Infrasound Measurements Research Articles

Nonlinear Moment-Tensor Inversion of Repetitive Long-Periods Events Recorded at Pacaya Volcano, Guatemala

Detailed models of low-frequency seismicity at volcanoes provide insights into conduit structure and dynamics of magmatic systems. We examine explosion-related long-period (LP) events from Pacaya volcano, Guatemala, that were recorded during a temporary installation of four broadband seismic stations from October 2013 to November 2013. The repetitive LP events are identified with the aid of infrasound measurements using a matched filter due to the high level of background tremor and the small magnitude of the recorded events. We derive a representative seismic signal from the phase-weighted stack of 8,587 of these similar events, and invert for a source moment tensor. To address the limitations posed by the limited number of stations of the local network, we employ a non-linear waveform inversion that uses a grid search for source type to obtain a quantitative measure of the source mechanism reliability. With only four stations, Pacaya represents a case of limited observational data, where a quantitative description of moment tensor uncertainty is needed before any interpretation is to be attempted. Results point to a shallow source mechanism somewhat like a tension crack, dipping ~ 40° to the east, consistent with the dominant E-W motion in the seismic records from stations west, north, and east of the source. The uncertainties determined from the non-linear inversion are not insignificant, but clearly constrain the mechanism to be a source dominated by isotropic components

Wind turbine low frequency and infrasound propagation and sound pressure level calculations at dwellings.

This study was developed to estimate wind turbine low frequency and infrasound levels at 1238 dwellings in Health Canada's Community Noise and Health Study. In field measurements, spectral peaks were identifiable for distances up to 10 km away from wind turbines at frequencies from 0.5 to 70 Hz. These measurements, combined with onsite meteorology, were in agreement with calculations using Parabolic Equation (PE) and Fast Field Program (FFP). Since onsite meteorology was not available for the Health Canada study, PE and FFP calculations used Harmonoise weather classes and field measurements of wind turbine infrasound to estimate yearly averaged sound pressure levels. For comparison, infrasound propagation was also estimated using ISO 9613-2 (1996) calculations for 63 Hz. In the Health Canada study, to a distance of 4.5 km, long term average FFP calculations were highly correlated with the ISO based calculations. This suggests that ISO 9613-2 (1996) could be an effective screening method. Both measurements and FFP calculations showed that beyond 1 km, ISO based calculations could underestimate sound pressure levels. FFP calculations would be recommended for large distances, when there are large numbers of wind turbines, or when investigating specific meteorological classes.

Modeling of the mechanism of appearance of external infrasound of land vehicles

The main contribution to the acoustic pollution of residential areas is made by land vehicles including automobiles. Most scientific publications are devoted to the study of audible sound, its sources in the vehicle and the development of measures to reduce it. According to the authors opinion, at present the problem of the emergence and spread of infrasound in residential areas, and, accordingly, its negative impact on people and the environment is underestimated. Hence the development of computational and experimental methods for studying the mechanism of the appearance of infrasound from a vehicle is a very urgent problem. A large proportion of the acoustic radiation from the vehicle falls on infrasound and low-frequency range of frequencies. Depending on the design of the automobile, the occurrence of internal infrasound can be caused by the engine's vibrations as a rigid body on its suspension, flexural and torsional body oscillations, the impact of the oncoming airflow. Measurements of internal and external infrasound were carried out. A computational model is proposed and an assessment is made of the influence of the design features of the vehicle on the level of infrasound. Calculation studies of the mechanism of the appearance of an external infrasound of a vehicle have shown that its frequency and level depend on the speed of movement, the drag coefficient, the length and the Strouhal number. A significant source of infrasound in the automobile are also wheels that perform rotational and translational movements in the oncoming air stream. Calculation of five wheel harmonics for a automobile at various speeds of movement is carried out, existing dependences are revealed. The results of the calculation showed that exceeding the normative values of infrasound is possible only in residential areas adjacent to the traffic flow with speeds of over 80 km / h.

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.

Possibility of the use of data of infrasonic monitoring for identification of the nature of seismic events

The paper considers the possibility of the use of infrasound measurements conducted in Ukraine to verify the recorded seismic events and the use of infrasound data as one of the criteria for their identification. Registration of seismic and infrasonic signals was carried out via a network of geophysical Main center of special monitoring. To register infrasound small-aperture infrasound arrays were used, allowing directional monitoring of events. The data of 909 parameters of seismic events from industrial explosions that occurred during 2014 in Ukraine have been obtained. 124 infrasonic responses on these events have been registered. The limits of sensitivity and distance of the use of infrasound method have been found. The proposed technology of registering signals from seismic events by seismic-acoustic complex makes possible to register surface industrial explosions at a distance of 200 kilometers.

