On unified dual fields and Einstein deconvolution

Geophysics ◽  
2000 ◽  
Vol 65 (1) ◽  
pp. 293-303 ◽  
Author(s):  
Dan Loewenthal ◽  
Enders A. Robinson

In many physical phenomena, the laws governing motion can be looked at as the relationship between unified dual fields which are continuous in time and space. Both fields are activated by a single source. The most notable example of such phenomena is electromagnetism, in which the dual fields are the electric field and the magnetic field. Another example is acoustics, in which the dual fields are the particle‐velocity field and the pressure field. The two fields are activated by the same source and satisfy two first‐order partial differential equations, such as those obtained by Newton’s laws or Maxwell’s equations. These equations are symmetrical in time and space, i.e., they obey the same wave equation, which differs only in the interface condition changing sign. The generalization of the Einstein velocity addition equation to a layered system explains how multiple reflections are generated. This result shows how dual sensors at a receiver point at depth provide the information required for a new deconvolution method. This method is called Einstein deconvolution in honor of Albert Einstein. Einstein deconvolution requires measurements of the pressure signal, the particle velocity signal, and the rock impedance, all at the receiver point. From these measurements, the downgoing and upgoing waves at the receiver are computed. Einstein deconvolution is the process of deconvolving the upgoing wave by the downgoing wave. Knowledge of the source signature is not required. Einstein deconvolution removes the unknown source signature and strips off the effects of all the layers above the receiver point. Specifically, the output of Einstein deconvolution is the unit‐impulse reflection response of the layers below the receiver point. Compared with the field data, the unit‐impulse reflection response gives a much clearer picture of the deep horizons, a desirable result in all remote detection problems. In addition, the unit‐impulse reflection response is precisely the input required to perform dynamic deconvolution. Dynamic deconvolution yields the reflectivity (i.e., reflection‐ coefficient series) of the interfaces below the receiver point. Alternatively, predictive deconvolution can be used instead of dynamic deconvolution.

2013 ◽  
Vol 341-342 ◽  
pp. 601-604
Author(s):  
Di Xiao ◽  
Lan Yue Zhang

Water-entry signal was important to broadcast the water-entry object. The vector sensor could gain the pressure and particle velocity signal, so the azimuth angle of water-entry signal could be estimated by single vector sensor. The complex sound intensity method was applied in vector signal processing in azimuth estimation. The estimated deviation in different SNR was give out via simulating experiment. The method was used in the experiment on the lake and was proved to be effective.


2008 ◽  
Vol 16 (04) ◽  
pp. 563-576 ◽  
Author(s):  
MAJID NABAVI ◽  
M. H. KAMRAN SIDDIQUI ◽  
JAVAD DARGAHI

Combination of a fourth-order Padé compact finite difference discretization in space and a fourth-order Runge–Kutta time stepping scheme is shown to yield an effective method for solving highly nonlinear standing waves in a thermoviscous medium. This accurate and fast-solver numerical scheme can predict the pressure, particle velocity, and density along the standing wave resonator filled with a thermoviscous fluid from linear to strongly nonlinear levels of the excitation amplitude. The stability analysis is performed to determine the stability region of the scheme. Beside the fourth-order accuracy in both time and space, another advantage of the given numerical scheme is that no additional attenuation is required to get numerical stability. As it is well known, the results show that the pressure and particle velocity waveforms for highly nonlinear waves are significantly different from that of the linear waves, in both time and space. For highly nonlinear waves, the results also indicate the presence of a wavefront that travels along the resonator with very high pressure and velocity gradients. Two gases, air and CO 2, are considered. It is observed that the slopes of the traveling velocity and pressure gradients are higher for CO 2 than those for air. For highly nonlinear waves, the results also indicate the higher asymmetry in pressure for CO 2 than that for air.


Author(s):  
Yao-Chong Sun ◽  
Wei Zhang ◽  
Hengxin Ren ◽  
Xueyang Bao ◽  
Jian-Kuan Xu ◽  
...  

