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Milton Garces - One of the best experts on this subject based on the ideXlab platform.
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an analysis of ground shaking and transmission loss from infrasound generated by the 2011 tohoku earthquake
Journal of Geophysical Research, 2013Co-Authors: Ilyoung Che, Kristoffer T Walker, C D De Groothedlin, Alexis Le Pichon, Tae Sung Kim, Milton GarcesAbstract:[1] The 2011 Mw9.0 Tohoku earthquake generated infrasound that was recorded by nine infrasonic arrays. Most arrays recorded a back azimuth variation with time due to the expanse of the source region. We use ray tracing to predict group velocities and back azimuth wind corrections. A Japan accelerometer network recorded ground shaking in unprecedented spatial resolution. We back projected infrasound from arrays IS44 (Kamchatka) and IS30 (Tokyo) to the source region and compare these results with acceleration data. IS44 illuminates the complex geometry of land areas that experienced shaking. IS30 illuminates two volcanoes and a flat area around the city of Sendai, where the maximum accelerations occurred. The arrays and epicentral region define three source-receiver profiles. The observed broadband energy transmission loss (TL) follows an exponential decay law. The best fitting model, which has parameters that are interpreted to include the effects of geometric spreading, scattering, and the maximum ratio of the effective sound speed in the stratosphere to that at the ground (accounts for stratospheric wind speed), yields a 65% variance reduction relative to predictions from a traditional TL relationship. This model is a simplified version of the model of Le Pichon et al. (2012), which yields an 83% variance reduction for a single frequency, implying that fine-scale atmospheric structure is required to explain the TL for stratospheric upwind propagation. Our results show that infrasonic arrays are sensitive to ground acceleration in the source region of megathrust earthquakes. The TL results may improve infrasonic amplitude scaling laws for explosive yield.
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on infrasound standards part 1 time frequency and energy scaling
InfraMatics, 2013Co-Authors: Milton GarcesAbstract:A standardized, self-similar, multiresolution algorithm is developed for scaling infrasonic signal time, frequency, and power within the framework of fractional octave bands. This work extends accepted fractional octave band schemas to 0.001 Hz (1000 s periods) to facilitate the analysis of broadband signals as well as the deep acoustic-gravity and Lamb waves captured by the global infrasound network. The Infrasonic Energy, Nth Octave (INFERNO) multiresolutionEnergy Estimator is applied to computing the total acoustic energy of the Russian meteor signature recorded in the 45mHz-9 Hz frequency band by IMS array 131KZ, Kazakhstan.
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infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007
Journal of Geophysical Research, 2010Co-Authors: Robin S Matoza, David Fee, Milton GarcesAbstract:[1] Long-lived effusive volcanism at the Pu`u `Ō`ō crater complex, Kilauea Volcano, Hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years. Previous studies showed that this infrasonic tremor wavefield can be recorded at a range of >10 km. However, the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range. In April 2007, we supplemented a broadband infrasound array at ∼12.5 km from Pu`u `Ō`ō (MENE) with a similar array at ∼2.4 km from the source (KIPU). The additional closer-range data enable further evaluation of tropospheric propagation effects and provide higher signal-to-noise ratios for studying volcanic source processes. The infrasonic tremor source appears to consist of at least two separate physical processes. We suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor. Low-frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma-air interface. We further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low-velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle. The infrasonic tremor arrives with a median azimuth of ∼67° at KIPU. Additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex (median azimuth ∼77°) coincided with turbulent degassing activity at a new lava tube skylight. Our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at Kilauea Volcano.
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The rotary subwoofer : A controllable infrasound source
Journal of the Acoustical Society of America, 2009Co-Authors: Joseph Park, Milton Garces, Bruce ThigpenAbstract:The rotary subwoofer is a novel acoustic transducer capable of projecting infrasonic signals at high sound pressure levels. The projector produces higher acoustic particle velocities than conventional transducers which translate into higher radiated sound pressure levels. This paper characterizes measured performance of a rotary subwoofer and presents a model to predict sound pressure levels.
