Migration before stack—Procedure and significance

Geophysics ◽  
1980 ◽  
Vol 45 (2) ◽  
pp. 204-212 ◽  
Author(s):  
Sudhir Jain ◽  
A. Easton Wren
Keyword(s):  
Common Source ◽  
Alternative Technique ◽  
High Frequencies ◽  
Prestack Migration ◽  
Common Depth Point ◽  
Reflection Time ◽  
Time Differential ◽  
Gain Recovery

Common‐depth‐point (CDP) stacking is based on the assumption that reflection points are coincident and situated midway between the respective source and receiver locations. If the reflector is structurally deformed, the reflection points move updip from the midpoint. As the structural dip increases, the reflection points for a CDP group of traces are farther removed from each other and normal stacking procedures [i.e., reflection apparent velocities for horizontal reflectors used for normal moveout (NMO) corrections] become increasingly inaccurate. Under such circumstances prestack migration is desirable, particularly when high frequencies are to be preserved. One published approach to prestack migration (Sattlegger and Stiller, 1973) involves the generation of substacks of adjacent traces followed by migration and summation of individual substacks. While adequate in many instances, cases exist where even substacks are degraded by the reflection time differential between component traces. This paper discusses an alternative technique to prestack migration without recourse to substacks. Common‐source traces, after gain recovery and static time corrections but before NMO corrections, are migrated using Kirchhoff summation. Aperture is computed for each sample according to specified maximum dips. Traces are simultaneously migrated and stacked, then output sequentially in sets of 12. The method is economical and provides enhanced reflection continuity and reliability in comparison to poststack migration. Moreover, the collapsing of diffractions is more effective.

3-D prestack migration in anisotropic media

Geophysics ◽  
1993 ◽  
Vol 58 (1) ◽  
pp. 79-90 ◽  
Author(s):  
Zhengxin Dong ◽  
George A. McMechan
Keyword(s):  
A Priori ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Anisotropic Media ◽  
P Wave ◽  
Common Source ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Prestack Migration ◽  
Time Migration

A three‐dimensional (3-D) prestack reverse‐time migration algorithm for common‐source P‐wave data from anisotropic media is developed and illustrated by application to synthetic data. Both extrapolation of the data and computation of the excitation‐time imaging condition are implemented using a second‐order finite‐ difference solution of the 3-D anisotropic scalar‐wave equation. Poorly focused, distorted images are obtained if data from anisotropic media are migrated using isotropic extrapolation; well focused, clear images are obtained using anisotropic extrapolation. A priori estimation of the 3-D anisotropic velocity distribution is required. Zones of anomalous, directionally dependent reflectivity associated with anisotropic fracture zones are detectable in both the 3-D common‐ source data and the corresponding migrated images.

The impact of bubble curtains on seismic air-gun signatures and its high-frequency emission

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. P1-P11
Author(s):  
Daniel Wehner ◽  
Martin Landrø
Keyword(s):  
High Frequency ◽  
Air Injection ◽  
Offshore Wind ◽  
Peak Amplitude ◽  
Common Source ◽  
High Frequencies ◽  
Air Gun ◽  
Source Signal ◽  
The Impact ◽  
Bubble Curtain

In marine seismic acquisition, air guns are the most common source and, in recent years, research on their impact on the marine environment has increased. The main focus is on the reduction of emitted high frequencies, approximately greater than 200 Hz, which are normally not useful for seismic imaging. Therefore, potential ways to reduce the high frequencies from air guns are investigated and the development of alternative source types has increased. We have investigated the impact of bubble curtains on the source signature from seismic air guns because bubble curtains are known to mitigate high frequencies in other applications, e.g., pile driving for offshore wind farms. We have conducted tank experiments with two different configurations of bubble curtains around a single air gun and compared the results to the conventional source signature without a bubble curtain. The two different bubble curtains vary in size and in the way they are attached to the air gun. The amount of injected air into the bubble curtains is varied for both configurations. We compare the measured results to simulated data using a common model for air-gun source signatures. The results indicate a reduced peak amplitude with increasing air injection through the bubble curtain. This corresponds to a gradually decreasing frequency content for frequencies greater than 50 Hz. The frequencies of the source signal of less than 50 Hz are practically unaffected by the bubble curtain. In addition, the bubble time period of the source signal is slightly increased with an increasing amount of air injection through the bubble curtain. The main cause for the reduced peak amplitude is likely to be a buffer effect of the bubble curtain on the released air. Hence, a bubble curtain concentrated around the air-gun ports could be an efficient and practical solution to reduce the high-frequency acoustic emission from air guns.

