SPECTRA OF WATER REVERBERATIONS FOR PRIMARY AND MULTIPLE REFLECTIONS

Geophysics ◽  
1972 ◽  
Vol 37 (5) ◽  
pp. 788-796 ◽  
Author(s):  
John Pflueger
Keyword(s):  
Reflection Coefficient ◽  
Seismic Event ◽  
Theoretical Study ◽  
Water Layer ◽  
Multiple Reflection ◽  
Multiple Reflections ◽  
Quick Method ◽  
Sea Floor ◽  
Marine Data ◽  
Amplitude Characteristics

A theoretical study shows that passage of a seismic event through the water‐layer filter imposes amplitude characteristics on the resultant reverberating event which are independent of whether the event is a primary reflection or a multiple reflection. The phase characteristics of each order of event are, however, different. It is also shown that the reverberating sequence from a multiple reflection can be “whitened” by deconvolution but will still exhibit ringing. This phenomenon explains why some marine data, containing dominantly multiple reflections, are not amenable to deringing using standard deconvolution approaches. In addition, a quick method of obtaining the approximate reflection coefficient of the sea floor is derived.

A MARINE SEISMIC MODEL

Geophysics ◽  
1956 ◽  
Vol 21 (2) ◽  
pp. 320-336 ◽  
Author(s):  
George P. Sarrafian
Keyword(s):  
Water Layer ◽  
Multiple Reflection ◽  
Air Bubbles ◽  
Seismic Model ◽  
Multiple Reflections ◽  
Marine Seismic ◽  
Search For Information

A model for the study of marine seismic phenomena is described. Study of multiple‐reflection phenomena forms the basis for the course of experiments. It is shown that the multiple‐reflection phenomenon of a disturbance with slowly decaying amplitude may be duplicated in the model. Multiple‐reflection problems are studied in which the bottom of the water layer is tilted or thin. A mass of air bubbles is shown to be of use in attenuating multiple reflections. The possible application of the marine model in a search for information about certain problems in field prospecting is suggested.

Deep‐water peg legs and multiples: Emulation and suppression

Geophysics ◽  
1986 ◽  
Vol 51 (12) ◽  
pp. 2177-2184 ◽  
Author(s):  
J. R. Berryhill ◽  
Y. C. Kim
Keyword(s):  
Wave Equation ◽  
Seismic Data ◽  
Water Layer ◽  
Original Data ◽  
Equation Method ◽  
Multiple Reflections ◽  
Step Method ◽  
Arrival Times ◽  
Sea Floor ◽  
Water Bottom

This paper discusses a two‐step method for predicting and attenuating multiple and peg‐leg reflections in unstacked seismic data. In the first step, an (observed) seismic record is extrapolated through a round‐trip traversal of the water layer, thus creating an accurate prediction of all possible multiples. In the second step, the record containing the predicted multiples is compared with and subtracted from the original. The wave‐equation method employed to predict the multiples takes accurate account of sea‐floor topography and so requires a precise water‐bottom profile as part of the input. Information about the subsurface below the sea floor is not required. The arrival times of multiple reflections are reproduced precisely, although the amplitudes are not accurate, and the sea floor is treated as a perfect reflector. The comparison step detects the similarities between the computed multiples and the original data, and estimates a transfer function to equalize the amplitudes and account for any change in waveform caused by the sea‐floor reflector. This two‐step wave‐equation method is effective even for dipping sea floors and dipping subsurface reflectors. It does not depend upon any assumed periodicity in the data or upon any difference in stacking velocity between primaries and multiples. Thus it is complementary to the less specialized methods of multiple suppression.

NOTES ON MULTIPLE REFLECTIONS

Geophysics ◽  
1948 ◽  
Vol 13 (1) ◽  
pp. 55-56
Author(s):  
Dean Walling
Keyword(s):  
Multiple Reflection ◽  
Large Percentage ◽  
Multiple Reflections ◽  
Reflection Theory ◽  
Proper Interpretation

Since the inception of the reflection seismograph, apparent reflections have been observed from time to time, which for one reason or another, do not meet the requirements of normal reflections from interfaces in the sedimentary section. Various theories have served to explain and allow the proper interpretation of a large percentage of these spurious energies. Among these is the multiple‐reflection theory which has proven to be applicable in many cases.

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.