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the source of infrasound associated with long period events at mount st helens
Journal of Geophysical Research, 2009Co-Authors: Robin S Matoza, Milton Garces, Michael A H Hedlin, C D De Groothedlin, Bernard Chouet, Luca Dauria, G P WaiteAbstract:[1] During the early stages of the 2004–2008 Mount St. Helens eruption, the source process that produced a sustained sequence of repetitive long-period (LP) seismic events also produced impulsive broadband infrasonic signals in the atmosphere. To assess whether the signals could be generated simply by seismic-acoustic coupling from the shallow LP events, we perform finite difference simulation of the seismo-acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere. The effects of topography, velocity structure, wind, and source configuration are considered. The simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of P/SV and Rayleigh wave energy converted locally along the propagation path, and acoustic energy originating from the source epicenter. Although the horizontal acoustic velocity of the latter is consistent with our data, the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations, and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source. The observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic LP events. The observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated, highly permeable material. Heating by magmatic activity causes pressure to rise, periodically reaching the pressure threshold for rupture of the “valve” sealing the crack. Sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack, initiating resonance of the remaining fluid. Subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13.4 km to the NW of the volcano are attributed primarily to atmospheric boundary layer propagation effects, superimposed upon amplitude changes at the source.
Robin S Matoza - One of the best experts on this subject based on the ideXlab platform.
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infrasonic crackle and supersonic jet noise from the eruption of nabro volcano eritrea
Geophysical Research Letters, 2013Co-Authors: David Fee, Tracianne B Neilsen, Robin S Matoza, Kent L. Gee, Darcy E OgdenAbstract:The lowermost portion of an explosive volcanic eruption column is considered a momentum-driven jet. Understanding volcanic jets is critical for determining eruption column dynamics and mitigating volcanic hazards; however, volcanic jets are inherently difficult to observe due to their violence and opacity. Infrasound from the 2011 eruption of Nabro Volcano, Eritrea has waveform features highly similar to the crackle phenomenon uniquely produced by man-made supersonic jet engines and rockets and is characterized by repeated asymmetric compressions followed by weaker, gradual rarefactions. This infrasonic crackle indicates that infrasound source mechanisms in sustained volcanic eruptions are strikingly similar to jet noise sources from heated, supersonic jet engines and rockets, suggesting that volcanologists can utilize the modeling and physical understandings of man-made jets to understand volcanic jets. The unique, distinctive infrasonic crackle from Nabro highlights the use of infrasound to remotely detect and characterize hazardous eruptions and its potential to determine volcanic jet parameters. Key Points Nabro Volcano produced sound similar to supersonic jet engines and rockets Volcanic and man-made jets have similar sound source mechanisms Infrasound can remotely detect and characterize volcanic eruptions and jets. © 2013. American Geophysical Union. All Rights Reserved.
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infrasound data inversion for atmospheric sounding
Geophysical Journal International, 2012Co-Authors: Jerome Lalande, Olivier Sebe, Matthieu Landes, Ph Blancbenon, Robin S Matoza, Le A Pichon, E BlancAbstract:SUMMARY The International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) continuously records acoustic waves in the 0.01–10 Hz frequency band, known as infrasound. These waves propagate through the layered structure of the atmosphere. Coherent infrasonic waves are produced by a variety of anthropogenic and natural sources and their propagation is controlled by spatiotemporal variations of temperature and wind velocity. Natural stratification of atmospheric properties (e.g. temperature, density and winds) forms waveguides, allowing long-range propagation of infrasound waves. However, atmospheric specifications used in infrasound propagation modelling suffer from lack and sparsity of available data above an altitude of 50 km. As infrasound can propagate in the upper atmosphere up to 120 km, we assume that infrasonic data could be used for sounding the atmosphere, analogous to the use of seismic data to infer solid Earth structure and the use of hydroacoustic data to infer oceanic structure. We therefore develop an inversion scheme for vertical atmospheric wind profiles in the framework of an iterative linear inversion. The forward problem is treated in the high-frequency approximation using a Hamiltonian formulation and complete first-order ray perturbation theory is developed to construct the Frechet derivatives matrix. We introduce a specific parametrization for the unknown model parameters based on Principal Component Analysis. Finally, our algorithm is tested on synthetic data cases spanning different seasonal periods and network configurations. The results show that our approach is suitable for infrasound atmospheric sounding on a regional scale.