True‐amplitude seismic migration: A comparison of three approaches

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 929-936 ◽  
Author(s):  
Samuel H. Gray
Keyword(s):  
Elastic Parameter ◽  
Reflection Point ◽  
Seismic Migration ◽  
Amplitude Variation With Offset ◽  
Prestack Migration ◽  
Fundamental Limitations ◽  
Common Depth Point ◽  
Seismic Records ◽  
Migration Method ◽  
Angle Dependent Reflectivity

Knowledge of elastic parameter (compressional and shear velocities and density) contrasts within the earth can yield knowledge of lithology changes. Elastic parameter contrasts manifest themselves on seismic records as angle‐dependent reflectivity. Interpretation of angle‐dependent reflectivity, or amplitude variation with offset (AVO), on unmigrated records is often hindered by the effects of common‐depth‐point smear, incorrectly specified geometrical spreading loss, source/receiver directivity, as well as other factors. It is possible to correct some of these problems by analyzing common‐reflection‐point gathers after prestack migration, provided that the migration is capable of undoing all the amplitude distortions of wave propagation between the sources and the receivers. A migration method capable of undoing such distortions and thus producing angle‐dependent reflection coefficients at analysis points in a lossless, isotropic, elastic earth is called a “true‐amplitude migration.” The principles of true‐amplitude migration are simple enough to allow several methods to be considered as “true‐amplitude.” I consider three such migration methods in this paper: one associated with Berkhout, Wapenaar, and co‐workers at Delft University; one associated with Bleistein, Cohen, and co‐workers at Colorado School of Mines and, more recently, Hubral and co‐workers at Karlsruhe University; and a third introduced by Tarantola and developed internationally by many workers. These methods differ significantly in their derivations, as well as their implementation and applicability. However, they share some fundamental similarities, including some fundamental limitations. I present and compare summaries of the three methods from a unified perspective. The objective of this comparison is to point out the similarities of these methods, as well as their relative strengths and weaknesses.

scholarly journals Design and simulation of high-swing fully differential telescopic Op-Amp

2021 ◽  
Vol 2 (2) ◽  
pp. 49-57
Author(s):  
Zahra Pezeshki
Keyword(s):  
Power Supply ◽  
Common Source ◽  
High Frequencies ◽  
Fully Differential ◽  
Op Amp ◽  
Op Amps ◽  
Common Gate ◽  
High Cmrr ◽  
The Common ◽  
Very High

This article describes the process of design and simulation of a high-swing fully differential telescopic Operational Amplifier (Op-Amp). Due to the Common Gate-Common Source (CG and CS) cascode structure, the gain is very high. To maximize this gain, the load must also be selected such as two current sources. This circuit has the higher voltage in output than current Op-Amps in accordance with desirable characteristics. The loss of power of this operating amplifier are very low and in milliwatts. With use of a power supply of 1.8 V, it achieves a high-swing 1.2 V, a differential gain of 76.333 dB, ω_uGB of 412 MHz, and 50 dB CMRR. This new design through the simulations and analytically shows that the high-swing fully differential telescopic Op-Amp retains its high CMRR even at high frequencies.

Implicit static corrections in prestack migration of common‐source data

Geophysics ◽  
1990 ◽  
Vol 55 (6) ◽  
pp. 757-760 ◽  
Author(s):  
G. A. McMechan ◽  
H. W. Chen
Keyword(s):  
Surface Velocity ◽  
Common Source ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Near Surface ◽  
Prestack Migration ◽  
Time Migration ◽  
Excitation Time ◽  
Source Data ◽  
Static Corrections

Static effects due to surface topography and near‐surface velocity variations may be accurately compensated for, in an implicit way, during prestack reverse‐time migration of common‐source gathers, obviating the need for explicit static corrections. Receiver statics are incorporated by extrapolating the observed data from the actual recorder positions; source statics are incorporated by computing the excitation‐time imaging conditions from the actual source positions.

