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.

scholarly journals PENERAPAN METODE F-K DEMULTIPLE DALAM KASUS ATENUASI WATER-BOTTOM MULTIPLE

2016 ◽  
Vol 11 (1) ◽  
pp. 33
Author(s):  
Subarsyah Subarsyah ◽  
Sahudin Sahudin
Keyword(s):  
Seismic Data ◽  
Final Section ◽  
Signal To Noise Ratio ◽  
Multiple Reflections ◽  
Seismic Section ◽  
Multiple Attenuation ◽  
Seismic Acquisition ◽  
Marine Seismic ◽  
Second Category ◽  
Water Bottom

Keberadaan water-bottom multiple merupakan hal yang tidak bisa dihindari dalam akuisisi data seismik laut, tentu saja hal ini akan menurunkan tingkat perbandingan sinyal dan noise. Beberapa metode atenuasi telah dikembangkan dalam menekan noise ini. Metode atenuasi multiple diklasifikasikan dalam tiga kelompok meliputi metode dekonvolusi yang mengidentifikasi multiple berdasarkan periodisitasnya, metode filtering yang memisahkan refleksi primer dan multiple dalam domain tertentu (F-K,Tau-P dan Radon domain) serta metode prediksi medan gelombang. Penerapan metode F-K demultiple yang masuk kategori kedua akan diterapkan terhadap data seismik PPPGL tahun 2010 di perairan Teluk Tomini. Atenuasi terhadap water-bottom multiple berhasil dilakukan akan tetapi pada beberapa bagian multiple masih terlihat dengan amplitude relatif lebih kecil. F-K demultiple tidak efektif dalam mereduksi multiple pada offset yang pendek dan multiple pada zona ini yang memberikan kontribusi terhadap keberadaan multiple pada penampang akhir. Kata kunci : F-K demultiple, multiple, atenuasi The presence of water-bottom multiple is unavoidable in marine seismic acquisition, of course, this will reduce signal to noise ratio. Several attenuation methods have been developed to suppress this noise. Multiple attenuation methods are classified into three groups first deconvolution method based on periodicity, second filtering method that separates the primary and multiple reflections in certain domains (FK, Tau-P and the Radon domain) ang the third method based on wavefield prediction. Application of F-K demultiple incoming second category will be applied to the seismic data in 2010 PPPGL at Tomini Gulf waters. Attenuation of the water-bottom multiple successful in reduce multiple but in some parts of seismic section multiple still visible with relatively smaller amplitude. FK demultiple not effective in reducing multiple at near offset and multiple in this zone contribute to the existence of multiple in final section. Key words : F-K demultiple, multiple, attenuation

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.

SOME CHARACTERISTICS OF MARINE SPARKER SEISMIC DATA

Geophysics ◽  
1972 ◽  
Vol 37 (3) ◽  
pp. 462-470 ◽  
Author(s):  
F. T. Allen
Keyword(s):  
Seismic Data ◽  
Water Layer ◽  
Seismic Survey ◽  
Multiple Reflections ◽  
Time Profiles ◽  
Survey Technique ◽  
Recording Conditions ◽  
Single Detector ◽  
Marine Seismic ◽  
The Relationship

The marine seismic survey technique of frequent recordings with a single detector group can provide intricate details valuable to relatively shallow investigations. Velocities may be computed from time anomalies, under certain circumstances. The extent of multiple energy response is an indication that the 100,000-joule source is strong enough for the purpose. Recognizable minor details in primary reflections are important clues in identifying related multiple reflections. Bounces off the underside of the water layer are rarely found. The pattern and character of reflections are influenced by recording conditions; thus, the relationship between recorded events and sedimentary beds is not simple. Seismic time profiles frequently give wrong impressions of structural attitudes because of the horizontal‐to‐vertical exaggeration, time anomalies, and multiple reflections, as well as the usual effects of velocity differences. The interpreted cross‐section gives a reasonably correct (even if velocities are assumed) impression of structure; the profile often does not.

scholarly journals Measuring Current in a Power Converter Using Fuzzy Automatic Gain Control

2021 ◽  
Vol 11 (13) ◽  
pp. 5793
Author(s):  
Bartosz Dominikowski
Keyword(s):  
High Resolution ◽  
Fuzzy Controller ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Measurement Range ◽  
Power Converter ◽  
Current Measurement ◽  
Dc Power ◽  
Programmable Gain ◽  
Electric Loads

The accuracy of current measurements can be increased by appropriate amplification of the signal to within the measurement range. Accurate current measurement is important for energy monitoring and in power converter control systems. Resistance and inductive current transducers are used to measure the major current in AC/DC power converters. The output value of the current transducer depends on the load motor, and changes across the whole measurement range. Modern current measurement circuits are equipped with operational amplifiers with constant or programmable gain. These circuits are not able to measure small input currents with high resolution. This article proposes a precise loop gain system that can be implemented with various algorithms. Computer analysis of various automatic gain control (AGC) systems proved the effectiveness of the Mamdani controller, which was implemented in an MCU (microprocessor). The proposed fuzzy controller continuously determines the value of the conversion factor. The system also enables high resolution measurements of the current emitted from small electric loads (≥1 A) when the electric motor is stationary.

Coherent noise in marine seismic data

Geophysics ◽  
1983 ◽  
Vol 48 (7) ◽  
pp. 854-886 ◽  
Author(s):  
Ken Larner ◽  
Ron Chambers ◽  
Mai Yang ◽  
Walt Lynn ◽  
Willon Wai
Keyword(s):  
Seismic Data ◽  
Noise Suppression ◽  
Seismic Source ◽  
Coherent Noise ◽  
Critical Data ◽  
Predictive Deconvolution ◽  
Scattered Energy ◽  
Marine Seismic ◽  
The Many ◽  
Water Bottom

Despite significant advances in marine streamer design, seismic data are often plagued by coherent noise having approximately linear moveout across stacked sections. With an understanding of the characteristics that distinguish such noise from signal, we can decide which noise‐suppression techniques to use and at what stages to apply them in acquisition and processing. Three general mechanisms that might produce such noise patterns on stacked sections are examined: direct and trapped waves that propagate outward from the seismic source, cable motion caused by the tugging action of the boat and tail buoy, and scattered energy from irregularities in the water bottom and sub‐bottom. Depending upon the mechanism, entirely different noise patterns can be observed on shot profiles and common‐midpoint (CMP) gathers; these patterns can be diagnostic of the dominant mechanism in a given set of data. Field data from Canada and Alaska suggest that the dominant noise is from waves scattered within the shallow sub‐buttom. This type of noise, while not obvious on the shot records, is actually enhanced by CMP stacking. Moreover, this noise is not confined to marine data; it can be as strong as surface wave noise on stacked land seismic data as well. Of the many processing tools available, moveout filtering is best for suppressing the noise while preserving signal. Since the scattered noise does not exhibit a linear moveout pattern on CMP‐sorted gathers, moveout filtering must be applied either to traces within shot records and common‐receiver gathers or to stacked traces. Our data example demonstrates that although it is more costly, moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data‐dependent processing steps of predictive deconvolution and velocity analysis.

Dual cavity optical automatic gain control for EDFAs

2003 ◽  
Author(s):  
M.F. Krol ◽  
Yongqian Liu ◽  
J.J. Watkins ◽  
D.W. Lambert
Keyword(s):  
Automatic Gain Control ◽  
Gain Control
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