Infrasound Stations Research Articles

Evolving infrasound detections from Bogoslof volcano, Alaska: insights from atmospheric propagation modeling

Bogoslof volcano, a back-arc volcano in Alaska’s Aleutian arc, began an eruptive sequence in mid-December 2016 that ended in late August 2017, with 70 individual eruptive episodes. Because there were no local seismic or infrasound stations on the island, the Alaska Volcano Observatory (AVO) relied on distant geophysical networks and remote sensing techniques to assess activity during the eruption. AVO maintains six infrasound arrays to monitor activity along the Aleutian arc: Adak, the Island of Four Mountains, Okmok, Akutan, Sand Point, and Dillingham. Eruption detection at infrasound arrays is subject to local as well as mesoscale meteorological conditions that vary greatly over both short and long timescales. Infrasound detections from the array nearest to Bogoslof (Okmok), with a latency of about 3 min, played a crucial role in monitoring activity during the eruption. Despite the relative proximity of the Okmok array to Bogoslof (60 km), infrasound detections were not uniformly observed with only about two-thirds of the events successfully detected. The farthest array at Dillingham (816 km) detected approximately half of the explosive events, with all other arrays detecting less than half of the events. We compare observations with infrasound propagation model predictions, using both normal mode and parabolic equation forward models, to interpret the variation in detections of the 70 explosive events across the AVO infrasound network. The forward models utilize the newly created, publicly available AVO-G2S atmospheric reconstruction using numerical weather predictions data for the lower atmosphere, coupled with upper atmosphere empirical models of wind speeds and temperature. We find that long-range detections (> 100 km) of Bogoslof events are largely aligned with seasonal variability in favorable propagation conditions, while regional detections (< 100 km) are less consistent with propagation modeling. Understanding the output of numerical models in comparison to past observations will facilitate their use in future operational settings for AVO and other observatories.

A Comprehensive Study of Infrasound Signals Detected from the Ingolstadt, Germany, Explosion of 1 September 2018

The explosion at the Ingolstadt oil refinery was widely recorded at seismic and infrasound stations deployed throughout Central Europe, to distances of several hundred to a thousand kilometres. This study focuses on the wealth of data recorded at infrasound stations in Central and Eastern Europe, while from the many detecting seismic stations within 400 km range, only seismic and seismo-acoustic arrivals at the close-in Gräfenberg array are considered here. Most of the infrasound stations are acoustic arrays enabling us to apply array processing techniques to determine relevant wave field parameters, such as backazimuth and slowness (resp. trace velocity). These parameters not only confirm the source direction, but also put constraints on the observed arrivals’ propagation modes. Wave field parameters suggest that we observe tropospheric arrivals to about 150 km and stratospheric and/or thermospheric returns for longer distances. 1D, 2D and 3D ray tracing predict tropospheric arrivals to westerly directions up to distances of 100 km, beyond which only thermospheric returns are obtained azimuth-independent beyond 250–300 km. Stratospheric returns do not follow from any of the increasingly complex ray tracing models. Parabolic equation propagation modeling however suggests that in a number of cases stratospheric ducting may be possible. However, neither the tropospheric seismo-acoustic arrivals at the Gräfenberg array nor the various arrivals at IMS station IS26 could be modeled. Therefore, the Ingolstadt explosion along with the observed infrasonic phases provide an excellent test bed to investigate our ability in realistically forecasting atmospheric wave propagation with existing algorithms and available atmospheric models.

Global Monitoring and Characterization of Infrasound Signatures by Large Fireballs

Large meteoroids can be registered in infrasound recordings during their entry into the Earth’s atmosphere. A comprehensive study of 10 large fireball events of the years 2018 and 2019 highlights their detection and characterization using global infrasound arrays of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The study focuses on the observation and event analysis of the fireballs to estimate their respective location, yield, trajectory, and entry behavior. Signal characteristics are derived by applying the Progressive Multi-Channel Correlation method as an array technique. The comparison of the events with a NASA reference database as well as the application of atmospheric propagation modeling allows to draw conclusions about infrasound-based detection capability, localization accuracy, yield estimation, and source characterization. The infrasound technique provides a time- and location-independent remote monitoring opportunity of impacting near-Earth objects (NEOs), either independent or complementary to other fireball observation methods. Additionally, insights about the detection and localization capability of IMS infrasound stations can be gained from using large fireballs as reference events, being of importance for the continuous monitoring and verification of atmospheric explosions in a CTBT context.

