The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Charles P. Ursenbach - One of the best experts on this subject based on the ideXlab platform.
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Anelasticity and Spherical-Wave AVO-modelling in VTI-media
2015Co-Authors: Arnim B. Haase, Charles P. UrsenbachAbstract:Anelasticity modifies VTI AVO responses. When reflection amplitude losses due to attenuation are compensated for by unit reflectivity scaling and spreading factor scaling, AVO-characteristics similar to the elastic situation are found. Q-factor dependence of Spherical Wave AVO is found to be strongest near critical angles. This Q-dependence, to some degree, mimics depth dependence of elastic comparisons
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Spherical Wave computational avo modelling in elastic and anelastic isotropic two layer media
69th EAGE Conference and Exhibition incorporating SPE EUROPEC 2007, 2007Co-Authors: Arnim B. Haase, Charles P. UrsenbachAbstract:Summary Compressional-Wave AVO responses and converted-Wave AVO responses in elastic and anelastic two-layer isotropic Class 1 models are investigated. These responses are computed by utilizing Zoeppritz reflection coefficients and the Weyl/Sommerfeld-integral. Spherical-Wave depth dependence for PP and PSv Class 1 models is found to be strongest near the critical angle. The constant-Q approximation is used to introduce anelastic effects. AVO responses of two-layer isotropic models are sensitive to anelasticity. This Q-factor dependence is strongest near critical
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Efficient Spherical-Wave AVO modeling
The Leading Edge, 2007Co-Authors: Charles P. Ursenbach, Arnim B. Haase, Jon DowntonAbstract:Point-source effects are becoming recognized as important in some long-offset AVO studies. In this article, we introduce the ideas of Spherical-Wave AVO, caused by point sources, and then present a new and simple way of calculating Spherical-Wave reflection coefficients.
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Spherical-Wave AVO-modelling in elastic VTI-media
2005Co-Authors: Arnim B. Haase, Charles P. UrsenbachAbstract:The AVO response of two-layer VTI models for AVO Class I is investigated. Graebner/Rueger reflection coefficients and the “Weyl-integral for anisotropic media” are utilized for the computation. Spherical Wave results are compared with the planeWave reflectivity. Depth dependence of Spherical Wave AVO is found to be strongest near critical angles, as was observed in the isotropic situation. Both C-Wave AVO and P-Wave AVO are more sensitive to changes in anisotropy than to changes in depth.
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An efficient method for calculating Spherical-Wave reflection coefficients
2004Co-Authors: Charles P. Ursenbach, Arnim B. HaaseAbstract:A method is presented for efficiently calculating the Spherical-Wave generalization of the Zoeppritz PP reflection coefficients. The main restriction is in choosing a particular form of Wavelet that allows for analytic integration over frequencies. This, combined with calculating only one time point instead of the entire time trace, results in calculations sufficiently rapid to be carried out interactively on the computer. The method is implemented both in MATLAB and as an interactive Java applet, and results are shown for an AVO Class I model. It is also shown that the calculation of Spherical-Wave reflection coefficients can, in practice, be cast as a weighted integral of a relatively small set of plane-Wave reflection coefficients, which may allow one to achieve still more efficient calculations.
Arnim B. Haase - One of the best experts on this subject based on the ideXlab platform.