Infrasound and low frequency sound emitted from tornados

The NCPA, in collaboration Hyperion Technology Group, has performed a series of measurements of infrasound and low-frequency sound generated by tornadic thunderstorms near Oklahoma City, OK, during a large-scale outbreak on May 24, 2011. Ground truth for tornado tracks as well as meteorological data were available for these storms. Infrasound and low-frequency sound were identified separately for a long duration EF-5, an EF-4, and an EF-2 tornado. As reported by Frazier et al. [JASA 135, 1742 (2014)], infrasound in two distinct regions were noted: An infrasound band between approximately 1-10 Hz and a low-frequency audible band located between roughly 40-200 Hz (center frequency around 80-100 Hz). As part of the NOAA VORTEX-SE initiative, the NCPA will be collecting additional infrasound data in the Northern portion of Alabama, centered on Huntsville and the Sand Mountain region. Current plans are to install to 10 infrasound arrays, with seven elements per array. As part of the same VORTEX-SE initiative, seven additional arrays will be deployed by the University of Alabama Huntsville. We will report here on the status of infrasound generated by tornadic thunderstorms, as well as discuss the status of modeling efforts to understand the origins of these emissions.

Refinement of bolide characteristics from infrasound measurements

We have detected and performed signal measurements on 78 individual bolide events as recorded at 179 infrasound stations between 2006 and 2015. We compared period-yield relations with AFTAC nuclear period-yield data, finding these to be similar with a slight offset. Scatter in period measurements for individual bolide is found to be caused in part by station noise levels and by attenuation effects with range. No correlation was found between the infrasound signal period and any of bolide height at peak brightness, entry speed or impact angle. We examined in detail three well constrained bolides having energy deposition curves, known trajectories and infrasound detections finding some evidence at shorter ranges that a component of station period scatter is due to varying source heights sampled by different stations. However, for longer-range stations in these three case studies, we were not able to assign unique source heights using raytracing due to large uncertainties in atmospheric conditions. Our results suggest that while source height contributes to the observed variance in infrasound signal periods from a given bolide, range and station noise play a larger role.

Comparison and Validation of Acoustic Response Models for Wind Noise Reduction Pipe Arrays

AbstractThe detection capability of the infrasound component of the International Monitoring System (IMS) is tightly linked to the performance of its wind noise reduction systems. The wind noise reduction solution implemented at all IMS infrasound measurement systems consists of a spatial distribution of air inlets connected to the infrasound sensor through a network of pipes. This system, usually referred to as “pipe array,” has proven its efficiency in operational conditions. The objective of this paper is to present the results of the comparison and validation of three distinct acoustic response models for pipe arrays. The characteristics of the models and the results obtained for a defined set of pipe array configurations are described. A field experiment using a newly developed infrasound generator, dedicated to the validation of these models, is then presented. The comparison between the modeled and empirical acoustic responses shows that two of the three models can be confidently used to estimate pipe array acoustic responses. This study paves the way to the deconvolution of IMS infrasound data from pipe array responses and to the optimization of pipe array design to IMS applications.

The Study on Vibroacoustic Characteristics of Shunting Locomotive Cabin

Power plant of shunting locomotive is a powerful source of infrasound. If the level of infrasound is more than 100dB, the time of operator work should be limited. The paper presents a simultaneous measurement of infrasound and low-frequency vibration at various modes and loads. The levels of infrasound and low-frequency vibration were measured inside the cabin and near the shunting locomotive. It was detected that infrasound depends on low-frequency vibration. There was a relationship between the level of infrasound and the opened window inside the cabin. Some recommendations to reduce the infrasound level were developed. The results indicate, overall, that the level of infrasound exceeds the standard values. The implementation of developed recommendation could reduce the level of infrasound.

