The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Matthew W Urban - One of the best experts on this subject based on the ideXlab platform.
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Dispersion Curve calculation in viscoelastic tissue mimicking materials using non parametric parametric and high resolution methods
Ultrasonics, 2021Co-Authors: Piotr Kijanka, Matthew W UrbanAbstract:Abstract Ultrasound shear wave elastography is a modality used for noninvasive, quantitative evaluation of soft tissue mechanical properties. A common way of exploring the tissue viscoelasticity is through analyzing the shear wave velocity Dispersion Curves. The variation of phase velocity with frequency or wavelength is called the Dispersion Curve. An increase of the available spectrum to be used for phase velocity estimation is meaningful for a tissue Dispersion analysis in vivo. A number of available methods for Dispersion relation estimation exist which can give diffuse results due the presence of noise in the measured data. In this work we compare six selected methods used for Dispersion Curve calculation in viscoelastic materials. Non-parametric, parametric and high-resolution methods were examined and compared. We tested selected methods on digital phantom data created using finite-difference-based method in tissue-mimicking viscoelastic media as well as on the experimental custom tissue-mimicking phantoms. In addition, we evaluated the algorithms with different levels of added white Gaussian noise to the shear wave particle velocity from numerical phantoms. Tests conducted showed that more advanced methods can offer better frequency resolution, and less variance than the fast Fourier transform. In addition, the non-parametric Blackman-Tukey approach exhibits similar performance and can be interchangeably used for shear wave phase velocity Dispersion Curves calculation.
Jianghai Xia - One of the best experts on this subject based on the ideXlab platform.
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offset and resolution of Dispersion Curve in multichannel analysis of surface waves masw
14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2001Co-Authors: Choon B Park, Richard D Miller, Jianghai XiaAbstract:Influence of offset-related parameters on the resolution of Dispersion Curve in multichannel analysis of surface waves (MASW) surveys is described from the theoretical perspective of the Dispersion Curve imaging method used during a normal implementation of MASW. The examined parameters include total number of channels (or traces), closest-to-source offset, receiver spacing, and total length of the receiver spread. The influences of different phase velocities and frequencies are also briefly described. It is shown that a larger total receiver spread length is always preferred to produce a higher resolution. This means that with a given number of channels available a greater receiver spacing is preferred as long as it does not cause a spatial aliasing problem. This shows that with MASW method the general notion that more channels are always better can be misleading.
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modal separation before Dispersion Curve extraction by masw method
14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2001Co-Authors: Julian Ivanov, Richard D Miller, Choon B Park, Jianghai XiaAbstract:Accurate extraction of Dispersion Curves is the most critical part with any surface-wave method. Although a multichannel method like Multichannel Analysis of Surface Waves (MASW) method proves most effective for this purpose, there are several acquisition parameters that need to be set properly for the optimal extraction. One of them requires a long range of receiver spread to separate phase velocity of one mode from those of other modes. Sometime, however, this requirement can not be met due to an unacceptable lateral inhomogeneity in the near-surface materials being surveyed and therefore multichannel records are often collected with a relatively short spread length. In this case the interference between the different modes of surface waves can be so severe that neither fundamental nor highermode Dispersion Curve can be extracted with a reliable confidence. In addition to this multimodal effect by surface waves, other types of seismic event such as channel (guided) waves can cause similar harmful effect during the analysis. When this occurs, a simple multichannel processing technique that mutes the interfering wavefields in the offset-time (x-t) domain can significantly enhance the resolution of multimodal Dispersion Curves. This is demonstrated by using both synthetic and real shot gathers.
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estimation of near surface shear wave velocity by inversion of rayleigh waves
Geophysics, 1999Co-Authors: Jianghai Xia, Richard D Miller, Choon B ParkAbstract:The shear‐wave (S-wave) velocity of near‐surface materials (soil, rocks, pavement) and its effect on seismic‐wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh‐wave phase velocity of a layered‐earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of Dispersion‐Curve sensitivity to earth properties. S-wave velocities are the dominant influence on a Dispersion Curve in a high‐frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high‐frequency range when using the Levenberg‐Marquardt and singular‐value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg‐Marquardt method. Synthetic examples demonstrated calculation efficiency and stability ...
Richard D Miller - One of the best experts on this subject based on the ideXlab platform.