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infrasonic observations of the june 2009 sarychev peak eruption kuril islands implications for infrasonic monitoring of remote explosive volcanism
Journal of Volcanology and Geothermal Research, 2011Co-Authors: Robin S Matoza, Ilyoung Che, Alexis Le Pichon, Julien Vergoz, Pascal Herry, J Lalande, Heeil Lee, Alexander V RybinAbstract:Abstract Sarychev Peak (SP), located on Ostrov Matua, Kurils, erupted explosively during 11–16 June 2009. Whereas remote seismic stations did not record the eruption, we report atmospheric infrasound (acoustic wave ~ 0.01–20 Hz) observations of the eruption at seven infrasound arrays located at ranges of ~ 640–6400 km from SP. The infrasound arrays consist of stations of the International Monitoring System global infrasound network and additional stations operated by the Korea Institute of Geoscience and Mineral Resources. Signals at the three closest recording stations IS44 (643 km, Petropavlovsk-Kamchatskiy, Kamchatka Krai, Russia), IS45 (1690 km, Ussuriysk, Russia), and IS30 (1774 km, Isumi, Japan) represent a detailed record of the explosion chronology that correlates well with an eruption chronology based on satellite data (TERRA, NOAA, MTSAT). The eruption chronology inferred from infrasound data has a higher temporal resolution than that obtained with satellite data. Atmosphere-corrected infrasonic source locations determined from backazimuth cross-bearings of first-arrivals have a mean centroid ~ 15 km from the true location of SP. Scatter in source locations of up to ~ 100 km result from currently unresolved details of atmospheric propagation and source complexity. We observe systematic time-variations in trace-velocity, backazimuth deviation, and signal frequency content at IS44. Preliminary investigation of atmospheric propagation from SP to IS44 indicates that these variations can be attributed to solar tide variability in the thermosphere. It is well known that additional information about active volcanic processes can be learned by deploying infrasonic sensors with seismometers at erupting volcanoes. This study further highlights the significant potential of infrasound arrays for monitoring volcanic regions such as the Kurils that have only sparse seismic network coverage.
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infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007
Journal of Geophysical Research, 2010Co-Authors: Robin S Matoza, David Fee, Milton GarcesAbstract:[1] Long-lived effusive volcanism at the Pu`u `Ō`ō crater complex, Kilauea Volcano, Hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years. Previous studies showed that this infrasonic tremor wavefield can be recorded at a range of >10 km. However, the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range. In April 2007, we supplemented a broadband infrasound array at ∼12.5 km from Pu`u `Ō`ō (MENE) with a similar array at ∼2.4 km from the source (KIPU). The additional closer-range data enable further evaluation of tropospheric propagation effects and provide higher signal-to-noise ratios for studying volcanic source processes. The infrasonic tremor source appears to consist of at least two separate physical processes. We suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor. Low-frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma-air interface. We further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low-velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle. The infrasonic tremor arrives with a median azimuth of ∼67° at KIPU. Additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex (median azimuth ∼77°) coincided with turbulent degassing activity at a new lava tube skylight. Our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at Kilauea Volcano.
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the source of infrasound associated with long period events at mount st helens
Journal of Geophysical Research, 2009Co-Authors: Robin S Matoza, Milton Garces, Michael A H Hedlin, C D De Groothedlin, Bernard Chouet, Luca Dauria, G P WaiteAbstract:[1] During the early stages of the 2004–2008 Mount St. Helens eruption, the source process that produced a sustained sequence of repetitive long-period (LP) seismic events also produced impulsive broadband infrasonic signals in the atmosphere. To assess whether the signals could be generated simply by seismic-acoustic coupling from the shallow LP events, we perform finite difference simulation of the seismo-acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere. The effects of topography, velocity structure, wind, and source configuration are considered. The simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of P/SV and Rayleigh wave energy converted locally along the propagation path, and acoustic energy originating from the source epicenter. Although the horizontal acoustic velocity of the latter is consistent with our data, the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations, and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source. The observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic LP events. The observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated, highly permeable material. Heating by magmatic activity causes pressure to rise, periodically reaching the pressure threshold for rupture of the “valve” sealing the crack. Sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack, initiating resonance of the remaining fluid. Subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13.4 km to the NW of the volcano are attributed primarily to atmospheric boundary layer propagation effects, superimposed upon amplitude changes at the source.
