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

Volcanica ◽  
2021 ◽  
pp. 67-85
Author(s):  
Sean Maher ◽  
Robin Matoza ◽  
Catherine de Groot-Hedlin ◽  
Keehoon Kim ◽  
Kent Gee
Keyword(s):  
Acoustic Waves ◽  
Source Parameters ◽  
Computational Cost ◽  
Power Losses ◽  
Multiple Reflections ◽  
Constructive Interference ◽  
New Developments ◽  
Hazard Modeling ◽  
Prediction Capability ◽  
Thin Screen

Atmospheric acoustic waves from volcanoes at infrasonic frequencies (0.01–20 Hz) can be used to estimate source parameters for hazard modeling, but signals are often distorted by wavefield interactions with topography, even at local recording distances (<15 km). We present new developments toward a simple empirical approach to estimate attenuation by topographic diffraction at reduced computational cost. We investigate the applicability of a thin screen diffraction relationship developed by Maekawa [1968, doi: https://doi.org/10.1016/0003-682X(68)90020- 0]. We use a 2D axisymmetric finite-difference method to show that this relationship accurately predicts power losses for infrasound diffraction over an idealized kilometer-scale screen; thus validating the scaling to infrasonic wavelengths. However, the Maekawa relationship overestimates attenuation for realistic volcano topography (using Sakurajima Volcano as an example). The attenuating effect of diffraction may be counteracted by constructive interference of multiple reflections along concave volcano slopes. We conclude that the Maekawa relationship is insufficient as formulated for volcano infrasound, and suggest modifications that may improve the prediction capability.

Subsurface reflectivity estimation from imaging of primaries and multiples using amplitude-normalized separated wavefields

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. S101-S117 ◽  
Author(s):  
Alba Ordoñez ◽  
Walter Söllner ◽  
Tilman Klüver ◽  
Leiv J. Gelius
Keyword(s):  
Integral Equation ◽  
Fredholm Integral Equation ◽  
Computational Cost ◽  
Image Point ◽  
Point Location ◽  
Multiple Reflections ◽  
Frequency Space ◽  
Propagation Effects ◽  
The Matrix ◽  
Spatial Domains

Several studies have shown the benefits of including multiple reflections together with primaries in the structural imaging of subsurface reflectors. However, to characterize the reflector properties, there is a need to compensate for propagation effects due to multiple scattering and to properly combine the information from primaries and all orders of multiples. From this perspective and based on the wave equation and Rayleigh’s reciprocity theorem, recent works have suggested computing the subsurface image from the Green’s function reflection response (or reflectivity) by inverting a Fredholm integral equation in the frequency-space domain. By following Claerbout’s imaging principle and assuming locally reacting media, the integral equation may be reduced to a trace-by-trace deconvolution imaging condition. For a complex overburden and considering that the structure of the subsurface is angle-dependent, this trace-by-trace deconvolution does not properly solve the Fredholm integral equation. We have inverted for the subsurface reflectivity by solving the matrix version of the Fredholm integral equation at every subsurface level, based on a multidimensional deconvolution of the receiver wavefields with the source wavefields. The total upgoing pressure and the total filtered downgoing vertical velocity were used as receiver and source wavefields, respectively. By selecting appropriate subsets of the inverted reflectivity matrix and by performing an inverse Fourier transform over the frequencies, the process allowed us to obtain wavefields corresponding to virtual sources and receivers located in the subsurface, at a given level. The method has been applied on two synthetic examples showing that the computed reflectivity wavefields are free of propagation effects from the overburden and thus are suited to extract information of the image point location in the angular and spatial domains. To get the computational cost down, our approach is target-oriented; i.e., the reflectivity may only be computed in the area of most interest.

Farley Buneman instabilities in the Auroral region: Continuous kinetic and hybrid simulations.