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Dispersion Curve imaging considerations when using multichannel analysis of surface wave masw method
SAGEEP 2015 - 28th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2015Co-Authors: Julian Ivanov, Richard D Miller, Sarah L Morton, Shelby L PeterieAbstract:The multichannel analysis of surface wave (MASW) method can be an efficient tool for mapping the near-surface shear-wave velocity (Vs). Data acquisition, Dispersion-Curve imaging and estimations, inversion, and 2D visualization are distinct MASW components. Dispersion-Curves can be estimated on images that can be obtained by various transforms including converting seismic data from the time-space domain (i.e., t-x domain) into frequency–wave-number (i.e., f-k domain) by applying the Fourier transform to both time and space, Phase-velocity–frequency domain (e.g., Cf-f or f-v domain), slowness–frequency domain (i.e, p-f domain), phase-velocity–wavelength domain, etc. It has been our observation that while the mathematical link between such transforms is well known, the relationship between the corresponding images can be visually clarified for better comprehension. In this work we show the visual relationship between the f-k and the Cf-f domain images. We also demonstrate the visual effects of using fewer geophones (i.e., data along the space axis) with different spread sizes on the phase-velocity–frequency Dispersion-Curve imaging using surface-wave data with dominant single- and multi-mode surface-wave forms of expressions. These examples could help better understand and make more efficient use of the MASW data acquisition, analysis, and interpretation of final results.
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Dispersion Curve imaging nonuniqueness studies from multi channel analysis of surface waves masw using synthetic seismic data
Seg Technical Program Expanded Abstracts, 2013Co-Authors: Julian Ivanov, Tyler J Schwenk, Richard D Miller, Shelby L PeterieAbstract:Summary We use the multi-channel analysis of surface waves (MASW) method to analyze synthetic seismic data calculated from models that produce very similar high-velocity Dispersion Curve gradients at low frequencies. The MASW DispersionCurve images of the Rayleigh wave were obtained from data calculated using simple layered models with high (2-layer) and gradual (10-layer) shear-wave velocity (Vs) vertical gradients. The tests demonstrated that, for most of the frequency range, the corresponding Dispersion-Curve images are near identical with a high-velocity-gradient along low frequencies (HVGLF). The HVGLF trend obtained from the 2-layer model is a result of fundamental-mode Rayleigh-wave transitioning into the first higher mode, a ‘mode kissing.’ The HVGLF trend obtained from the 10-layer model is a result of only the fundamental-mode Rayleigh wave. It was observed that such nonuniqueness can lead to erroneous interpretation of Dispersion events and consequent Vs inversion results. Further analysis showed that Dispersion Curve image patterns differ at relatively very low and very high frequency ranges. As a result, it was concluded that it might be possible to obtain evidence of how to interpret HVGLF Dispersion Curve images by observing specific patterns that fall outside the main HVGLF Dispersion-Curve feature at lower and higher frequencies.
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offset and resolution of Dispersion Curve in multichannel analysis of surface waves masw
14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2001Co-Authors: Choon B Park, Richard D Miller, Jianghai XiaAbstract:Influence of offset-related parameters on the resolution of Dispersion Curve in multichannel analysis of surface waves (MASW) surveys is described from the theoretical perspective of the Dispersion Curve imaging method used during a normal implementation of MASW. The examined parameters include total number of channels (or traces), closest-to-source offset, receiver spacing, and total length of the receiver spread. The influences of different phase velocities and frequencies are also briefly described. It is shown that a larger total receiver spread length is always preferred to produce a higher resolution. This means that with a given number of channels available a greater receiver spacing is preferred as long as it does not cause a spatial aliasing problem. This shows that with MASW method the general notion that more channels are always better can be misleading.
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modal separation before Dispersion Curve extraction by masw method
14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2001Co-Authors: Julian Ivanov, Richard D Miller, Choon B Park, Jianghai XiaAbstract:Accurate extraction of Dispersion Curves is the most critical part with any surface-wave method. Although a multichannel method like Multichannel Analysis of Surface Waves (MASW) method proves most effective for this purpose, there are several acquisition parameters that need to be set properly for the optimal extraction. One of them requires a long range of receiver spread to separate phase velocity of one mode from those of other modes. Sometime, however, this requirement can not be met due to an unacceptable lateral inhomogeneity in the near-surface materials being surveyed and therefore multichannel records are often collected with a relatively short spread length. In this case the interference between the different modes of surface waves can be so severe that neither fundamental nor highermode Dispersion Curve can be extracted with a reliable confidence. In addition to this multimodal effect by surface waves, other types of seismic event such as channel (guided) waves can cause similar harmful effect during the analysis. When this occurs, a simple multichannel processing technique that mutes the interfering wavefields in the offset-time (x-t) domain can significantly enhance the resolution of multimodal Dispersion Curves. This is demonstrated by using both synthetic and real shot gathers.