Acoustic prestack migration of cross‐hole data

Geophysics ◽  
1988 ◽  
Vol 53 (8) ◽  
pp. 1015-1023 ◽  
Author(s):  
Liang‐Zie Hu ◽  
George A. McMechan ◽  
Jerry M. Harris
Keyword(s):  
Synthetic Data ◽  
Field Application ◽  
Scale Model ◽  
Common Source ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Prestack Migration ◽  
Time Migration ◽  
Time Space ◽  
Low Pass

Subsurface imaging with common‐source cross‐hole data can be achieved using prestack reverse‐time migration. The algorithm consists of extrapolation of the recorded wave field, application of the excitation‐time imaging condition, and postprocessing of the resulting image with a low‐pass wavenumber filter. The wavenumber filter removes the artifact associated with the direct arrival; this artifact is not separable from the scattered data before migration because, in the cross‐hole geometry, they significantly overlap in time, space, and wavenumber. Migration of synthetic data produces the best possible results, but images produced by migration of scale‐model data are not greatly inferior. Apparently, acceptable images can be obtained from a surprisingly few sources, if these sources are located sufficiently far apart to give independent information and the recording aperture is sufficiently wide.

Prestack migration by shot record inversion and common depth point stacking: a case study

First Break ◽  
1989 ◽  
Vol 7 (1221) ◽  
Author(s):  
A. van der Schoot ◽  
R. Romijn ◽  
D.E. Larson ◽  
A.J. Berkhout
Keyword(s):  
Prestack Migration ◽  
Common Depth Point

Quasi-Periodic Oscillations in Dwarf Novae

1979 ◽  
Vol 46 ◽  
pp. 77-88
Author(s):  
Edward L. Robinson
Keyword(s):  
Binary Systems ◽  
Outer Edge ◽  
Light Curves ◽  
Close Binary ◽  
Bright Spot ◽  
Dwarf Novae ◽  
Periodic Oscillations ◽  
High Frequencies ◽  
Short Period ◽  
Typical Time

Three distinct kinds of rapid variations have been detected in the light curves of dwarf novae: rapid flickering, short period coherent oscillations, and quasi-periodic oscillations. The rapid flickering is seen in the light curves of most, if not all, dwarf novae, and is especially apparent during minimum light between eruptions. The flickering has a typical time scale of a few minutes or less and a typical amplitude of about .1 mag. The flickering is completely random and unpredictable; the power spectrum of flickering shows only a slow decrease from low to high frequencies. The observations of U Gem by Warner and Nather (1971) showed conclusively that most of the flickering is produced by variations in the luminosity of the bright spot near the outer edge of the accretion disk around the white dwarf in these close binary systems.

Identifying groups of airborne particles by ordination

1994 ◽  
Vol 52 ◽  
pp. 856-857
Author(s):  
M. Shlepr ◽  
C. M. Vicroy
Keyword(s):  
Elemental Analysis ◽  
Energy Dispersive Spectroscopy ◽  
Manufacturing Process ◽  
Spatial Representation ◽  
Airborne Particles ◽  
Common Source ◽  
Data Set ◽  
Microelectronics Industry ◽  
Induced Changes ◽  
Source Materials

The microelectronics industry is heavily tasked with minimizing contaminates at all steps of the manufacturing process. Particles are generated by physical and/or chemical fragmentation from a mothersource. The tools and macrovolumes of chemicals used for processing, the environment surrounding the process, and the circuits themselves are all potential particle sources. A first step in eliminating these contaminants is to identify their source. Elemental analysis of the particles often proves useful toward this goal, and energy dispersive spectroscopy (EDS) is a commonly used technique. However, the large variety of source materials and process induced changes in the particles often make it difficult to discern if the particles are from a common source.Ordination is commonly used in ecology to understand community relationships. This technique usespair-wise measures of similarity. Separation of the data set is based on discrimination functions. Theend product is a spatial representation of the data with the distance between points equaling the degree of dissimilarity.

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