Infrasound and seismoacoustic signatures of the 28 September 2018 Sulawesi super-shear earthquake

Abstract. A magnitude 7.5 earthquake occurred on 28 September 2018 at 10:02:43 UTC near the city of Palu on the Indonesian island of Sulawesi. It was a shallow, strike-slip earthquake with a rupture extending to a length of about 150 km and reaching the surface. Moreover, this earthquake was identified as one of very few events having a super-shear rupture speed. Clear and long-lasting infrasound signatures related to this event were observed by four infrasound arrays of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization as well as by one national infrasound station in Singapore. Although these infrasound stations SING (Singapore), I39PW (Palau), I07AU (Australia), I40PG (Papua New Guinea) and I30JP (Japan) are located at large distances of between 1800 and 4500 km from the earthquake's epicentral region, the observed infrasound signals associated with this event were intense, including both seismic and acoustic arrivals. A detailed study of the event-related infrasound observations and the potential infrasound generation mechanisms is presented, covering range-dependent infrasound transmission loss and propagation modeling and characterization of the atmospheric background conditions, as well as identification of the regions of seismoacoustic activity by applying a back-projection method from the infrasound receivers to potential source regions. This back projection of infrasonic arrivals allows one to estimate that the main infrasound source region for the Sulawesi earthquake is related to the extended rupture zone and the nearby topography. This estimation and a comparison to other super-shear as well as large regional earthquakes identify no clear connection between the earthquake's super-shear nature and the strong infrasound emission.

Combination of infrasound signals and complementary data for the analysis of bright fireballs

The flux densities of meteoroids and asteroids in the intermediate size range (approx. 20 cm – 30 m) impacting the Earth’s Atmosphere still have large uncertainties. There are too few objects of these sizes to be detected with localized fireball networks. Two detection methods that provide a global coverage of fireballs and bolides in this size range are infrasound monitors and space-based satellite sensors. Results from these sensors have large uncertainties specifically what concerns the energy release of the impacting bodies. In this paper a detailed analysis of infrasound data is performed to better understand recorded signals and uncertainties. This will allow to put the analysis and interpretation of infrasound data from impacts on a more solid scientific basis.Atmospheric impacts from large meteoroids or sometimes even asteroids generate infrasound signals which can often propagate over large distances and be registered at infrasound stations. The world-wide network of infrasound stations from the IMS (International Monitoring System) which is operated by the CTBTO (Comprehensive Nuclear-Test-Ban Treaty Organisation, Vienna, Austria) monitors most of the Earth’s Atmosphere and can detect the energy released by meteoroids. Hence, fireball infrasound signals can be used as a very promising information source for fireball research.Nonetheless, the data analysis is very complex and a topic of current discussions and research. In this paper a detailed analysis of the infrasound signals of some fireballs is carried out to be adapted to systematically calculate location, speed, and size or energy of the impacting objects from the infrasound data. Comparisons of other observation methods are also used for this purpose. Moreover, particular attention is paid to uncertainties in the analysis of infrasound data.The infrasound data analysis is part of the NEMO (NEar real-time MOnitoring system) project which started in autumn 2017. It is an information system analysing and combining data from multiple sources ranging from Social Media to infrasound data to monitor the impacts of fireballs on a global scale and to maximize the available scientific information.The infrasound data of the well-studied Chelyabinsk superbolide that exploded over southern Russia in 2013 and the Sulawesi, Indonesia, fireball that was registered in 2009 are reprocessed and the results compared to previous studies.To demonstrate the capacities and advantages of infrasound for the gathering of scientific information two recent fireballs are analysed in detail. These occurred on 08 March 2018 over Washington State (WS), USA, and on 21 June 2018 over the Ozerki region, Russia, respectively. For both fireballs infrasound signals were recorded making it possible to determine the source energy. We derived energies of about EWS=22tTNT and ERussia=2.4ktTNT using a published yield estimation relationship. Combining all available different data sources, which have information on these fireballs, ranging from rain radar to witness reports allowed us to derive a size (diameter) of the entering body in both cases, sWS=0.8m and. sRussia=3.8m.

How Can the International Monitoring System Infrasound Network Contribute to Gravity Wave Measurements?

