasound wave activity observed from ground-based microbarometers as well as the OH camera, appear to be modified with the presence of a temperature inversion described by Rayleigh lidar. Indeed, there is a difference in energy related to infrasonic activity between the first part of the night during the temperature inversion and after the inversion.

Relationship between the Parameters of Infrasound Waves and the Energy of the Source

Abstract—A new phenomenological model describing the propagation of acoustic disturbances in the stratospheric waveguide is proposed based on instrumental observations of infrasound signals from high-power explosive sources in the atmosphere. A generalized relationship between the energy of the acoustic source in the atmosphere and the characteristic frequency in the spectrum of the acoustic signal is obtained. The developed model is verified against the description of natural and manmade acoustic sources with the known energy. It is shown that the proposed model agrees with the observations and the data obtained in the other works.

Internal gravity and infrasound waves during a hurricane in Moscow On May 29, 2017

The results of recording of internal gravity waves (IGWs) and infrasound waves from the warm and cold fronts associated with the atmospheric storm passing through Moscow on May 29, 2017 are presented. The waves were recorded by a network of 4 microbarographs IFA–MGU–MSR–ZNS located in Moscow and Moscow region, and compared with the data of measurements of the parameters of infrasound waves at infrasound station IS43 in Dubna. We study the temporal changes in the characteristics of IGWs and infrasound waves (coherence, direction of propagation,phase velocities, characteristic periods and frequency spectra) with the passage of warm and cold fronts through the network. The transition from the gravity to the acoustic dispersive branch of acoustic-gravity waves due to an increase in frequency and the temporal modulation of the phase velocity of infrasound waves caused by IGWs are also studied. The measurement data for PM10 aerosol concentrations and NO2 gas concentrations at various locations in Moscow during a passage of atmospheric storm are presented. The possibility of detecting wave precursors of atmospheric storms simultaneously in variations of atmospheric pressure, wind velocity and aerosol concentrations is studied.

Internal Gravity and Infrasound Waves during the Hurricane of May 29, 2017, in Moscow

Data on internal gravity and infrasound waves recorded during the passage of both warm and cold fronts throughout Moscow, which are associated with the atmospheric storm of May 29, 2017, are given. These waves were recorded by four microbarographs located in the city of Moscow and Moscow region (and marked IFA, MGU, MSR, and ZNS in Fig. 1) and the data obtained were compared with data on infrasound waves recorded at the IS43 station in the town of Dubna. Time variations in the characteristics of internal gravity and infrasound waves (coherence, propagation azimuths, phase velocities, characteristic periods, and frequency spectra) during the passage of both warm and cold fronts are studied. The transition from the gravity to acoustic dispersive branch of acoustic-gravity waves due to increasing frequency and the temporal modulation of the phase velocity of infrasound waves due to internal gravity waves (IGWs) are also studied. Data on both aerosol (PM10) and gas (NO2) concentrations measured at different Moscow stations during the approaching atmospheric storm are given. The possibility of detecting wave precursors of atmospheric storms in simultaneous variations in atmospheric pressure, wind velocity, and pollutant concentrations is studied.

Monochromatic infrasound waves observed during the 2014\u20132015 eruption of Aso volcano, Japan

Monochromatic infrasound waves are scarcely reported volcanic infrasound signals. These waves have the potential to provide constraints on the conduit geometry of a volcano. However, to further investigate the waves scientifically, such as how the conduit shape modulates the waveforms, we still need to examine many more examples. In this paper, we provide the most detailed descriptions of these monochromatic infrasound waves observed at Aso volcano in Japan. At Aso volcano, a 160-day-long magmatic eruption occurred in 2014–2015 after a 20-year quiescent period. This eruption was the first event that we could monitor well using our infrasound network deployed around the crater. Throughout the entire eruption period, when both ash venting and Strombolian explosions occurred, monochromatic infrasound waves were observed nearly every day. Although the peak frequency of the signals (0.4–0.7 Hz) changed over time, the frequency exhibited no reasonable correlation with the eruption style. The source location of the signals estimated by considering topographic effects and atmospheric conditions was highly stable at the active vent. Based on the findings, we speculate that these signals were related to the resonant frequencies of an open space in the conduit: the uppermost part inside the vent. Based on finite-difference time-domain modeling using 3-D topographic data of the crater during the eruption (March 2015), we calculated the propagation of infrasound waves from the conduit. Assuming that the shape of the conduit was a simple pipe, the peak frequency of the observed waveforms was well reproduced by the calculation. The length of the pipe markedly defined the peak frequency. By replicating the observed waveform, we concluded that the gas exhalation with a gas velocity of 18 m/s occurred at 120 m depth in the conduit. However, further analysis from a different perspective, such as an analysis of the time difference between the arrivals of infrasound and seismic waves, is required to more accurately determine the conduit parameters based on observational data.