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Anelasticity and Spherical-Wave AVO-modelling in VTI-media
2015Co-Authors: Arnim B. Haase, Charles P. UrsenbachAbstract:Anelasticity modifies VTI AVO responses. When reflection amplitude losses due to attenuation are compensated for by unit reflectivity scaling and spreading factor scaling, AVO-characteristics similar to the elastic situation are found. Q-factor dependence of Spherical Wave AVO is found to be strongest near critical angles. This Q-dependence, to some degree, mimics depth dependence of elastic comparisons
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Spherical Wave computational avo modelling in elastic and anelastic isotropic two layer media
69th EAGE Conference and Exhibition incorporating SPE EUROPEC 2007, 2007Co-Authors: Arnim B. Haase, Charles P. UrsenbachAbstract:Summary Compressional-Wave AVO responses and converted-Wave AVO responses in elastic and anelastic two-layer isotropic Class 1 models are investigated. These responses are computed by utilizing Zoeppritz reflection coefficients and the Weyl/Sommerfeld-integral. Spherical-Wave depth dependence for PP and PSv Class 1 models is found to be strongest near the critical angle. The constant-Q approximation is used to introduce anelastic effects. AVO responses of two-layer isotropic models are sensitive to anelasticity. This Q-factor dependence is strongest near critical
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Efficient Spherical-Wave AVO modeling
The Leading Edge, 2007Co-Authors: Charles P. Ursenbach, Arnim B. Haase, Jon DowntonAbstract:Point-source effects are becoming recognized as important in some long-offset AVO studies. In this article, we introduce the ideas of Spherical-Wave AVO, caused by point sources, and then present a new and simple way of calculating Spherical-Wave reflection coefficients.
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Spherical-Wave AVO-modelling in elastic VTI-media
2005Co-Authors: Arnim B. Haase, Charles P. UrsenbachAbstract:The AVO response of two-layer VTI models for AVO Class I is investigated. Graebner/Rueger reflection coefficients and the “Weyl-integral for anisotropic media” are utilized for the computation. Spherical Wave results are compared with the planeWave reflectivity. Depth dependence of Spherical Wave AVO is found to be strongest near critical angles, as was observed in the isotropic situation. Both C-Wave AVO and P-Wave AVO are more sensitive to changes in anisotropy than to changes in depth.
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An efficient method for calculating Spherical-Wave reflection coefficients
2004Co-Authors: Charles P. Ursenbach, Arnim B. HaaseAbstract:A method is presented for efficiently calculating the Spherical-Wave generalization of the Zoeppritz PP reflection coefficients. The main restriction is in choosing a particular form of Wavelet that allows for analytic integration over frequencies. This, combined with calculating only one time point instead of the entire time trace, results in calculations sufficiently rapid to be carried out interactively on the computer. The method is implemented both in MATLAB and as an interactive Java applet, and results are shown for an AVO Class I model. It is also shown that the calculation of Spherical-Wave reflection coefficients can, in practice, be cast as a weighted integral of a relatively small set of plane-Wave reflection coefficients, which may allow one to achieve still more efficient calculations.
Junichi Takada - One of the best experts on this subject based on the ideXlab platform.
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antenna de embedding in fdtd based radio propagation prediction by using Spherical Wave function
IEEE Transactions on Antennas and Propagation, 2015Co-Authors: Junichi Naganawa, Katsuyuki Haneda, Minseok Kim, Takahiro Aoyagi, Junichi TakadaAbstract:Finite-difference time-domain (FDTD) method is one of the promising approaches for the propagation prediction. However, since the computational domain includes both the antennas and the propagation environment, their coupling prevents evaluating individual contributions to the channel response. As a result, the simulation becomes always specific to the given antenna type or orientation and cannot be reused for other configurations. The simulation also requires the internal structure of the antenna which is often unavailable and/or difficult to be modeled. These problems can be addressed by antenna de-embeddeding which separately models the antenna and the propagation environment, hence the purpose of this paper. In particular, this paper proposes the implementation of Spherical-Wave-function (SWF) channel modeling using the FDTD method. Instead of modeling the real antenna structures inside the computational domain, the single-mode Spherical Wave source and the observation points are utilized. The Spherical Wave source is achieved by a cubical dipole array. The Spherical Wave source is first validated, including the investigation of the effects of cell and array size. The narrowband channel response synthesized by the proposed approach is then validated numerically through comparison with the transmission formula in free space and the conventional antenna-embedded simulation in the human shadowing environment as well.
Zhaoyun Zong - One of the best experts on this subject based on the ideXlab platform.