Long-Term Variations in Infrasound Signals Observed at Syowa Station, Antarctica: 2008-2014

Long-term Infrasound data at Syowa Station (SYO; 39E, 69S), in the Lützow-Holm Bay (LHB), East Antarctica was analyzed during the period from 2008 to 2014. Seasonal variations in microbaroms and high-frequency harmonic tremors were especially investigated. Infrasound data were strongly involved in local dynamics of surface environments. The microbaroms have relatively low amplitudes in austral winters by extending area of sea-ice around LHB, with decreasing oceanic swell loading effects. The other reasons of seasonal variations in microbaroms amplitudes were caused by the affections of a number of storms during whole year and snow accumulation over the porous hoses on the infrasound station at SYO. In contrast, non-linear high-frequency harmonic tremors were considered to be caused by the katabatic winds from Antarctic continent flowing in northeast dominant orientation. The high-frequency tremors had characteristics of daily variations in particular in austral summer. It is required to continue more than a few years of observation in order to identify relationships with climate change and global warming effects in the Antarctic. Continuous measurement of infrasound in the coastal margin of Antarctica is a proxy for monitoring multi-sphere interaction between the continent and surrounding Southern Ocean.

Exploring the signature of polar lows in infrasound: the 19–20 November 2008 cases

We report in this study the infrasound signal measured consistently at four stations in Fennoscandia, associated with the development of two intense cyclones, called polar lows, over the Norwegian Sea. When conditions of propagation are favourable, the infrasound signal comes from the direction of the polar lows, and it follows their track. The results thus, tend to confirm those of a previous study who claimed that an outbreak of three polar lows generated clear infrasound to distances up to 1000 km, according to measurements acquired in Northern Norway and on Svalbard. Because the conditions of propagation of infrasound depend on the state of the atmosphere between the sources and the receivers, signals may remain undetected, which limits the capability of a systematic early warning system, and also of a global monitoring of polar lows. However, the recorded signals might reflect on-going source processes, since convection associated with the polar lows is detected using microwave satellite observations in the areas from which the signals emanate. This suggests that at least part of the signal is due to turbulence induced by convection, in agreement with the earlier study. Nevertheless, more evidence of broadband infrasound measurements of polar low cases have to be examined in order to be able to fully assess the role of other possible sources (swell, surf, lightnings, …). The addition in Northern Norway in late 2013 of the IS37 infrasound station of the International Monitoring Network, developed for the verification of the Comprehensive nuclear-Test-ban Treaty, will provide new opportunities to further investigate this issue.

Field Measurements of Terrestrial and Martian Dust Devils

Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimensions, but only limited constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of dust abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of diagnostic dust devil signals within seismic and infrasound measurements; an upcoming Mars robotic mission will obtain similar measurement types.

Using infrasound to constrain ash plume rise

Airborne volcanic ash advisories are currently based on analyses of satellite imagery with relatively low temporal resolution, and numerical simulations of atmospheric plume dispersion. These simulations rely on key input parameters such as the maximum height of eruption plumes and the mass eruption rate at the vent, which remain loosely constrained. In this study, we present a proof-of-concept workflow that incorporates the analysis of volcanic infrasound with numerical modelling of volcanic plume rise in a realistic atmosphere. We analyse acoustic infrasound records from two explosions during the 2009 eruption of Mt. Redoubt, USA, that produced plumes reaching heights of 12–14 km. We model the infrasonic radiation at the source under the assumptions of linear acoustic theory and calculate variations in mass ejection velocity at the vent. The estimated eruption velocities serve as the input for numerical models of plume rise. The encouraging results highlight the potential for infrasound measurements to be incorporated into numerical modelling of ash dispersion, and confirm their value for volcano monitoring operations.

Infrasound as a Detector of Local and Remote Turbulence

Infrasound measurements are used to detect seismic waves and a large effort is devoted to eliminating the turbulence-related infrasound signal, usually considered as noise. Here we take a complementary approach, investigating whether infrasound can provide information on atmospheric turbulence. Microphone measurements of infrasound from an experimental campaign in Hungary in 2013 are used, together with data from a nearby sonic anemometer and a sodar. The comparison of infrasound integrated spectral energy to turbulent kinetic energy from the sonic provides a good match when turbulence is present near the ground. Moreover, on stable nights when the surface layer is strongly stratified and with turbulence absent, microphones sometimes recorded infrasound when the sodar showed a low-level jet above the surface inversion, indicating that microphones may be used as detectors of elevated turbulence.