Gravity waves (GWs) propagate horizontally and vertically in the atmosphere. They transport energy and momentum, and therefore GWs can affect the atmospheric circulation at different altitude layers when dissipating. Thus knowledge about the occurrence of GWs is essential for Numerical Weather Prediction (NWP). However, uniform networks for covering GW measurements globally are rare, especially in the troposphere. It has been shown that an infrasound station of the International Monitoring System (IMS) infrasound network is capable of measuring GWs at the Earth’s surface. The IMS was deployed for monitoring the atmosphere to verify compliance with the Comprehensive Nuclear-Test-Ban-Treaty. In this study, the Progressive Multi-Channel Correlation Method (PMCC) is used for re-processing up to 20 years of IMS infrasound recordings in order to derive GW detections. For this purpose, two alternative PMCC configurations are discussed, covering GW frequencies equivalent to periods of between 5 min and 150 min. These detections mainly reflect sources of deep convection, particularly in the tropics. At mid-latitudes, coherent wind noise more often produces spurious detections. Combining the results of both configurations provides a global dataset of ground-based GW measurements, which enables the calculation of GW parameters. These can be used for improving NWP models.

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.

Meteorological Source Variability in Atmospheric Gravity Wave Parameters Derived From a Tropical Infrasound Station

AbstractGravity waves are an important part of the momentum budget of the atmosphere. Despite this, parameterizations of gravity wave spectra in atmospheric models are poorly constrained. Gravity waves are formed by jet streams, flow over topography, and convection, all of which produce pressure perturbations as they propagate over the Earth's surface, detectable by microbarometer arrays used for sensing infrasound. In this study, observations of gravity waves between 2007 and 2011 at an infrasound station in the Ivory Coast, West Africa, are combined with meteorological data to calculate parameters such as intrinsic phase speed and wavenumber. Through spectral analysis, the seasonal and daily variations in all gravity wave parameters are examined. The gravity wave back azimuth varies with the migration of the Intertropical Convergence Zone, a region of intense convection, supporting previous studies. Daily variations in gravity wave arrivals at the station can be linked to two distinct convective cycles over the land and ocean. This was achieved by combining the gravity wave parameters with lightning strikes detected by the Met Office's Arrival Time Difference lightning detection system. Noise generated by turbulence in the middle of the day was found to attenuate smaller pressure amplitude gravity waves, artificially amplifying the daily variations in some gravity wave parameters. Detection of daily and seasonal variations in gravity wave parameters has the potential be used to improve the representation of gravity wave spectra in atmospheric models.

Porous domes as wind noise filters for infrasound sensing on Mars

The ability to detect infrasonic waves on Mars will enable further understanding of its environment. For example, infrasound arrivals from large storm systems, dust devils, and bolides can be used to understand source mechanisms and constrain impact statistics. The InSight microbarometer will measure the effect of ambient pressure fluctuations on seismometer data. It may also be able to detect infrasonic signals from distant sources, which, however, will be contaminated by wind noise. On Earth, infrasound stations use large-area spatial filters to reduce wind-noise contamination. These filters consist of long drilled pipes arranged radially around the sensor. Since this arrangement may not be easily deployable on Mars, we investigate the feasibility of tent-like porous domes, erected around the sensor, as wind-noise filters. Through theoretical modeling, we predict the power spectrum of wind pressure fluctuations at the center of the dome under Martian conditions. The results show that, as the porosity of the dome wall is lowered from 80% to 40%, a secondary wind-noise PSD peak is formed, moving from approximately 0.4 Hz–3 Hz, while the high-frequency “tail” (∼ 20 Hz) becomes stronger; low frequencies (f<0.1 Hz) show the typical characteristics of the energy-containing range. The porosity dependence shows promise in the potential to “adapt” the filter characteristics to various wind conditions. The research was supported by the Louisiana Space Grant Consortium (LaSPACE).

Generation of infrasonic signals during earthquakes under Lake Hovsgool (Northern Mongolia) on December 5, 2014

The paper discusses the results of the detection of seismic and infrasonic waves generated by a major earthquake and its aftershock (the moment magnitude MW=4.9 and MW=4.2 respectively), which occurred in northern Mongolia under Lake Hovsgool on December 5, 2014. The joint analysis of waveforms of seismic and infrasonic oscillations has shown that the signal recorded by the infrasound station of the Geophysical Observatory of the Institute of Solar-Terrestrial Physics SB RAS (ISTP SB RAS) is formed from sources of three generation types: local, secondary, and epicentral. This analysis enables us to propose a hypothesis of generation of epicentral infrasonic signal by flexural waves in an elastic ice membrane on the surface of Lake Hovsgool, which appear during the passage of seismic wave packets. This hypothesis explains the similarity between seismic and epicentral infrasonic signals, negative initial phase of epicentral infrasonic waves, and detection of a weak signal after a small-magnitude aftershock.