ABSTRACT The curvilinear-grid finite-difference method (FDM), which uses curvilinear coordinates to discretize the nonplanar interface geometry, is extended to simulate acoustic and seismic-wave propagation across the fluid–solid interface at the sea bottom. The coupled acoustic velocity-pressure and elastic velocity-stress formulation that governs wave propagation in seawater and solid earth is expressed in curvilinear coordinates. The formulation is solved on a collocated grid by alternative applications of forward and backward MacCormack finite difference within a fourth-order Runge–Kutta temporal integral scheme. The shape of a fluid–solid interface is discretized by a curvilinear grid to enable a good fit with the topographic interface. This good fit can obtain a higher numerical accuracy than the staircase approximation in the conventional FDM. The challenge is to correctly implement the fluid–solid interface condition, which involves the continuity of tractions and the normal component of the particle velocity, and the discontinuity (slipping) of the tangent component of the particle velocity. The fluid–solid interface condition is derived for curvilinear coordinates and explicitly implemented by a domain-decomposition technique, which splits a grid point on the fluid–solid interface into one grid point for the fluid wavefield and another one for the solid wavefield. Although the conventional FDM that uses effective media parameters near the fluid–solid interface to implicitly approach the boundary condition conflicts with the fluid–solid interface condition. We verify the curvilinear-grid FDM by conducting numerical simulations on several different models and compare the proposed numerical solutions with independent solutions that are calculated by the Luco-Apsel-Chen generalized reflection/transmission method and spectral-element method. Besides, the effects of a nonplanar fluid–solid interface and fluid layer on wavefield propagation are also investigated in a realistic seafloor bottom model. The proposed algorithm is a promising tool for wavefield propagation in heterogeneous media with a nonplanar fluid–solid interface.


Author(s):  
R. T. Mullins ◽  
David Anzalone ◽  
Ben Page

In 1969, T.F. Torrance published Space, Time, and Incarnation. This brought together recent work in philosophy and science on the nature of space and time in order to explore the implications for theology. Torrance’s theology engaged with the scientific thought of Albert Einstein and James Clerk Maxwell, as well as the temporal logic of A.N. Prior. The influence of this work on subsequent Christian theology cannot be overstated. Yet, a great deal has changed since 1969, and most contemporary discussions in systematic theology show little awareness of recent advancements in the metaphysics of time and space.


2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Lanyue Zhang ◽  
Di Wu ◽  
Xue Han ◽  
Zhongrui Zhu

Feature extraction method using Mel frequency cepstrum coefficients (MFCC) based on acoustic vector sensor is researched in the paper. Signals of pressure are simulated as well as particle velocity of underwater target, and the features of underwater target using MFCC are extracted to verify the feasibility of the method. The experiment of feature extraction of two kinds of underwater targets is carried out, and these underwater targets are classified and recognized by Backpropagation (BP) neural network using fusion of multi-information. Results of the research show that MFCC, first-order differential MFCC, and second-order differential MFCC features could be used as effective features to recognize those underwater targets and the recognition rate, which using the particle velocity signal is higher than that using the pressure signal, could be improved by using fusion features.


Geophysics ◽  
1983 ◽  
Vol 48 (3) ◽  
pp. 400-401
Author(s):  
Edward Szaraniec

The paper deals with the decomposition of the impulsive reflection seismogram into progressively delayed generalized primary wavelets. This decomposition serves to examine the patterns of primary and multiple reflections arising from the addition of a deeper interface to the layered system. Each of the generalized primary wavelets originates from a layered system augmented by a single deeper layer.


Geophysics ◽  
1980 ◽  
Vol 45 (11) ◽  
pp. 1697-1705 ◽  
Author(s):  
Peter Hubral ◽  
Sven Treitel ◽  
Paul R. Gutowski

The normal incidence unit impulse reflection response of a perfectly stratified medium is expressible as an autoregressive‐moving average (ARMA) model. In this representation, the autoregressive (AR) component describes the multiple patterns generated within the medium. The moving average (MA) component, on the other hand, bears a simple relation to the sequence of reflection coefficients (i.e., primaries only) of the layered structure. An alternate representation of the reflection response can be formulated in terms of a superposition of purely AR time‐varying minimum‐delay wavelets. Each successive addition of a deeper interface to the layered system gives rise to an AR wavelet whose leading term is equal to the magnitude of the primary reflection originating at this interface. We accordingly call these wavelets “generalized primaries.” The AR component of every generalized primary contains only those multiple reflections that arise from the addition of its particular interface to the layered medium.


1977 ◽  
Vol 36 ◽  
pp. 191-215
Author(s):  
G.B. Rybicki

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.


Author(s):  
George C. Ruben ◽  
Merrill W. Shafer

Traditionally ceramics have been shaped from powders and densified at temperatures close to their liquid point. New processing methods using various types of sols, gels, and organometallic precursors at low temperature which enable densificatlon at elevated temperatures well below their liquidus, hold the promise of producing ceramics and glasses of controlled and reproducible properties that are highly reliable for electronic, structural, space or medical applications. Ultrastructure processing of silicon alkoxides in acid medium and mixtures of Ludox HS-40 (120Å spheres from DuPont) and Kasil (38% K2O &62% SiO2) in basic medium have been aimed at producing materials with a range of well defined pore sizes (∼20-400Å) to study physical phenomena and materials behavior in well characterized confined geometries. We have studied Pt/C surface replicas of some of these porous sol-gels prepared at temperatures below their glass transition point.


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