Michael A H Hedlin - One of the best experts on this subject based on the ideXlab platform.
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infrasound connecting the solid earth oceans and atmosphere
Annual Review of Earth and Planetary Sciences, 2012Co-Authors: Michael A H Hedlin, Kristoffer T Walker, D P Drob, C D De GroothedlinAbstract:The recently reinvigorated field of Infrasonics is poised to provide insight into atmospheric structure and the physics of large atmospheric phenomena, just as seismology has shed considerable light on the workings and structure of Earth’s solid interior. Although a natural tool to monitor the atmosphere and shallow Earth for nuclear explosions, it is becoming increasingly apparent that infrasound also provides another means to monitor a suite of natural hazards. The frequent observation of geophysical sources—such as the unsteady sea surface, volcanoes, and earthquakes—that radiate energy both up into the atmosphere and down into the liquid or solid Earth and transmission of energy across Earth’s boundaries reminds us that Earth is an interconnected system. This review details the rich history of the unheard sound in the atmosphere and the role that Infrasonics plays in helping us understand the Earth system.
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the source of infrasound associated with long period events at mount st helens
Journal of Geophysical Research, 2009Co-Authors: Robin S Matoza, Milton Garces, Michael A H Hedlin, C D De Groothedlin, Bernard Chouet, Luca Dauria, G P WaiteAbstract:[1] During the early stages of the 2004–2008 Mount St. Helens eruption, the source process that produced a sustained sequence of repetitive long-period (LP) seismic events also produced impulsive broadband infrasonic signals in the atmosphere. To assess whether the signals could be generated simply by seismic-acoustic coupling from the shallow LP events, we perform finite difference simulation of the seismo-acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere. The effects of topography, velocity structure, wind, and source configuration are considered. The simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of P/SV and Rayleigh wave energy converted locally along the propagation path, and acoustic energy originating from the source epicenter. Although the horizontal acoustic velocity of the latter is consistent with our data, the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations, and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source. The observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic LP events. The observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated, highly permeable material. Heating by magmatic activity causes pressure to rise, periodically reaching the pressure threshold for rupture of the “valve” sealing the crack. Sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack, initiating resonance of the remaining fluid. Subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13.4 km to the NW of the volcano are attributed primarily to atmospheric boundary layer propagation effects, superimposed upon amplitude changes at the source.
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infrasonic jet noise from volcanic eruptions
Geophysical Research Letters, 2009Co-Authors: Robin S Matoza, David Fee, Milton Garces, J M Seiner, Patricio Ramon, Michael A H HedlinAbstract:[1] The lowermost section of a Vulcanian or Plinian volcanic eruption column may be thought of as a momentum-driven, turbulent, free-shear jet flow. We propose that large-amplitude and long-duration infrasonic (<20 Hz) signals recorded at ranges of tens of kilometers during powerful eruptions at Mount St. Helens, USA, and Tungurahua, Ecuador, represent a low frequency form of jet noise. A preliminary test of this hypothesis is made by comparing the observed infrasonic spectra to the empirically-derived similarity spectra for pure-air jets. Although the spectral shapes are in approximate agreement, the observed volcanic signals have additional complexities not present in the pure-air laboratory data. These features may result from multiphase flow containing solid particles and liquid droplets, very high temperatures, and perhaps complex crater morphology. However, the overall similarity between the volcanic signals and jet noise indicates that broadband infrasound measurements at volcanoes may provide a quantitative link to eruption jet dynamics, and would aid substantially in the remote assessment of volcanic hazard.
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seismic and acoustic recordings of an unusually large rockfall at mount st helens washington
Geophysical Research Letters, 2008Co-Authors: Seth C Moran, Robin S Matoza, Milton Garces, Michael A H Hedlin, D Bowers, William E Scott, David R Sherrod, James W VallanceAbstract:[1] On 29 May 2006 a large rockfall off the Mount St. Helens lava dome produced an atmospheric plume that was reported by airplane pilots to have risen to 6,000 m above sea level and interpreted to be a result of an explosive event. However, subsequent field reconnaissance found no evidence of a ballistic field, indicating that there was no explosive component. The rockfall produced complex seismic and infrasonic signals, with the latter recorded at sites 0.6 and 13.4 km from the source. An unusual, very long-period (50 s) infrasonic signal was recorded, a signal we model as the result of air displacement. Two high-frequency infrasonic signals are inferred to result from the initial contact of a rock slab with the ground and from interaction of displaced air with a depression at the base of the active lava dome.