О генерации инфразвуковых сигналов при землетрясениях 5 декабря 2014 г. в акватории озера Хубсугул (северная Монголия)

The paper discusses the results of the detection of seismic and infrasonic waves generated by a major earthquake and its aftershock (the moment magnitude MW=4.9 and MW=4.2 respectively), which occurred in northern Mongolia under Lake Hovsgool on December 5, 2014. The joint analysis of waveforms of seismic and infrasonic oscillations has shown that the signal recorded by the infrasound station of the Geophysical Observatory of the Institute of Solar-Terrestrial Physics SB RAS (ISTP SB RAS) is formed from sources of three generation types: local, secondary, and epicentral. This analysis enables us to propose a hypothesis of generation of epicentral infrasonic signal by flexural waves in an elastic ice membrane on the surface of Lake Hovsgool, which appear during the passage of seismic wave packets. This hypothesis explains the similarity between seismic and epicentral infrasonic signals, negative initial phase of epicentral infrasonic waves, and detection of a weak signal after a small-magnitude aftershock.

Assessing middle atmosphere weather models using infrasound detections from microbaroms

SUMMARYThe nonlinear interaction of ocean surface waves produces coherent infrasound noise—microbaroms—between 0.1 and 0.5 Hz. Microbaroms propagate through the atmosphere over thousands of kilometres due to low absorption and efficient ducting between the ground and the stratopause. These signals are globally and permanently detected by the International Monitoring System (IMS) infrasound network, which has been established to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty. At the International Data Centre (IDC) in Vienna, where IMS data are routinely processed, microbarom detections appear in overlapping frequency bands, and are treated as false alarms. Therefore, understanding the variability in microbarom detections is essential to support the IDC in the reduction of the false alarm rate. In this study, microbarom amplitudes and the direction of arrivals at the German infrasound station IS26 were modelled. For the simulations, the source was described by an operational ocean wave interaction model, and the signal amplitude was modelled using a semi-empirical attenuation relation. This relation strongly depends on middle atmosphere (MA; i.e. 15–90 km altitude) dynamics; however, vertical temperature and wind profiles, provided by numerical weather prediction (NWP) models, exhibit significant biases and differences when compared with high-resolution light detection and ranging instrument (lidar) soundings in altitudes where infrasound signals propagate. To estimate uncertainties in the modelled amplitude, a fully autonomous lidar for MA temperature measurements was installed at IS26. Temperature and wind perturbations, considering observed biases and deviations, were added to the operational high-resolution atmospheric model analysis produced by the European Centre for Medium-Range Weather Forecasts. Such uncertainties in horizontal winds and temperature strongly impact propagation conditions, explaining almost 97 per cent of the actual detections, compared to 77 per cent when using the direct output of the NWP model only. Incorporating realistic wind and temperature uncertainties in NWP models can thus significantly improve the understanding of microbarom detections as well as the detection capability of a single station throughout the year.

Detection of Impact Points of Fragments of Spent Launch Vehicle Stages Using Infrasound Direction-Finding Methods

The paper describes the principles and techniques used to detect signals propagating in the atmosphere in the infrasonic frequency range. Such signals can be generated by different sources: ground and atmospheric explosions, as well as objects moving in the atmosphere at supersonic speed (aircraft, rockets, bolides, fragments of spent stages of launch vehicles). Portable infrasound monitoring stations are described, each of which includes three spaced infrasonic microphones. Each such station makes it possible to determine three basic parameters of the detected infrasound signal, which are subsequently used to solve the direction- finding problem: the time of arrival of an infrasonic wave, the azimuth to the source in the horizontal plane, and the wave approach angle from the source of infrasonic waves to the Earth’s surface in the vertical plane. An acoustic detector used to extract useful signals against a noise background is described. The detector is based on an algorithm similar to the STA/LTA detection algorithm known in seismology. Examples of the operation of an acoustic detector with data obtained during real measurements are given. Passive infrasound direction-finding technology is described. It is based on mathematical modeling of the of infrasonic wave propagation in the atmosphere, which are generated by objects moving along possible trajectories; comparison of theoretical signals with real ones recorded by monitoring stations; and determination of the realized trajectories. The paper gives examples of experimental verification of the effectiveness of passive infrasound direction-finding technology for determining the impact points of the first and second stages of launch vehicles. It is shown that infrasound direction-finding systems makes it possible to reduce the estimated search area for launch vehicle fragments that fall to the Earth, significantly decrease the time and costs for their search and utilization, and mitigate the negative environmental impact of the rocket and space industry.