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Frequency-dependent Spherical-Wave nonlinear AVO inversion in elastic media
Geophysical Journal International, 2020Co-Authors: Guangsen Cheng, Xingyao Yin, Zhaoyun ZongAbstract:SUMMARY The plane-Wave reflection coefficient (PRC) plays a remarkable role in conventional amplitude variation with offset (AVO) analysis and inversion. Compared with the widely exploited PRC that breaks down at the near- and supercritical incidence angles, the Spherical-Wave reflection coefficient (SRC) can overcome the influence of wide-angle reflection and give an accurate description of the actual seismic Wave reflection phenomenon based on Spherical-Wave fronts. However, SRC is not widely used in AVO inversion due to its nonlinearity and computational complexity. In our study, the characteristics of frequency–depth-dependent monochromatic SRC are discussed and a novel three-parameter SRC is derived. Compared with the conventional six-parameter SRC, the novel three-parameter SRC improves the stability of Spherical-Wave AVO inversion. In addition, the concept of SRC within the Fresnel zone is proposed, and the accuracy of SRC within the Fresnel zone in the deep subsurface is tested. Finally, a nonlinear Spherical-Wave AVO inversion method for elastic media is proposed, which can make full use of all frequency components of Wavelet. The robustness of the proposed method is verified by the application on synthetic seismogram with white Gaussian noise. The feasibility and practicability of this method are verified by comparing the Spherical-Wave AVO inversion results with the filtered well logs at the known well location.
Takashi Fujikawa - One of the best experts on this subject based on the ideXlab platform.
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Theory of damping in forward scattering photoelectron diffraction due to thermal Spherical Wave effects
Journal of Electron Spectroscopy and Related Phenomena, 1998Co-Authors: Takashi Fujikawa, Kentaro Nakayama, Takumi YanagawaAbstract:Abstract Numerical calculations illustrate the importance of Spherical Wave effects in high energy ARXPS (Photoelectron Diffraction) spectra. In particular, Spherical Wave effects play an important role in the small-angle scatterings which predominate in ARXPS processes. In forward scattering both static and dynamical Spherical Wave effects play an important role. even in the high energy region.
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Theory of Spherical-Wave Debye-Waller Factors in Photoelectron Diffraction Spectra Compared with that in EXAFS
Journal De Physique Iv, 1997Co-Authors: Takashi Fujikawa, T. YanagawaAbstract:A new approach is applied to the analyses of thermal effects in ARXPS (photoelectron diffraction) spectra, where we include both Spherical Wave correction and anharmonic vibration effects. A partial summation technique is applied to get a plane Wave part and a Spherical Wave part(dynamical Spherical Wave effect ). Numerical calculations illustrate the importance of the Spherical Wave effects in high energy ARXPS spectra. In particular the Spherical Wave effects play an important role in the small-angle scatterings which predominate in the ARXPS processes. In comparison with the dynamical Spherical Wave effects in EXAFS those in ARXPS only reduce the intensities whereas the phase is unchanged.
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Spherical Wave effects on ARXPS Debye—Waller factors
Surface Science, 1996Co-Authors: T. Yanagawa, Takashi FujikawaAbstract:In this work we have applied a new approach developed by us to the analyses of thermal effects in ARXPS spectra, where we include both Spherical Wave correction and anharmonic vibration effects based on Brouder's Lie group formulas. We apply partial summation technique to get a plane Wave part which does not disappear even for large kR limit, and a Spherical Wave part which disappears for that limit. Numerical calculations illustrate the Spherical Wave effects in ARXPS spectra.
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Theory of anharmonic Debye-Waller factors in Spherical Wave EXAFS
Physica B: Condensed Matter, 1995Co-Authors: Takashi Fujikawa, Masaru Yimagawa, Takafumi MiyanagaAbstract:Abstract In this work we have developed a new approach to include both Spherical Wave correction and anharmonic vibration effects. The Spherical Wave correction disappears for large kR limit, but the plane Wave part has already Spherical Wave effects of photoelectron scattering in this formula.