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estimation of near surface shear wave velocity by inversion of rayleigh waves
Geophysics, 1999Co-Authors: Jianghai Xia, Richard D Miller, Choon B ParkAbstract:The shear‐wave (S-wave) velocity of near‐surface materials (soil, rocks, pavement) and its effect on seismic‐wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh‐wave phase velocity of a layered‐earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of Dispersion‐Curve sensitivity to earth properties. S-wave velocities are the dominant influence on a Dispersion Curve in a high‐frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high‐frequency range when using the Levenberg‐Marquardt and singular‐value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg‐Marquardt method. Synthetic examples demonstrated calculation efficiency and stability ...
Choon B Park - One of the best experts on this subject based on the ideXlab platform.
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offset and resolution of Dispersion Curve in multichannel analysis of surface waves masw
14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2001Co-Authors: Choon B Park, Richard D Miller, Jianghai XiaAbstract:Influence of offset-related parameters on the resolution of Dispersion Curve in multichannel analysis of surface waves (MASW) surveys is described from the theoretical perspective of the Dispersion Curve imaging method used during a normal implementation of MASW. The examined parameters include total number of channels (or traces), closest-to-source offset, receiver spacing, and total length of the receiver spread. The influences of different phase velocities and frequencies are also briefly described. It is shown that a larger total receiver spread length is always preferred to produce a higher resolution. This means that with a given number of channels available a greater receiver spacing is preferred as long as it does not cause a spatial aliasing problem. This shows that with MASW method the general notion that more channels are always better can be misleading.
-
modal separation before Dispersion Curve extraction by masw method
14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 2001Co-Authors: Julian Ivanov, Richard D Miller, Choon B Park, Jianghai XiaAbstract:Accurate extraction of Dispersion Curves is the most critical part with any surface-wave method. Although a multichannel method like Multichannel Analysis of Surface Waves (MASW) method proves most effective for this purpose, there are several acquisition parameters that need to be set properly for the optimal extraction. One of them requires a long range of receiver spread to separate phase velocity of one mode from those of other modes. Sometime, however, this requirement can not be met due to an unacceptable lateral inhomogeneity in the near-surface materials being surveyed and therefore multichannel records are often collected with a relatively short spread length. In this case the interference between the different modes of surface waves can be so severe that neither fundamental nor highermode Dispersion Curve can be extracted with a reliable confidence. In addition to this multimodal effect by surface waves, other types of seismic event such as channel (guided) waves can cause similar harmful effect during the analysis. When this occurs, a simple multichannel processing technique that mutes the interfering wavefields in the offset-time (x-t) domain can significantly enhance the resolution of multimodal Dispersion Curves. This is demonstrated by using both synthetic and real shot gathers.
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estimation of near surface shear wave velocity by inversion of rayleigh waves
Geophysics, 1999Co-Authors: Jianghai Xia, Richard D Miller, Choon B ParkAbstract:The shear‐wave (S-wave) velocity of near‐surface materials (soil, rocks, pavement) and its effect on seismic‐wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh‐wave phase velocity of a layered‐earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of Dispersion‐Curve sensitivity to earth properties. S-wave velocities are the dominant influence on a Dispersion Curve in a high‐frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high‐frequency range when using the Levenberg‐Marquardt and singular‐value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg‐Marquardt method. Synthetic examples demonstrated calculation efficiency and stability ...
Piotr Kijanka - One of the best experts on this subject based on the ideXlab platform.
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Dispersion Curve calculation in viscoelastic tissue mimicking materials using non parametric parametric and high resolution methods
Ultrasonics, 2021Co-Authors: Piotr Kijanka, Matthew W UrbanAbstract:Abstract Ultrasound shear wave elastography is a modality used for noninvasive, quantitative evaluation of soft tissue mechanical properties. A common way of exploring the tissue viscoelasticity is through analyzing the shear wave velocity Dispersion Curves. The variation of phase velocity with frequency or wavelength is called the Dispersion Curve. An increase of the available spectrum to be used for phase velocity estimation is meaningful for a tissue Dispersion analysis in vivo. A number of available methods for Dispersion relation estimation exist which can give diffuse results due the presence of noise in the measured data. In this work we compare six selected methods used for Dispersion Curve calculation in viscoelastic materials. Non-parametric, parametric and high-resolution methods were examined and compared. We tested selected methods on digital phantom data created using finite-difference-based method in tissue-mimicking viscoelastic media as well as on the experimental custom tissue-mimicking phantoms. In addition, we evaluated the algorithms with different levels of added white Gaussian noise to the shear wave particle velocity from numerical phantoms. Tests conducted showed that more advanced methods can offer better frequency resolution, and less variance than the fast Fourier transform. In addition, the non-parametric Blackman-Tukey approach exhibits similar performance and can be interchangeably used for shear wave phase velocity Dispersion Curves calculation.