2021 ◽  
Author(s):  
Enrique Rojas ◽  
David Hysell
Keyword(s):  
Computational Cost ◽  
Phase Speed ◽  
Auroral Region ◽  
Comprehensive Description ◽  
New Developments ◽  
Particle In Cell ◽  
New Methods ◽  
E Region ◽  
Non Local ◽  
Radar Measurements

&lt;p&gt;Farley-Buneman instabilities generate a spectrum of field-aligned plasma density irregularities in the E region. Although fully kinetic particle-in-cell simulations offer a comprehensive description of the underlying physics, its computational cost for studying non-local phenomena is tremendous. New methods based on hybrid and continuous approaches have to be explored to capture non-local physics.&lt;/p&gt;&lt;p&gt;In this work, we present new developments on a continuous solver of Farley-Buneman waves. We compare the performance of fully kinetic (continuous), hybrid, and fluid models. Furthermore, we investigate phase speed saturation, wave turning effects, and dominant wavelengths and assess how well these correspond to radar measurements. Finally, we describe some initial attempts at constructing simple surrogate models to capture the dominant microphysics of these simulations.&lt;/p&gt;

Migration with reduced artifacts from internal multiple reflections

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. A25-A29
Author(s):  
Lele Zhang
Keyword(s):  
Seismic Reflection ◽  
Computational Cost ◽  
Data Sets ◽  
Square Root ◽  
Multiple Reflections ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Recent Developments ◽  
Multiple Elimination

Migration of seismic reflection data leads to artifacts due to the presence of internal multiple reflections. Recent developments have shown that these artifacts can be avoided using Marchenko redatuming or Marchenko multiple elimination. These are powerful concepts, but their implementation comes at a considerable computational cost. We have derived a scheme to image the subsurface of the medium with significantly reduced computational cost and artifacts. This scheme is based on the projected Marchenko equations. The measured reflection response is required as input, and a data set with primary reflections and nonphysical primary reflections is created. Original and retrieved data sets are migrated, and the migration images are multiplied with each other, after which the square root is taken to give the artifact-reduced image. We showed the underlying theory and introduced the effectiveness of this scheme with a 2D numerical example.

scholarly journals Data-driven internal multiple elimination and its consequences for imaging: A comparison of strategies

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. S365-S372 ◽  
Author(s):  
Lele Zhang ◽  
Jan Thorbecke ◽  
Kees Wapenaar ◽  
Evert Slob
Keyword(s):  
Inverse Scattering ◽  
Computational Cost ◽  
Multiple Reflection ◽  
Data Driven ◽  
Transmission Losses ◽  
Multiple Reflections ◽  
Data Set ◽  
Numerical Examples ◽  
Inverse Scattering Series ◽  
Multiple Elimination

We have compared three data-driven internal multiple reflection elimination schemes derived from the Marchenko equations and inverse scattering series (ISS). The two schemes derived from Marchenko equations are similar but use different truncation operators. The first scheme creates a new data set without internal multiple reflections. The second scheme does the same and compensates for transmission losses in the primary reflections. The scheme derived from ISS is equal to the result after the first iteration of the first Marchenko-based scheme. It can attenuate internal multiple reflections with residuals. We evaluate the success of these schemes with 2D numerical examples. It is shown that Marchenko-based data-driven schemes are relatively more robust for internal multiple reflection elimination at a higher computational cost.

scholarly journals HXR photospheric footprints

2007 ◽  
Vol 3 (S247) ◽  
pp. 110-113
Author(s):  
J. C. Martínez-Oliveros ◽  
A.-C. Donea ◽  
P. S. Cally
Keyword(s):  
Solar Flares ◽  
Acoustic Waves ◽  
Neutral Line ◽  
Impulsive Phase ◽  
Coronal Loops ◽  
Direct Link ◽  
Constructive Interference ◽  
X Ray ◽  
Hydrodynamic Response ◽  
Relativistic Particles

AbstractWe have analysed the 6 mHz egression power signatures of some accoustically active X-class solar flares. During the impulsive phase these flares produced conspicuous seismic signatures which have kernel-like structures, mostly aligned with the neutral line of the host active region. The kernel-like structures show the effect of constructive interference of the acoustic waves emanating from the complex sources, suggesting motion of the acoustic sources. The co-aligment between the seismic signatures and the hard X-ray emission observed by RHESSI from the footpoints of the coronal loops suggests a direct link between relativistic particles accelerated during the flare and the hydrodynamic response of the photosphere during flares.

