scholarly journals An optimised one-way wave migration method for complex media with arbitrarily varying velocity based on eigen-decomposition

2021 ◽  
Vol 18 (5) ◽  
pp. 776-787
Author(s):  
Anyu Li ◽  
Xuewei Liu
Keyword(s):  
Small Scale ◽  
Complex Media ◽  
Helmholtz Operator ◽  
Depth Migration ◽  
New Strategy ◽  
Infinite Norm ◽  
Eigen Decomposition ◽  
Wave Migration ◽  
Imaging Performance ◽  
Eigenvalue And Eigenvector

Abstract The classical one-way generalised screen propagator (GSP) and Fourier finite-difference (FFD) schemes have limitations in imaging large angles in complex media with substantial lateral variations in wave velocity. Some improvements to the classical one-way wave scheme have been proposed with optimised methods. However, the performance of these methods in imaging complex media remains unsatisfying. To overcome this issue, a new strategy for wavefield extrapolation based on the eigenvalue and eigenvector decomposition of the Helmholtz operator is presented herein. In this method, the square root operator is calculated after the decomposition of the Helmholtz operator at the product of the eigenvalues and eigenvectors. Then, Euler transformation is applied using the best polynomial approximation of the trigonometric function based on the infinite norm, and the propagator for one-way wave migration is calculated. According to this scheme, a one-way operator can be computed more accurately with a lower-order expansion. The imaging performance of this scheme was compared with that of the classical GSP, FFD and the recently developed full-wave-equation depth migration (FWDM) schemes. The impulse responses in media with arbitrary velocity inhomogeneity demonstrate that the proposed migration scheme performs better at large angles than the classical GSP scheme. The wavefronts calculated in the dipping and salt dome models illustrate that this scheme can provide a precise wavefield calculation. The applications of the Marmousi model further demonstrate that the proposed approach can achieve better-migrated results in imaging small-scale and complex structures, especially in media with steep-dipping faults.

2D anisotropic multicomponent Gaussian-beam migration under complex surface conditions

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. S89-S102 ◽  
Author(s):  
Jianguang Han ◽  
Qingtian Lü ◽  
Bingluo Gu ◽  
Jiayong Yan ◽  
Hao Zhang
Keyword(s):  
Gaussian Beam ◽  
Complex Surface ◽  
Dynamic Features ◽  
Surface Conditions ◽  
Depth Migration ◽  
Surface Areas ◽  
Local Plane ◽  
Gaussian Beam Migration ◽  
Wave Migration ◽  
Irregular Topography

Elastic-wave migration in anisotropic media is a vital challenge, particularly for areas with irregular topography. Gaussian-beam migration (GBM) is an accurate and flexible depth migration technique, which is adaptable for imaging complex surface areas. It retains the dynamic features of the wavefield and overcomes the multivalued traveltimes and caustic problems of Kirchhoff migration. We have extended the GBM method to work for 2D anisotropic multicomponent migration under complex surface conditions. We use Gaussian beams to calculate the wavefield from irregular topography, and we use two schemes to derive the down-continued recorded wavefields. One is based on the local slant stack as in classic GBM, in which the PP- and PS-wave seismic records within the local region are directly decomposed into local plane-wave components from irregular topography. The other scheme does not perform the local slant stack. The Green’s function is calculated with a Gaussian beam summation emitted from the receiver point at the irregular surface. Using the crosscorrelation imaging condition and combining with the 2D anisotropic ray-tracing algorithm, we develop two 2D anisotropic multicomponent Gaussian-beam prestack depth migration (GB-PSDM) methods, i.e., using the slant stack and nonslant stack, for irregular topography. Numerical tests demonstrate that our anisotropic multicomponent GB-PSDM can accurately image subsurface structures under complex topography conditions.

scholarly journals A New Strategy for Utilizing Rice Forage Production Using a No-Tillage System to Enhance the Self-Sufficient Feed Ratio of Small Scale Dairy Farming in Japan

2014 ◽  
Vol 6 (8) ◽  
pp. 4975-4989 ◽  
Author(s):  
Windi Zahra ◽  
Takeshi Yasue ◽  
Naomi Asagi ◽  
Yuji Miyaguchi ◽  
Bagus Purwanto ◽  
...  
Keyword(s):  
Dairy Farming ◽  
The Self ◽  
Feed Ratio ◽  
Small Scale ◽  
No Tillage ◽  
Forage Production ◽  
New Strategy ◽  
Tillage System ◽  
Small Scale Dairy

scholarly journals Attenuating multiple-related imaging artifacts using combined imaging conditions

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. S469-S475 ◽  
Author(s):  
Carlos Alberto da Costa Filho ◽  
Andrew Curtis
Keyword(s):  
Small Scale ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Depth Migration ◽  
Time Migration ◽  
Migration Method ◽  
Combined Imaging ◽  
Spatial Locations ◽  
Imaging Conditions

The objective of prestack depth migration is to position reflectors at their correct subsurface locations. However, migration methods often also generate artifacts along with physical reflectors, which hamper interpretation. These spurious reflectors often appear at different spatial locations in the image depending on which migration method is used. Therefore, we have devised a postimaging filter that combines two imaging conditions to preserve their similarities and to attenuate their differences. The imaging filter is based on combining the two constituent images and their envelopes that were obtained from the complex vertical traces of the images. We have used the method to combine two images resulting from different migration schemes, which produce dissimilar artifacts: a conventional migration method (equivalent to reverse time migration) and a deconvolution-based imaging method. We show how this combination may be exploited to attenuate migration artifacts in a final image. A synthetic model containing a syncline and stochastically generated small-scale heterogeneities in the velocity and density distributions was used for the numerical example. We compared the images in detail at two locations where spurious events arose and also at a true reflector. We found that the combined imaging condition has significantly fewer artifacts than either constituent image individually.