Multiple Reflection Effect on Spin-Transfer Torque Dynamics in Spin Valves with a Single or Dual Polarizer

SPIN ◽  
2015 ◽  
Vol 05 (01) ◽  
pp. 1550003 ◽  
Author(s):  
Weiwei Zhu ◽  
Zongzhi Zhang ◽  
Jianwei Zhang ◽  
Yaowen Liu
Keyword(s):  
Spin Valve ◽  
Spin Transfer Torque ◽  
Multiple Reflection ◽  
Spin Transfer ◽  
Reflection Effect ◽  
Multiple Reflections ◽  
Applied Current ◽  
Negative Current ◽  
Ferromagnetic Layers ◽  
Scattering Matrix Method

In this paper, spin-dependent multiple reflection effect on spin-transfer torque (STT) has been theoretically and numerically studied in a spin valve nanopillar with a single or dual spin-polarizer. By using a scattering matrix method, we formulate an analytical expression of STT that contains the multiple interfacial reflection effect. It is found that the multiple reflections could enhance the STT efficiency and reduce the critical switching current. The STT efficiency depends on the spin polarization of both the free layer and polarizer. In the nanopillars with a dual spin polarizer, the multiple reflections would cause an asymmetric frequency dependence on the applied current, albeit exactly the same parameters are used in all three ferromagnetic layers, indicating that the frequency in the negative current varies much faster than that in the positive case.

Removal of water‐layer multiples from multicomponent sea‐bottom data

Geophysics ◽  
1999 ◽  
Vol 64 (3) ◽  
pp. 838-851 ◽  
Author(s):  
Are Osen ◽  
Lasse Amundsen ◽  
Arne Reitan
Keyword(s):  
Vertical Velocity ◽  
Water Layer ◽  
Real Data ◽  
Physical Principle ◽  
Sea Floor ◽  
Numerical Tests ◽  
Sea Bottom ◽  
Marine Source ◽  
Suppression Technique ◽  
Fundamental Physical

A method for suppressing water‐layer multiples in multicomponent sea‐floor measurements is presented. The multiple suppression technique utilizes the concept of wavefield separation into upgoing and downgoing modes just below the sea floor for eliminating the sea‐floor ghost, the sea‐surface ghost, and the accompanying water‐layer reverberations. The theory applies to each of the recorded components: pressure, vertical velocity, and horizontal velocities. The fundamental physical principle for the multiple suppression technique rests on identifying these multiples as downgoing waves just below the sea floor, while the primaries of interest arriving from the subsurface are upgoing waves. White presented this realization for the pressure component three decades ago; hence, the theory for the velocity field is an extension of the theory. In this paper, the theory is derived for an experiment with a marine source in the water layer above a locally flat, elastic sea floor with known elastic parameters. The method is otherwise multidimensional and operates on a shot‐to‐shot basis; hence, it is computationally fast. Aside from this, we show that this demultiple method removes the strongest multiples in sea‐floor data without knowledge of the source wavelet. Synthetic and real data examples are provided to illustrate the application of the algorithms to the pressure, in‐line velocity, and vertical velocity components. The numerical tests show that strong multiples have been attenuated on the pressure and the velocity recordings, producing promising results.

Data‐driven adaptive decomposition of multicomponent seabed recordings

Geophysics ◽  
2004 ◽  
Vol 69 (5) ◽  
pp. 1329-1337 ◽  
Author(s):  
Remco Muijs ◽  
Johan O. A. Robertsson ◽  
Klaus Holliger
Keyword(s):  
Water Layer ◽  
P Wave ◽  
Data Driven ◽  
Minimal Amount ◽  
S Wave ◽  
Sea Floor ◽  
Decomposition Scheme ◽  
Wave Potential ◽  
Dual Sensor ◽  
Adaptive Decomposition