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an infrasound array study of mount st helens
Journal of Volcanology and Geothermal Research, 2007Co-Authors: Robin S Matoza, Michael A H Hedlin, Milton GarcesAbstract:The ongoing activity of Mount St. Helens provides an opportunity to study the infrasonic wavefield produced by an active, silica-rich volcano. In late October 2004, as a pilot experiment for the Acoustic Surveillance for Hazardous Eruptions (ASHE) project, we deployed two infrasound arrays, each co-located with a broadband seismometer and weather station, to continuously record seismo-acoustic signals from Mount St. Helens. The nearest array, Coldwater, was deployed on the northern flank of the volcano, ∼ 13 km from the summit. The second array, Sacajawea, was deployed ∼ 250 km east of the volcano, at a distance where stratospherically ducted acoustic waves may be expected during the winter. This paper presents an overview of the experimental setup, and preliminary results from this unique data set. Eruptions on January 16th 2005 and March 9th 2005 produced strong infrasonic signals. The aseismic January 16th eruption signal lasted ∼ 9.4 min beginning at ∼ 11:20:44 01/16/05 UTC, while the March 9th eruption signal lasted ∼ 52.8 min beginning at ∼ 01:26:17 03/09/05 UTC, with the main steam and ash venting stage probably lasting ∼ 7.2 min. The March 9th signal was an order of magnitude larger than the January 16th signal, and was clearly recorded 250 km east at the Sacajawea array. Infrasonic expressions of long period (LP) seismic events (‘drumbeats’) have also been intermittently observed, and are recorded as acoustic waves mimicking the waveform and temporal sequence of their seismic counterparts. These acoustic observations provide important constraints for source models of long period events and eruptions.
L G Evers - One of the best experts on this subject based on the ideXlab platform.
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Performance Assessment of Geophysical Instrumentation Through the Automated Analysis of Power Spectral Density Estimates
'American Geophysical Union (AGU)', 2021Co-Authors: M. R. Koymans, Domingo J. Ballesta, E. Ruigrok, R. Sleeman, L. Trani, L G EversAbstract:Abstract This study describes an automated data quality verification procedure supported by a database of power spectral densities (PSD) estimates for geophysical waveform data. The Royal Netherlands Meteorological Institute (KNMI) manages a 100‐TB archive of continuous geophysical data collected from accelerometers, geophones, broadband seismometers, and infrasonic arrays deployed across the continental and Caribbean Netherlands. This rapidly expanding network at a scale of over 700 instruments makes the manual evaluation of data quality impractical and must be supported by data policies and automated methods. A technique is presented to compress and store PSD estimates in a database with a storage footprint of less than 0.05% of the raw data archive. Every week, the instrument performance is validated by comparing statistical properties of its latest monthly probabilistic PSD distribution to strict quality metrics. The criteria include thresholds based on global noise models, datalogger quantization noise models, constraints imposed by ambient noise conditions, and confidence intervals based on PSD estimates calculated from validated archived data. When a threshold is crossed, the station operator is alerted of the suspected degraded instrument performance, severely limiting the required amount of manual labor and associated human errors. The automated PSD assessment technique is applicable to accelerometers, geophones, broadband seismometers, infrasonic stations, and is demonstrated to be extendable to hydrophones, gravimeters, tiltmeters, and Global Navigation Satellite System receivers. The approach is therefore suitable for other geophysical monitoring infrastructures, for example, observational networks dedicated to continuous volcano monitoring. It is shown that it possible to detect degraded instrument performance that may otherwise remain undetected
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bidirectional infrasonic ducts associated with sudden stratospheric warming events
Journal of Geophysical Research, 2014Co-Authors: Jelle Assink, Pieter Smets, L G Evers, Roger WaxlerAbstract:In January 2011, the state of the polar vortex in the midlatitudes changed significantly due to a minor sudden stratospheric warming event. As a result, a bidirectional duct for infrasound propagation developed in the middle atmosphere that persisted for 2 weeks. The ducts were due to two zonal wind jets, one between 30 and 50 km and the other around 70 km altitude. In this paper, using microbarom source modeling, a previously unidentified source region in the eastern Mediterranean is identified, besides the more well known microbarom source regions in the Atlantic Ocean. Infrasound data are then presented in which the above mentioned bidirectional duct is observed in microbarom signals recorded at the International Monitoring System station I48TN in Tunisia, from the Mediterranean region to the east and from the Atlantic Ocean to the west. While the frequency bands of the two sources overlap, the Mediterranean signal is coherent up to about 0.6 Hz. This observation is consistent with the microbarom source modeling; the discrepancy in the frequency band is related to differences in the ocean wave spectra for the two basins considered. This work demonstrates the sensitivity of infrasound to stratospheric dynamics and illustrates that the classic paradigm of a unidirectional stratospheric duct for infrasound propagation can be broken during a sudden stratospheric warming event.