Analytical modelling and characterisation of an infrasound generator in the air

This paper presents an accurate characterisation based on an experimental set-up and mathematical models of a dynamic pressure infrasound generator. The Commissariat à l’énergie atomique (CEA) has developed microbarometers to measure infrasound waves in the atmosphere. To characterise its sensors and validate their requirements, an infrasound generator has been designed, which covers a frequency range from 4.0 10−4 Hz to 300 Hz. This pressure generator still needs accurate characterisation as there is no standard reference in the infrasound frequency range for such sensor calibration. The research focused on 17 parameters that affect the behaviour of this infrasound pressure generator. Two analytical models of the sound pressure in the cylindrical cavity of the calibrator are presented. An experimental characterisation was also performed to adjust the model parameters with genetic algorithms to the measurements, and the results of the comparison between the measurements and the models are discussed. This study highlights the influence of the thermodynamic transition from isothermal to adiabatic transformation and the influence of viscoelastic non-linearities of a loudspeaker membrane. It aims to characterise the amplitude and phase responses of the generator in order to develop an improved infrasound calibration device for microbarometers with a similar technology.

Generation of Infrasound Waves at Sites of Underground Mine Collapses

AbstractIn 2015 and 2016, collapse‐induced earthquakes, accompanied by surface subsidence, occurred at two underground mines in South Korea and were followed by impulsive infrasound signals that were detectable at distances greater than 200 km. To explain the infrasound generation caused by the collapses, we hypothesize that excess pressure was released by the rapid outflow of an underground air mass into the atmosphere caused by the sudden implosion of earth into the underground space. We tested this idea with a physical model that assumes a displaced air volume as a monopole source with reduced pressure. The estimated volumes of the two collapses were ~1.7 × 105 and ~7.3 × 105 m3, respectively, which agrees with the collapse volumes inferred from surface subsidence data. The infrasound generation model we used is applicable to the monitoring of other catastrophic failures within manmade or natural subsurface cavities.

Using infrasound waves to monitor tropospheric weather and crater morphology changes at Volcán Tungurahua, Ecuador

We use infrasound waves generated during eruptions of Volcán Tungurahua (Ecuador) to study both, changing atmospheric conditions and volcanic source characteristics. Analyzed infrasound data were recorded for a 32-month period by a five-station network located within 6.5km from the vent. We use cross-network correlation to quantify the recurrent eruptive behavior of Tungurahua and results are corroborated by reports from the Ecuadorian monitoring agency. Cross-network lag times vary over short time periods (minutes to days) when vent location is stable and attribute these variations to changes in atmospheric structure. Assuming a fixed source location, we invert for average air temperatures and winds in Tungurahua's vicinity (<6.5km) and find evidence for diurnal and semidiurnal tropospheric tides. We also use cross-network correlation lag times to compute infrasound source positions with resolutions of ~11.6m, taking into account coarse NOAA atmospheric models for local winds and temperatures. Variable infrasound-derived source locations suggest source migration during the 32months of analyzed data. Such source position variability is expected following energetic eruptions that destructively altered the crater/vent morphology as confirmed by imagery obtained during regular overflights.

Time–space variations in infrasound sources related to environmental dynamics around Lützow–Holm Bay, east Antarctica

Characteristic features of infrasound waves observed in the Antarctic reflect the physical interaction between the surface environment along the continental margin and the surrounding Southern Ocean. The temporal–spatial variability of the source locations for infrasound excitation during the eight-month period between January and August 2015 was investigated using recordings made by two infrasound arrays deployed along a section of the coast of Lützow–Holm Bay (LHB), Antarctica. The infrasound arrays clearly detected temporal variations in frequency content and propagation direction during this period. A number of infrasound sources were identified, many located north of the arrays. Many of the events had a predominant frequency content of a few Hz, higher than microbaroms from the ocean. A comparison of the results with MODIS satellite images indicated that these infrasound sources were ice-quakes associated with the calving of glaciers, the breaking off of sea ice, and collisions between this sea ice and icebergs around the LHB. Continuous measurements of infrasound in the Antarctic may serve as a proxy for monitoring the regional surface environment in terms of climate change at high southern latitudes.