The European Infrasound Bulletin

The European Infrasound Bulletin highlights infrasound activity produced mostly by anthropogenic sources, recorded all over Europe and collected in the course of the ARISE and ARISE2 projects (Atmospheric dynamics Research InfraStructure in Europe). Data includes high-frequency (> 0.7 Hz) infrasound detections at 24 European infrasound arrays from nine different national institutions complemented with infrasound stations of the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Data were acquired during 16 years of operation (from 2000 to 2015) and processed to identify and locate ∼ 48,000 infrasound events within Europe. The source locations of these events were derived by combining at least two corresponding station detections per event. Comparisons with ground-truth sources, e.g., Scandinavian mining activity, are provided as well as comparisons with the CTBT Late Event Bulletin (LEB). Relocation is performed using ray-tracing methods to estimate celerity and back-azimuth corrections for source location based on meteorological wind and temperature values for each event derived from European Centre for Medium-range Weather Forecast (ECMWF) data. This study focuses on the analysis of repeating, man-made infrasound events (e.g., mining blasts and supersonic flights) and on the seasonal, weekly and diurnal variation of the infrasonic activity of sources in Europe. Drawing comparisons to previous studies shows that improvements in terms of detection, association and location are made within this study due to increasing the station density and thus the number of events and determined source regions. This improves the capability of the infrasound station network in Europe to more comprehensively estimate the activity of anthropogenic infrasound sources in Europe.

Infrasound explosion and coda signal investigated with joint analysis of video at Mount Erebus, Antarctica

Mount Erebus is a natural laboratory where lava lake strombolian activity can be directly observed from the crater rim, allowing for a unique opportunity to study infrasound generated during explosive bubble bursting. Erebus lava lake eruptions occur when pressurized bubble slugs distend the lava lake surface and then burst within a few tenths of seconds. Data from two infrasound stations and one video camera were used to study 13 explosions occurring in January of 2006. Infrasound recordings from the two stations at ~330 m from the source exhibit variable amplitudes (40–160 Pa), but similar shapes composed of high-amplitude ~1 s bipolar pulses followed by codas exhibiting 3 or 4 decaying oscillations and lasting ~3 s. Infrasound pulses and infrasound-inferred source volumes are compared to video imagery, which is used to quantify the expanding volumes of distending bubbles and subsequent erupted pyroclasts. Video-inferred volumes scale well with infrasound-inferred volumes during the first few tenths of a second of an eruption, assuming a monopole source. Afterwards, an inflection in infrasound waveform, corresponding to a more rapid increase in the pressure record, indicates the fragmentation of the bubble membrane. At this point, infrasound is still produced by expanding gases and pyroclasts, but infrasound-inferred volumes are smaller than the image processing suggests. This is due to the fact that the image processing tracks ballistics, which expand inertially and without exerting a significant volume change. After 0.5 to 1.5 s the volumetric expansion is no longer evident in the infrasound record, which is now comprised of a coda characterized by decaying ~1 Hz oscillations. Because the coda does not correspond to any motions evident in the video, we conclude that it represents an acoustic resonance of the void left in the lava lake. This resonance is modulated by echoes off crater topography giving rise to two peak frequencies that dominate the coda spectra and are different for the two infrasound recording sites. The two coda spectral peaks are well explained by site-dependent propagation effects. Deconvolving crater topography effects, which are different for the two stations, reveals a single frequency peak at 1.5 Hz and is attributed to resonance of the void left in the lava lake, which we model as an open cylindrical pipe or Helmholtz resonance.

Local, Regional, and Remote Seismo‐acoustic Observations of the April 2015 VEI 4 Eruption of Calbuco Volcano, Chile

AbstractThe two major explosive phases of the 22–23 April 2015 eruption of Calbuco volcano, Chile, produced powerful seismicity and infrasound. The eruption was recorded on seismo‐acoustic stations out to 1,540 km and on five stations (IS02, IS08, IS09, IS27, and IS49) of the International Monitoring System (IMS) infrasound network at distances from 1,525 to 5,122 km. The remote IMS infrasound stations provide an accurate explosion chronology consistent with the regional and local seismo‐acoustic data and with previous studies of lightning and plume observations. We use the IMS network to detect and locate the eruption signals using a brute‐force, grid‐search, cross‐bearings approach. After incorporating azimuth deviation corrections from stratospheric crosswinds using 3‐D ray tracing, the estimated source location is 172 km from true. This case study highlights the significant capability of the IMS infrasound network to provide automated detection, characterization, and timing estimates of global explosive volcanic activity. Augmenting the IMS with regional seismo‐acoustic networks will dramatically enhance volcanic signal detection, reduce latency, and improve discrimination capability.

