Evaluating the applicability of a screen diffraction approximation to local volcano infrasound

Maher, Sean; Matoza, Robin S.; Groot‐Hedlin, Catherine de; Kim, Kee Hoon; Gee, Kent L.

doi:10.30909/vol.04.01.6785

Cited by 15 publications

(14 citation statements)

References 70 publications

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“…The observations made across Ascension Island (Sec. 5) show that understanding both 2D barrier and 3D diffraction effects are important when interpreting near-horizontal infrasound propagation across complex terrain (in agreement with Maher et al, 2021). Although a significant proportion of the topographic influence on acoustic propagation across Ascension Island can be explained by 2D barrier effects, diffraction around hill H 2 between the source and L 2 leads 2D simulations to underpredict sound levels in the lee of the hill.…”

Section: Discussionsupporting

confidence: 61%

Three-dimensional topographic effects on infrasound propagation across Ascension Island

Khodr

Green

Azarpeyvand

2022

Geophysical Journal International

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Summary Narrowband harmonic infrasound signals within the 1 to 8 Hz passband, generated by wind turbines on Ascension Island, have been recorded at four microbarometers located at distances of between 1.8 and 4.6 km from the source along different azimuths. Across one month of recordings in October 2010, amplitude ratios between the four recordings show temporal stability but deviate from the ratios expected for propagation across a flat plane. Using a recently developed three-dimensional parabolic equation method, that can incorporate realistic topography as a lower boundary, it is shown that these time-independent amplitude ratio deviations can be, in part, explained by acoustic interactions with topography that has scale lengths on the order of a few hundreds of metres. These interactions comprise both two-dimensional barrier effects that reduce sound levels behind high topography, and three-dimensional diffractive effects that increase sound levels behind topographic obstacles. For the Ascension Island case study, amplitudes along two of the four paths can be successfully modelled using a two-dimensional model, indicating that barrier effects dominate for these path geometries. Amplitude ratios along a third path, and the frequency-dependence of these ratios, are better simulated using a three-dimensional model that captures the out-of-plane diffractive effects around a prominent hill. The fourth path is poorly modelled using the three-dimensional model, which overpredicts acoustic amplitudes in this case. We hypothesise that this mismatch is likely to be due to a simplified description of the wind turbine source term. This study provides further observational confirmation that topographic interactions need to be considered when interpreting locally propagating infrasound, and shows that for harmonic narrowband sources a parabolic equation solver incorporating realistic boundary conditions provides an efficient method for simulating topographic interactions.

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Section: Discussionsupporting

confidence: 61%

Three-dimensional topographic effects on infrasound propagation across Ascension Island

Khodr

Green

Azarpeyvand

2022

Geophysical Journal International

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“…Extensive work over the past decade has demonstrated impact of topography on local infrasound observations through scattering and diffraction (Fee et al., 2017; Ishii et al., 2020; Kim & Lees, 2011, 2014; Kim et al., 2015; Lacanna & Ripepe, 2013, 2020; Maher et al., 2021; Matoza et al., 2009). Meteorological conditions and near‐vent winds can also strongly impact the observed infrasound signal (Fee & Garcés, 2007; Johnson et al., 2012).…”

Section: Discussionmentioning

confidence: 99%

Infrasound Radiation From Impulsive Volcanic Eruptions: Nonlinear Aeroacoustic 2D Simulations

et al. 2021

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Infrasound observations are increasingly used to constrain properties of volcanic eruptions. In order to better interpret infrasound observations, however, there is a need to better understand the relationship between eruption properties and sound generation. Here we perform two‐dimensional computational aeroacoustic simulations where we solve the compressible Navier‐Stokes equations for pure‐air with a large‐eddy simulation approximation. We simulate idealized impulsive volcanic eruptions where the exit velocity is specified and the eruption is pressure‐balanced with the atmosphere. Our nonlinear simulation results are compared with the commonly used analytical linear acoustics model of a compact monopole source radiating acoustic waves isotropically in a half space. The monopole source model matches the simulations for low exit velocities (<100 m/s or M0.3333em≈0.3333em0.3 where M is the Mach number); however, the two solutions diverge as the exit velocity increases with the simulations developing lower peak amplitude, more rapid onset, and anisotropic radiation with stronger infrasound signals recorded above the vent than on Earth's surface. Our simulations show that interpreting ground‐based infrasound observations with the monopole source model can result in an underestimation of the erupted volume for eruptions with sonic or supersonic exit velocities. We examine nonlinear effects and show that nonlinear effects during propagation are relatively minor for the parameters considered. Instead, the dominant nonlinear effect is advection by the complex flow structure that develops above the vent. This work demonstrates the need to consider anisotropic radiation patterns and jet dynamics when interpreting infrasound observations, particularly for eruptions with sonic or supersonic exit velocities.

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“…Extensive work over the past decade has demonstrated the significance of wavefield interactions with topography such as scattering and diffraction (Matoza et al 2009b;Kim & Lees 2011Kim et al 2015;Ishii et al 2020;Maher et al 2021). The availability of lowcost unmanned aerial vehicles and affordable structure-frommotion software has allowed more researchers to create high-resolution digital elevation models (DEMs) of volcanic edifices, which can be used for modeling infrasound propagation.…”

Section: Infrasound Propagationmentioning

confidence: 99%

Volcano infrasound: progress and future directions

Watson¹,

Iezzi

Toney

et al. 2022

Bull Volcanol

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Over the past two decades (2000–2020), volcano infrasound (acoustic waves with frequencies less than 20 Hz propagating in the atmosphere) has evolved from an area of academic research to a useful monitoring tool. As a result, infrasound is routinely used by volcano observatories around the world to detect, locate, and characterize volcanic activity. It is particularly useful in confirming subaerial activity and monitoring remote eruptions, and it has shown promise in forecasting paroxysmal activity at open-vent systems. Fundamental research on volcano infrasound is providing substantial new insights on eruption dynamics and volcanic processes and will continue to do so over the next decade. The increased availability of infrasound sensors will expand observations of varied eruption styles, and the associated increase in data volume will make machine learning workflows more feasible. More sophisticated modeling will be applied to examine infrasound source and propagation effects from local to global distances, leading to improved infrasound-derived estimates of eruption properties. Future work will use infrasound to detect, locate, and characterize moving flows, such as pyroclastic density currents, lahars, rockfalls, lava flows, and avalanches. Infrasound observations will be further integrated with other data streams, such as seismic, ground- and satellite-based thermal and visual imagery, geodetic, lightning, and gas data. The volcano infrasound community should continue efforts to make data and codes accessible and to improve diversity, equity, and inclusion in the field. In summary, the next decade of volcano infrasound research will continue to advance our understanding of complex volcano processes through increased data availability, sensor technologies, enhanced modeling capabilities, and novel data analysis methods that will improve hazard detection and mitigation.

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Evaluating the applicability of a screen diffraction approximation to local volcano infrasound

Cited by 15 publications

References 70 publications

Three-dimensional topographic effects on infrasound propagation across Ascension Island

Three-dimensional topographic effects on infrasound propagation across Ascension Island

Infrasound Radiation From Impulsive Volcanic Eruptions: Nonlinear Aeroacoustic 2D Simulations

Volcano infrasound: progress and future directions

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