Dual‐sensor (hydrophone and three‐component geophone) data recorded on the sea floor allow the elastic wavefield to be decomposed into its upgoing and downgoing P‐ and S‐wave components. Most decomposition algorithms require accurate knowledge of the elastic properties of the sea floor in the vicinity of the receivers and properly calibrated sensors, in order for the data to be a faithful vector representation of the ground motion. We present a multistep adaptive decomposition scheme that provides the necessary information directly from the data by imposing constraints on intermediate decomposition results. The proposed scheme requires no a priori information and only a minimal amount of user‐defined input, thus allowing multicomponent data to be decomposed in an automated data‐driven fashion. The performance of the technique is illustrated using seabed data acquired in the North Sea with prototype single sensors (multicomponent geophones individually sampled). Realistic sea floor properties and sensor calibration operators are obtained, and elastic decomposition of the calibrated data generally yields good results. Dominant water‐layer reverberations are successfully attenuated and primary reflections are substantially enhanced in the computed upgoing P‐wave potential just below the sea floor. In contrast, the result for the upgoing S‐wave potential is somewhat less convincing; although the energy of water‐layer multiples is substantially reduced, notable amounts of undesired multiple energy remain in this section after decomposition, particularly at high offsets. These imperfections may point to inaccuracies in the parametrization of the sea floor or remaining inaccuracies in the vector fidelity of the horizontal geophone recordings. Nevertheless, the results obtained with the extended data‐driven decomposition scheme are at least comparable to previously published results.

SOME EXPERIMENTS ON MULTIPLE REFLECTION CANCELLATION

Geophysics ◽  
1965 ◽  
Vol 30 (6) ◽  
pp. 1085-1093 ◽  
Author(s):  
Daniel Silverman ◽  
N. R. Sparks
Keyword(s):  
Noise Level ◽  
Multiple Reflection ◽  
Multiple Reflections ◽  
Near Surface ◽  
High Noise ◽  
Precise Information ◽  
High Noise Level ◽  
The Earth ◽  
Primary Signal ◽  
Seismic Records

One of the most promising methods of identification or cancellation of multiple reflections on seismic records involves the calculation of synthetic records with all primaries and multiples, and the matching of the synthetic record with the field record. Such matching suffers today from the lack of precise information about the velocities and densities of the formations, dips of beds nonvertical transmission, etc. One possibility of improving this match involves the use of the earth itself as the “synthetic record computer.” In this process, the upcoming (or downgoing) primary signals are fed back into the earth with a vibrator in proper amplitude and phase to create a synthetic record of multiples only, which should match the multiples on the field record. Of course, only those multiple reflections which include a downward reflection from beds above the primary signal detectors will be included in the synthetic record of multiples only. The paper reports two experimental programs. One was carried out on an analog network to simulate the near‐surface and deeper formations, with means to feed back the upcoming signals in proper timing and polarity to cancel the multiples. These experiments indicated the theoretical workability of the process. The second program of experiments involved the use of a vertical spread to detect the upcoming and downgoing signals, and the use of a hydraulic vibrator to impress those signals back into the earth. These experiments were not conclusive because of insufficient power in the vibrator and high noise level. However, they indicated possible ways in which these limitations might be reduced, and the method applied to routine field operations.

Model‐based removal of water‐layer multiple reflections

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1816-1827 ◽  
Author(s):  
Guochun Lu ◽  
Bjørn Ursin ◽  
Jan Lutro
Keyword(s):  
Water Layer ◽  
Computationally Efficient ◽  
Multiple Reflections ◽  
Model Based ◽  
The North ◽  
Sea Bottom ◽  
Receiver Array ◽  
Sea Bed ◽  
Reflectivity Function ◽  
Calculated Amplitude

We have developed a procedure to attenuate water‐layer multiple reflections. We estimate the sea‐bottom reflectivity function and use it plus calculated amplitude functions to model all order water‐layer multiple reflections, taking into account both amplitude and waveform shape. We model the primary and multiple reflections from the sea bottom in the frequency‐slowness domain. The amplitude function in the data modeling includes the source directivity function, source ghost response, receiver array directivity function, receiver ghost response, and offset‐dependent geometrical spreading. For small offsets we can assume that the seabed reflectivity depends only on frequency, and it is estimated using a least‐squares algorithm. An unknown scaling constant in the data is estimated using the amplitude of the primary and first multiple reflection from the sea bed. The composite sea‐bottom reflectivity is estimated as a function of frequency for each common midpoint (CMP) position. We apply the algorithm to high‐resolution seismic data from the North Sea. The modelled data match the recorded data well, and the estimated primary reflectivity is more geologically meaningful than the stacked trace. By comparison with Radon transform multiple removal applied to the same data, the model‐based method was more computationally efficient and left less residual multiple energy.

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