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infrasonic signature of the 2009 major sudden stratospheric warming
Geophysical Research Letters, 2009Co-Authors: L G Evers, P SiegmundAbstract:The study of infrasound is experiencing a renaissance since it was chosen as a verification technique for the Comprehensive Nuclear-Test-Ban Treaty. The success of the verification technique strongly depends on knowledge of upper atmospheric processes. The ability of infrasound to probe the upper atmosphere starts to be exploited, taking the field beyond its monitoring application. Processes in the stratosphere couple to the troposphere and influence our daily weather and climate. Infrasound delivers actual observations on the state of the stratosphere with a high spatial and temporal resolution. Here we show the infrasonic signature, passively obtained, of a drastic change in the stratosphere due to the major sudden stratospheric warming (SSW) of January 2009. With this study, we infer the enormous capacity of infrasound in acoustic remote sensing of stratospheric processes on a global scale with surface based instruments.
Liang Liu - One of the best experts on this subject based on the ideXlab platform.
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observation of fundamental thermal noise in optical fibers down to infrasonic frequencies
Applied Physics Letters, 2016Co-Authors: Jing Dong, Junchao Huang, Liang LiuAbstract:The intrinsic thermal noise in optical fibers represents the ultimate limit for fiber-based systems. However, at infrasonic frequencies, the spectral behavior of the intrinsic thermal noise is still unclear. In this letter, we present measurements of the fundamental thermal noise in optical fibers that are obtained using a balanced fiber Michelson interferometer. When an ultra-stable laser is used as the laser source and other noise sources are carefully controlled, the 1/f spectral density of the thermal noise is observed down to infrasonic frequencies, and the measured magnitude is consistent with the results of theoretical predictions at frequencies over the range from 0.2 Hz to 20 kHz. Moreover, as observed experimentally, the level of the 1/f thermal noise can be reduced by changing the coatings of the optical fibers. This therefore indicates one possible way to reduce thermal noise in optical fibers at low Fourier frequencies. Finally, the inconsistency between the experimental data and the existing...
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Observation of Fundamental Thermal Noise in Optical Fibers down to Infrasonic Frequencies
Applied Physics Letters, 2016Co-Authors: Jing Dong, Junchao Huang, Liang LiuAbstract:The intrinsic thermal noise in optical fibers is the ultimate limit of fiber-based systems. However, at infrasonic frequencies, the spectral behavior of the intrinsic thermal noise remains unclear so far. We present the measurements of the fundamental thermal noise in optical fibers obtained using a balanced fiber Michelson interferometer. When an ultra-stable laser is used as the laser source and other noise sources are carefully controlled, the 1/f spectral density of thermal noise is observed down to infrasonic frequencies and the measured magnitude is consistent with the theoretical predictions at the frequencies from 0.2 Hz to 20 kHz. Moreover, as observed in the experiment, the level of 1/f thermal noise is reduced by changing the coating of optical fibers. Therefore, a possible way to reduce the thermal noise in optical fibers at low Fourier frequencies is indicated. Finally, the inconsistency between the experimental data on thermomechanical noise and existing theory is discussed.