Parameters of Acoustic Signals Generated by the Atmospheric Meteoroid Explosion over Romania on January 7, 2015

System spectral analysis of temporal variations in the level of acoustic signals recorded at a number of European infrasound stations is carried out. The prevailing periods that varied within 3–5 s are found. Initial kinetic and acoustic energies of the Romanian meteoroid and infrasound parameters are calculated: celerity (280 m/s), acoustic efficiency, and stratospheric wind velocity (about 20 m/s). Parameters of cylindrical and explosive shock waves are found: duration, characteristic size, and amplitude. The dependence of the attenuation of infrasonic waves on distance is estimated. The results of the estimates are in good agreement with the results of the observations.

Parameters of the Infrasound Signal Generated by a Meteoroid over Indonesia on October 8, 2009

The basic parameters (delay time, celerity, duration, oscillation period, and amplitude) of the infrasound signal recorded by 17 stations are statistically analyzed as a function of the horizontal distance between the Indonesian superbolide total radiated energy and the infrasound station location. Fitting dependences of signal parameters on distance are given. Correlation diagrams are constructed and analyzed. The basic parameters of the meteoroid, the corrected value of the infrasound signal celerity, and the average tropospheric-stratospheric wind velocity are estimated.

Wind noise reduction at infrasound frequencies using large domes

One ongoing challenge to the use of infrasound for long-range monitoring applications (e.g., remote explosions or natural sources of infrasound such as tornados, volcanos or hurricanes) continues to be the high noise floors experienced at many permanent infrasound stations. International Monitoring System (IMS) infrasound stations typically address this problem using large pipe arrays as wind noise filters. However, these arrays generate significant distortion of higher frequency signals, making them non-ideal signals with significant frequency content above a few Hz. Further, they do not produce sufficient noise reduction during windy (typically daytime) measurements, making their utility generally limited to very quiet wind-noise periods (typically nighttime). Here we report on the development history of a 20-foot dome intended for permanent infrasound installations, and on measurements collected from arrays at the University of Mississippi Biological Field Station and at the Sandia National Laboratory Facility for Acceptance, Calibration, and Testing (FACT) site. The 20-foot dome at the FACT site is collocated with an IMS 18-m rosette filter and a University of Alaska Fairbanks experimental array, and more than a year of data has been collected, allowing for detailed comparisons of the efficacy of these different wind-noise reduction schemes.

A Study on the Correlation of Physiological and Psychological Health Hazards in Human Habitats with Seismicity, Mountain Air Turbulence and Environmental Infrasound

A statistical correlation study on the basis of published data has been performed in order to find whether an abnormal degree of human physiological ailments and a psychology of sustained violent reactions in highly populated habitats are correlated with environmental infrasound emissions related to seismic activity and sustained by mountain air turbulence. The study focus is on Latitude 34° North coinciding with boundaries of colliding Tectonic Plates in three continents. Earthquakes, rock fractures and landslides in these regions are creating geoacoustic activity in the form of hotspots of infrasound emissions. Sources of infrasound have been located by global infrasound monitoring stations. One single earthquake can cause multiple infrasound sources in a region. Low frequency “infrasound” creates an environment of unseen and inaudible energies that are hazardous to the local population. In one region on 34°N latitude the percentage of population with hearing disabilities increases or decreases almost directly proportional to frequency of earthquakes. In this region, the casualties due to social disorder and violence increased as the frequency of earthquake events increased and decreased as this frequency decreased. Comprehensive public health studies bring out that a sizable percentage of the regional population remain in a constant state of irritation, annoyance and anger; and suffer many other psychosomatic ailments corresponding to exposure to infrasound in 5 - 16 Hz frequencies and 120 - 140 dB amplitude. A new natural hazard inimical to life on planet earth has thus been identified. The time has arrived for public health authorities to locally pinpoint infrasound hotspots by scientific measurements. Thereafter new technologies can be developed to actively, and passively, mitigate/cancel these hazardous environmental emissions of infrasound and a Public Health Security Systems put in place as sustainable solutions for a healthy, livable habitat.