Seismic and infrasonic analysis of the 9 March 2014 fireball in South Korea

On the evening of 9 March 2014, a bright fireball was observed in many places in South Korea, the energy associated with the event was also recorded at local seismic and regional infrasound stations. Using impulsive seismic signals recorded at 19 stations, we calculated the possible extent of the sonic source of the fireball by assuming point- and line-source models, which might be physically linked to either a point-source explosion in the atmosphere or shock waves radiating from the fireball’s trail, respectively. By comparing the observed seismic arrival times with those predicted by both models, a line-source model resulted in better solution than a point-source model. It means that shock waves along the meteor’s high-speed passage through the atmosphere probably acted as the dominant source of the seismic signals. The parameters of the fireball’s sonic trajectory, after incorporating a realistic sound velocity model of the atmosphere, are estimated to be an azimuth arrival angle of 313.5° clockwise from the north and an elevation arrival angle of 44.5° above the Earth’s surface, with a time of 11:04:51 UTC at which the trajectory meets the Earth’s surface. The estimated ground impact point is about 2 km offset from locations where meteorites associated with the fireball were found. The line-source model also explained the large azimuthal deviation of infrasound waves observed at arrays in the vicinity of the trajectory. From the infrasound measurements, the kinetic local-source energy generating the sound was estimated to be approximately 0.8 tons TNT, based on semi-empirical relations for the point- and line-source models.

The validation of SSWs forecasts in atmospheric global circulation models

While the influence of the troposphere on the stratosphere is well known, recent observational and modeling studies have demonstrated that the stratosphere has an impact on the troposphere as well. The dynamical coupling between stratosphere and troposphere is particularly strong during sudden stratospheric warming (SSW) events. The correct forecasting of the onset and duration of SSW events is therefore important and is a current challenge for weather forecasting centers. As there is a lack of observations in the upper stratosphere with good temporal and spatial coverage, additional techniques may be helpful to constrain SSWs. This is illustrated using volcanic infrasound measurements. The observations are compared with nowcast and forecast models up to 10 days. While a general agreement is found during the summer period, larger discrepancies are found during the equinox and major SSW of January 2013.

Дослiдження взаємозв'язкiв функцii кровообiгу людини та рiвня iнфразвукового фону в умовах Антарктики

The highest values of the average level of infrasound in the Antarctic region in the range of 6 -7 Hz were observed from July to September, and the lowest in March. There are, however, short periods of exceedances of the threshold of sensitivity, even in the relatively quiet time. With an average level of 60 dB background waves above the threshold of 90 dB. In such conditions for winterers at the station (especially in case of adaptation), this may lead to deterioration in performance and psychological state. In this regard, the study of the reaction of the organism winterers оn the effects of infrasound is very important. The aim of this work is the study of the nature of the influence of infrasound vibrations to the function of the circulatory system in the Antarctic winterers. Given these results, simultaneous monitoring for the year of  hibernation, during which from April to October, daily, twice а day, measured blооd pressure (ВР) and heart rate (НR) at each of the winterers (n= 11). Meteorological parameters of the atmospheric pressure was measured with five-minute intervals were averaged to two values оn the day. The same procedure was subjected to the value of infrasound measurements (initial increments of 20 Hz). Cluster analysis based оn the values of heart rate, systolic and diastolic blооd pressure allowed to divide the totality of healthy winterers in two groups  which  are represented  bу features of the circulation tо determine whether effects оn winterers infrasound was conducted multi-regression analysis, whereby it is established that for а cluster, "0" , the correlation coefficient exceeds а value of 0.51. This result indicates а significant influence оn blооd pressure of atmospheric pressure and background levels of infrasound. It is shown that the zero group of the cluster in general is very sensitive to meteorological factors, manifestation of which is including infrasound (for example, bу lowering the atmospheric pressure is often increased wind speed in the surface layer, and the wind is powerful infrasound generator). Almost always there is some dependence: if the level of infrasound increases the coherence of a series of physiological data. In addition, in the time interval (from 1 April to 1 October) there has been а steady growth rate of the coherence of the entire cohort winterers, that may bе associated with alterations of adaptive mechanisms, development desynchronizing manifestations under changed photoperiodic, or other causes. Ву visual comparison of the graphs of physiological coherency series graphs of the dynamics of the level of infrasound, we саn distinguish the following pattern: when the level of infrasound there is а slight increase in the level of coherence of the physiological data, which confirms the existence of а relationship between physiological parameters and external factors

Measurement and synthesis of wind turbine infrasound

As part of an ongoing investigation into the putative subjective effects of sub-20 Hz acoustical emissions from large industrial wind turbines, measurement techniques for faithful capture of emissions waveforms have been developed and reported. To evaluate perception thresholds, Fourier synthesis and high fidelity low-frequency playback equipment has been used to duplicate in a residential-like listening environment the amplitudes and wave slopes of the actual emissions, with pulsation rate in the range of 0.5–1.0 per second. Further, the amplitudes and slopes of the synthesized waves can be parametrically varied and the harmonic phases “scrambled” to assess the relative effects on auditory and other subjective responses. Measurement and synthesis system details and initial subjective response results will be shown.