Infrasound in the ionosphere from earthquakes and typhoons

Infrasound waves are observed in the ionosphere relatively rarely, in contrast to atmospheric gravity waves. Infrasound waves excited by two distinguished sources as seismic waves from strong earthquakes (M > 7) and severe tropospheric weather systems (typhoons) are discussed and analyzed. Examples of observation by an international network of continuous Doppler sounders are presented. It is documented that the co-seismic infrasound is generated by vertical movement of the ground surface caused by seismic waves propagating at supersonic speeds. The coseismic infrasound propagates nearly vertically and has usually periods of several tens of seconds far away from the epicenter. However, in the vicinity of the epicenter (up to distance about 1000–1500 km), the large amplitudes might lead to nonlinear formation of N-shaped pulse in the upper atmosphere with much longer dominant period, e.g. around 2 min. The experimental observation is in good agreement with numerical modeling. The spectral content can also be nonlinearly changed at intermediate distances (around 3000–4000 km), though the N-shaped pulse is not obvious. Infrasound waves associated with seven typhoons that passed over Taiwan in 2014–2016 were investigated. The infrasound waves were observed at heights approximately from 200 to 300 km. Their spectra differed during the individual events and event from event and covered roughly the spectral range 3.5–20 mHz. The peak of spectral density was usually around 5 mHz. The observed spectra exhibited fine structures that likely resulted from modal resonances. The infrasound was recorded during several hours for strong events, especially for two typhoons in September 2016.

Characteristic atmosphere and ocean interaction in the coastal and marine environment inferred from infrasound at Terra Nova Bay, Antarctica - observation and initial data -

Characteristic features of infrasound waves observed in the Antarctic reveal physical interaction involving surface environments around the continent and Southern Ocean. In December 2015, an infrasound array (100 m spacing) by three sensors (Chaparral Physics Model 25, with a detectable frequency range of 0.1-200 Hz), together with a broadband barometer (Digiquartz Nano-Resolution Model 6000-16B Barometer, with a detectable frequency range of 0-22 Hz) were installed at Jang Bogo Staion, Terra Nova Bay, Antarctica by the Korea Arctic and Antarctic Research Program (KAARP). The initial data recorded by the broadband barometer contain characteristic signals originated by surrounding environment, including local noises such as katabatic winds. Clear oceanic signals (microbaroms) are continuously recorded as the background noises with predominant frequency around 0.2 s at the austral summer on December. Variations in their frequency context and amplitude strength in Power Spectral Density had been affected by an evolution of sea-ice surrounding the Terra Nova Bay. Microbaroms measurement is a useful tool for characterizing ocean wave climate, complementing other oceanographic, cryospheric and geophysical data in the Antarctic. Continuous infrasound observations in Terra Nova Bay attain a new proxy for monitoring environmental changes such as the global warming, involving cryosphere dynamics, as well as the volcanic eruptions in Northern Victoria Land, Antarctica.

Infrasound and internal gravity waves generated by atmospheric storms

The recordings of infrasound and internal gravity waves (IGWs) obtained during 2015-2016 at infrasound station I43 IMS and a network of microbarographs installed by Obukhov Institute of Atmospheric Physics (OIAP) are presented. The OIAP network of microbarographs is capable of detecting simultaneously an infrasound at frequencies less than 3 Hz and IGWs with periods ranging from 5 min to 3 hr. It is shown that the low-frequency wave processes generated by atmospheric fronts retain high coherence (0.6-0.9) over the areas with horizontal dimensions of a few tens of km. It is found that after the passage of atmospheric front the internal wave trains were observed with the amplitudes considerably exceeding those of IGWs that were detected before the passage of the atmospheric front. The discrete periods of 35 min, 56 min, and 110 min were found in the frequency spectra of the observed wave trains. For these periods, the coherence between atmospheric pressure variations measured at different points reach local maxima, and the sum of the phase differences between selected three points tends to zero. The phase speeds for the observed IGWs are in the range of 10-50 m/c. The wave “precursors” with amplitudes of 10 Pa and periods of 15-20 min were also detected 10 to 15 hr before a passage of the atmospheric front through a network. Along with IGWs, the infrasound associated with atmospheric front was also detected (August 2016) by I43 in the frequency range 0.1-0.4 Hz.