NEW DEVELOPMENTS IN THE TUNNELING AND TIME ANALYSIS OF LOW-ENERGY NUCLEAR PROCESSES

2010 ◽  
Vol 19 (05n06) ◽  
pp. 1212-1219 ◽  
Author(s):  
V. S. OLKHOVSKY ◽  
M. E. DOLINSKA ◽  
S. A. OMELCHENKO ◽  
M. V. ROMANIUK
Keyword(s):  
Three Dimensional ◽  
Low Energy ◽  
Quantum Mechanical ◽  
Time Analysis ◽  
Multiple Reflections ◽  
New Developments ◽  
L System ◽  
New Applications ◽  
Nuclear Processes

The new applications of the three-dimensional tunnelling and time analysis to low-energy nuclear processes are presented. The three-dimensional tunnelling is strictly quantum-mechanical and considers the internal multiple reflections. The time analysis of the nucleon-nucleons scattering near a resonance, distorted by the non-resonant background, does show the solution in the L -system of the paradox of the delay-advance in the C -system.

Parallel Architecture of Reconfigurable Hardware for Massive Output Active Noise Control

2019 ◽  
Vol 29 (03) ◽  
pp. 1950014
Author(s):  
Diego Mendez ◽  
David Arevalo ◽  
Diego Patino ◽  
Eduardo Gerlein ◽  
Ricardo Quintana
Keyword(s):  
Acoustic Waves ◽  
Noise Control ◽  
Reference Signal ◽  
Active Noise Control ◽  
Computational Cost ◽  
Main Idea ◽  
Parallel Architecture ◽  
Acceptable Error ◽  
Active Noise ◽  
Fxlms Algorithm

Filtered-x Least Mean Squares (FxLMS) is an algorithm commonly used for Active Noise Control (ANC) systems in order to cancel undesired acoustic waves from a sound source. There is a small number of hardware designs reported in the literature, that in turn only use one reference signal, one error signal and one output control signal. In this paper, it is proposed a 3-dimensional hardware-based version of the widely used FxLMS algorithm, using one reference microphone, 18 error microphones, one output and a FIR filter of 400[Formula: see text] order. The FxLMS algorithm was implemented in a Xilinx Artix 7 FPGA running at 25 MHz, which allowed to update the filter coefficients in 32.44[Formula: see text] s. The main idea behind this work is to propose a pipelined parallelized architecture to achieve processing times faster than real time for the filter coefficients update. The main contribution of this work is not the ANC technique itself, but rather the proposed hardware implementation that utilizes integer arithmetic, which provided an acceptable error when benchmarked with a software implementation. This parallel system allows a scalable implementation as an advantage of using FPGA without compromising the computational cost and, consequently, the latency.

scholarly journals Patched Green's function method applied to acoustic wave propagation in disordered media: an interdisciplinary approach

2020 ◽  
Vol 17 (5) ◽  
pp. 914-922
Author(s):  
Francisco A Moura ◽  
Wagner A Barbosa ◽  
Edwin F Duarte ◽  
Danyelle P Silva ◽  
Mauro S Ferreira ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Acoustic Wave ◽  
Green’S Function ◽  
Green's Function ◽  
Acoustic Waves ◽  
Structural Information ◽  
Computational Cost ◽  
Computational Time ◽  
Model Parameters ◽  
Large Matrix