Tropical deep convection and density current signature in surface pressure: comparison between WRF model simulations and infrasound measurements

Abstract. Deep convection is a major atmospheric transport process in the tropics, affecting the global weather and the climate system. In the framework of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project, we combine model simulations of tropical deep convection with in situ ground measurements from an IMS (International Monitoring System) infrasound station in the Ivory Coast to analyze the effects of density current propagation. The WRF (Weather Research and Forecasting) model is firstly run in a simplified (referred to as "idealized case") and highly resolved configuration to explicitly account for convective dynamics. Then, a coarser three-dimensional simulation (referred to as "real") is nudged towards meteorological reanalysis data in order to compare the real case with the idealized model and in situ observations. In the 2-D run, the evolution of a deep convective cloud generates a density current that moves outward up to 30 km away from storm center. The increase in surface density (up to 18 g m−3 larger than surrounding air) is mostly due to the sudden temperature decrease (down to −2 °C, with respect to the domain-averaged value) from diabatic cooling by rain evaporation near ground level. It is accompanied by a dramatic decrease in relative humidity (down to −50%), buoyancy (down to −0.08 m s−2), equivalent potential temperature (25 °C lower than the planetary boundary layer (PBL)) and the rapid enhancement of horizontal wind speed (up to 15 m s−2). If temperature and density changes are strong enough, surface pressure becomes largely affected and high-frequency disturbances (up to several tens of Pa) can be detected at the leading edges of density current. The moister and warmer air of subcloud layer is lifted up and replaced by a more stable flow. The resulting thermodynamical instabilities are shown to play a key role in triggering new convection. If the initial environment is sufficiently unstable, they can give rise to continuous updrafts that may lead to the transition from single-cell to multicell cloud systems, even without the presence of an initial wind shear. The overall consistence and similarity between idealized and real simulation, and the good agreement of the real case with in situ retrievals of temperature, pressure, wind speed and direction, seem to confirm the ability of 2-D and 3-D models to well reproduce convective dynamics. Surface pressure disturbances, simulated in both the idealized and real cases as a consequence of cold pool propagation, are very similar to those recorded in the Ivory Coast. Present results stress the direct link between mesoscale convective system activity and high-frequency surface pressure variations, suggesting the possibility of developing a new method for real-time rainstorm tracking based on the ground-based infrasound monitoring of pressure field.

Characterization and interpretation of volcanic activity at Karymsky Volcano, Kamchatka, Russia, using observations of infrasound, volcanic emissions, and thermal imagery

A multiparameter data set including measurements of infrasound, volcanic emissions, and thermal imagery is used to characterize and interpret diverse volcanic activity observed during field campaigns in August 2011 and July 2012 at Karymsky Volcano, Kamchatka, Russia. Four activity types are visually identified and characterized according to: SO2 emission rate, ash mass, event duration, peak temperature, thermal radiation energy, infrasound onset and frequency, reduced infrasonic pressure, and acoustic energy. These activity types include: (1) ash explosions, (2) pulsatory degassing, (3) gas jetting, and (4) explosive eruption. Unique infrasound signals are associated with all four activity types suggesting that infrasound can be used to help remotely and continuously detect and characterize volcanic activity at Karymsky and other similar volcanoes. Our observations suggest that SO2 is emitted continuously, though in varying abundance, while ash is emitted discontinuously and is only associated with certain types of activity. Our data set supports previous models that attribute variations in surface activity to changes in conduit permeability at Karymsky Volcano. Evidence for a decrease in conduit permeability as a trigger for ash explosions and explosive eruption activity types is supported by weakened but still detectable SO2 emission rates prior to eruption, along with the highly impulsive infrasonic onset and large reduced infrasound pressure indicating high pressure at the vent. We speculate that changes in conduit permeability at Karymsky Volcano result from changes in magma supply from the shallow‐crustal storage region though additional measurements are required to validate this hypothesis.