Comparison of two approaches to water layer multiple attenuation by wave field extrapolation

1987 ◽  
Author(s):  
Lars Sonneland ◽  
Lars E. Berg
Keyword(s):  
Wave Field ◽  
Water Layer ◽  
Multiple Attenuation

Attenuation of complex water‐bottom multiples by wave‐equation‐based prediction and subtraction

Geophysics ◽  
1988 ◽  
Vol 53 (12) ◽  
pp. 1527-1539 ◽  
Author(s):  
J. Wendell Wiggins
Keyword(s):  
Wave Field ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Water Layer ◽  
Lateral Position ◽  
Multiple Reflections ◽  
Multiple Attenuation ◽  
Predictive Method ◽  
Marine Seismic ◽  
Water Bottom

Multiple reflections that are generated by the water bottom in marine seismic data can be predicted by a combination of numerical wave extrapolation through the water layer and estimation of the water‐bottom reflectivity. Attenuation of the multiples occurs when the predicted wave field is subtracted from the original record. I derive the expressions needed for prediction of the multiples, following the ideas of Morley, in a form that can be used to estimate the reflectivity of a water bottom that has a complex shape and has a reflectivity that varies with lateral position, frequency, and reflection angle. The specific form of the operations needed for prediction is implemented without assumptions about the simplicity or flatness of the water bottom. The derivation implies that the recorded wave field may be interpreted as both an upgoing and a downgoing wave. This interpretation is correct except for a simple surface ghost present in both interpretations. Application of the predictive method to data collected over a hard, complex water bottom demonstrates that it effectively attenuates water‐bottom and peg‐leg multiples even when the water bottom is complex and changes in character within the span of a shot gather. The same data were processed with various combinations of predictive attenuation, prestack automatic gain control, prestack moveout discrimination, and stacking. The multiple attenuation achieved with the predictive method alone was greater than that achieved by moveout discrimination alone; the net attenuation achieved by sequential application of all the methods was approximately additive.

Multiple attenuation: some current techniques

1989 ◽  
Vol 20 (2) ◽  
pp. 275 ◽  
Author(s):  
J. Wardell ◽  
P. Whiting
Keyword(s):  
Water Layer ◽  
Velocity Difference ◽  
Periodic Sequences ◽  
Multiple Attenuation ◽  
Predictive Deconvolution ◽  
Recent Approach ◽  
Short Period ◽  
Recorded Data ◽  
P Domain ◽  
Recent Variation

Multiple attenuation techniques have to be based on some difference between the multiples and the primary reflections. The two major differences that are exploited are firstly velocity, and secondly the fact that multiples are periodic sequences of events, and hence are predictable, while the primaries are non-periodic. The widely used frequency-wavenumber (F-K) domain techniques rely on velocity difference only, but a recent variation of this method also makes use of any difference in dip between primaries and multiples to give significantly greater multiple attenuation. For short period multiples, velocity differences may be insufficient for much attenuation, and the process has to be based on the multiple's periodicity, using some type of long predictive deconvolution operator. One problem with this approach is that the multiple period varies with time, particularly at long offsets. Transforming the record to the tau-p domain removes this variation however, allowing more effective deconvolution of the multiples. Another recent approach is to model a multiples-only record by wave equation methods, and subtract it from the recorded data. At present however, this is limited to well defined multiple generators, such as the water layer. With the variety of multiple attenuation processes available today, the geophysicist needs to understand the types of multiple problem to which each is most suited, in order to select the technique most applicable to his data.

Demultiple strategies in the submarine slope of Taiwan accretionary wedge

2020 ◽  
Author(s):  
Feisal Dirgantara ◽  
Andrew Tien-Shun Lin ◽  
Char-Shine Liu ◽  
Song-Chuen Chen
Keyword(s):  
Shallow Water ◽  
Seismic Data ◽  
Sampling Rate ◽  
Water Layer ◽  
Noise Removal ◽  
Accretionary Wedge ◽  
Reflection Seismic ◽  
Multiple Attenuation ◽  
Predictive Deconvolution ◽  
Short Period

<p>Reducing multiple contaminations in reflection seismic data remains one of the greatest challenges in seismic processing and its effectiveness is highly dependent on geologic settings. We undertook two-dimensional reflection seismic data crossing the upper and lower accretionary wedge slopes off SW Taiwan to test the efficiency of various multiple-attenuation scenarios. The area has resulted from an incipient arc-continent collision between the northern rifted margin of the South China Sea and the Luzon volcanic arcs. The wedge extends from shallow water to deep water bathymetries, hence promoting both short-period and long-period multiples within the seismic records. The multichannel seismic data were achieved under 468 hydrophones, 4-ms sampling rate, 12.5-m channel spacing, 50-m shot spacing and 15-second recording length. Preprocessing flow includes swell noise removal, direct wave mute, and missing channel and shot restoration. A subset of demultiple methods based on the periodicity nature and the spatial move-out behavior of multiples were explored to attenuate multiples energy under different geologic environments. The first step relies on the simultaneous subtraction of surface-related multiples, which combined wave-equation multiple attenuation (WEMA) and surface-related multiple elimination (SRME). WEMA is a shot domain multiple attenuations based on a combination of numerical wave extrapolation through the water layer and the water bottom reflectivity. This method was capable to partially suppress the water layer multiples. SRME was applied to attenuate the residual multiple energy at near-offset. This method assumes surface-related multiples can be kinematically predicted by convolution of prestack seismic traces at possible surface multiple reflection locations. Some primary reflections seem to be better retained after the combined subtraction process than using WEMA or SRME filtering independently. The second step lies on parabolic Radon transform to attenuate far-offset multiples by subtracting the noise energy in <em>tau-p</em> on input gathers that have been corrected for normal move-out and inverse transform the remaining primary energy back to CMP-offset domain. Predictive deconvolution in the <em>x-t</em> domain was performed to attenuate low-frequency reverberations in the upper wedge slope. A double-gap deconvolution operator was extended to predict reverberations with correct relative amplitudes, followed by time-variant bandpass filtering to reduce much of residual multiple energy. In general, WEMA and predictive deconvolution were more effective in attenuating the multiples energy at the upper wedge slope where the water depths are shallower; whereas SRME and parabolic Radon were capable of reducing the energy of multiples at the lower wedge slope. Nevertheless, multiples energy could not be fully eliminated due to several factors. The dependency of some demultiple methods (e.g. parabolic Radon, WEMA, SRME) on velocity function may perturb the forward multiple predictions before subtraction as primary velocities might not be present due to the highly tilted strata in the thrust belts domain. Furthermore, parabolic Radon may not perform well in shallow water and area with slowly increasing velocities with depth (e.g. the upper wedge slope). Since the reflection seismic dataset spans various tectonic environments and water depth, results suggest there was no single demultiple method capable to suppress multiples in all environments.</p>

Optical diagnostics of convective structures induced by non-stationary boundary conditions in a vertical water layer

2018 ◽  
Vol 10 (4) ◽  
pp. 134-144 ◽  
Author(s):  
Yu.N. Dubnishchev ◽  
V.A. Arbuzov ◽  
E.V. Arbuzov ◽  
V.S. Berdnikov ◽  
S.A. Kislytsin ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Optical Diagnostics ◽  
Water Layer ◽  
Stationary Boundary ◽  
Convective Structures
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