Abstract Modern visualization can be formulated as inversion problems that aim to obtain structural information about a complex medium through wave excitations. However, without numerically efficient forward calculations, even state-of-the-art inversion procedures are too computationally intensive to implement. We adapt a method previously used to treat transport in electronic waveguides to describe acoustic wave motion in complex media with high gains in computational time. The method consists of describing the system as if it was made of disconnected parts that are patched together. By expressing the system in this manner, wave-propagation calculations that otherwise would involve a very large matrix can be done with considerably smaller matrices instead. In particular, by treating one of such patches as a target whose parameters are changeable, we are able to implement target-oriented optimization in which the model parameters can be continuously refined until the ideal result is reproduced. The so-called Patched Green's function (PGF) approach is mathematically exact and involves no approximations, thus improving the computational cost without compromising accuracy. Given the generality of our method, it can be applied to a wide variety of inversion problems. Here we apply it to the case of seismic modeling where acoustic waves are used to map the earth subsurface in order to identify and explore mineral resources. The technique is tested with realistic seismic models and compared to standard calculation methods. The reduction in computational complexity is remarkable and paves the way to treating larger systems with increasing accuracy levels.

scholarly journals Recent Developments and Applications of Acoustic Infrasound to Monitor Volcanic Emissions

2019 ◽  
Vol 11 (11) ◽  
pp. 1302 ◽  
Author(s):  
Silvio De Angelis ◽  
Alejandro Diaz-Moreno ◽  
Luciano Zuccarello
Keyword(s):  
Acoustic Waves ◽  
Risk Mitigation ◽  
Near Field ◽  
Source Parameters ◽  
Time History ◽  
Wave Theory ◽  
Volume Flow ◽  
Civil Aviation ◽  
Volcanic Emissions ◽  
Early Assessment

Volcanic ash is a well-known hazard to population, infrastructure, and commercial and civil aviation. Early assessment of the parameters that control the development and evolution of volcanic plumes is crucial to effective risk mitigation. Acoustic infrasound is a ground-based remote sensing technique—increasingly popular in the past two decades—that allows rapid estimates of eruption source parameters, including fluid flow velocities and volume flow rates of erupted material. The rate at which material is ejected from volcanic vents during eruptions, is one of the main inputs into models of atmospheric ash transport used to dispatch aviation warnings during eruptive crises. During explosive activity at volcanoes, the injection of hot gas-laden pyroclasts into the atmosphere generates acoustic waves that are recorded at local, regional and global scale. Within the framework of linear acoustic theory, infrasound sources can be modelled as multipole series, and acoustic pressure waveforms can be inverted to obtain the time history of volume flow at the vent. Here, we review near-field (<10 km from the vent) linear acoustic wave theory and its applications to the assessment of eruption source parameters. We evaluate recent advances in volcano infrasound modelling and inversion, and comment on the advantages and current limitations of these methods. We review published case studies from different volcanoes and show applications to new data that provide a benchmark for future acoustic infrasound studies.

40. Radio Astronomy

1982 ◽  
Vol 18 (1) ◽  
pp. 529-549
Author(s):  
G. Swarup
Keyword(s):  
Data Processing ◽  
Radio Astronomy ◽  
Present Report ◽  
Source Parameters ◽  
Radio Sources ◽  
Radio Telescopes ◽  
New Developments

This report covers surveys of radio sources, basic measurements of source parameters and new developments in radio telescopes, instrumental techniques and data processing. The period covered is approximately late 1978 to about August 1981. The results and conclusions of astronomical investigations based on measurements made through the radio window are included in the reports of other commissions, as relevant. Following the practice adopted in 1979, a circular was sent to the Presidents of 18 IAU Commissions and to all members of Commission 40 describing the proposed format of the present report and also identifying contact persons who could be consulted to avoid duplication and to ensure that radio astronomical results are adequately covered by various commissions. I am grateful to all concerned for providing the necessary coordination.

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