Quantitative common angle depth migration: A tool for AVA analysis in complex media

2003 ◽  
Author(s):  
M. Beele ◽  
R. M. Baina ◽  
B. Duquet ◽  
H. Calandra
Keyword(s):  
Complex Media ◽  
Depth Migration

Plane-wave depth migration

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. S261-S272 ◽  
Author(s):  
Paul L. Stoffa ◽  
Mrinal K. Sen ◽  
Roustam K. Seifoullaev ◽  
Reynam C. Pestana ◽  
Jacob T. Fokkema
Keyword(s):  
Phase Space ◽  
Plane Wave ◽  
Plane Waves ◽  
Computation Time ◽  
Depth Migration ◽  
Velocity Modeling ◽  
Natural Domain ◽  
Data Volume ◽  
Wave Migration ◽  
Slant Stacking

We present fast and efficient plane-wave migration methods for densely sampled seismic data in both the source and receiver domains. The methods are based on slant stacking over both shot and receiver positions (or offsets) for all the recorded data. If the data-acquisition geometry permits, both inline and crossline source and receiver positions can be incorporated into a multidimensional phase-velocity space, which is regular even for randomly positioned input data. By noting the maximum time dips present in the shot and receiver gathers and constant-offset sections, the number of plane waves required can be estimated, and this generally results in a reduction of the data volume used for migration. The required traveltime computations for depth imaging are independent for each particular plane-wave component. It thus can be used for either the source or the receiver plane waves during extrapolation in phase space, reducing considerably the computational burden. Since only vertical delay times are required, many traveltime techniques can be employed, and the problems with multipathing and first arrivals are either reduced or eliminated. Further, the plane-wave integrals can be pruned to concentrate the image on selected targets. In this way, the computation time can be further reduced, and the technique lends itself naturally to a velocity-modeling scheme where, for example, horizontal and then steeply dipping events are gradually introduced into the velocity analysis. The migration method also lends itself to imaging in anisotropic media because phase space is the natural domain for such an analysis.

scholarly journals Maritime Security Governance: A New Strategy Management To Avoid Piracy In The Gog And Its Legal Guarantee

2021 ◽  
Vol 8 (10) ◽  
pp. 405-437
Author(s):  
Debi Broohm
Keyword(s):  
Strategy Management ◽  
Mitigation Strategies ◽  
Small Scale ◽  
Gulf Of Guinea ◽  
Maritime Piracy ◽  
Security Governance ◽  
Protect Area ◽  
New Strategy ◽  
Late 21St Century ◽  
Illegal Activities

In the late 21st century, the growth of sea ships widened the horizons for trade on a global level. However, despite slow and cumulatively significant developments in transportation technology, during the era of sail, high sea maritime instability or the threats of piracy remained a significant obstacle to trade over long distances. In addition, with limited solidarity among all essential players in the region, several Gulf of Guinea (GoG) states can diversify their national attention to handle the pandemic instead of combating illegal activities at sea. Therefore, this article talks about the different factors of maritime piracy in the GoG, Comparing the trend across the region's different states (Togo, Benin, Nigeria, Ghana), the current maritime insecurity mitigation strategies proposed, and their gaps. Besides, a discussion around a knowledge gap in terms of accurate cooperation via the various policies implemented by those institutions brings us to propose coevolution governance in the shadow of the hierarchy and to create a maritime protect area (MPA) in the GoG country who do not have it yet, especially in Togo, Ghana, and Nigeria, and surround MPA with sustainably managed fishing areas where local small-scale fishers enjoy exclusive rights. The result shows that regionally it can help Centralize and diffuse the best practices, develop greater synergy among public policies and institutions, and nationally create greater sustainability of conservation with the integration of socio-economic concern and harmonization of strategic planning, practices, and policies.

scholarly journals Using Micro Management Techniques to Overcome Problems in Group Assignments

10.28945/2710 ◽  
2003 ◽  
Author(s):  
Marilyn Ford ◽  
Jenny Morice
Keyword(s):  
Information Technology ◽  
Technology Education ◽  
Team Work ◽  
Small Scale ◽  
Information Technology Education ◽  
Three Phase ◽  
New Strategy ◽  
Management Techniques

Group assignments are becoming increasingly popular in education, including Information Technology education. This paper explores problems with the use of group assignments and offers a new strategy designed to keep the good features of group assignments while removing the negative. Many students in Information Technology believe they should have group assignments because they will be working in groups in industry. Staff sometimes justify the use of group assignments as preparing students for team work in industry. However, we suggest that many problems with group assignments can be overcome by making group assignments more closely replicate conditions in industry. We propose a three-phase strategy using management techniques on a small scale.

scholarly journals Communicating and Visualising Urban Planning in Cold War Berlin

2020 ◽  
Vol 5 (2) ◽  
pp. 10-23 ◽  
Author(s):  
Christoph Bernhardt ◽  
Kathrin Meissner
Keyword(s):  
Urban Planning ◽  
Urban Renewal ◽  
Large Scale ◽  
West Germany ◽  
Small Scale ◽  
Media Campaigns ◽  
East And West Germany ◽  
New Strategy ◽  
East And West ◽  
Post War

This article analyses the dynamics of communication, specifically with regard to the significance of visualisations in urban planning between the two competing political regimes of East and West Germany in divided Berlin (1945–1989). The article will demonstrate the ways in which planners on either side of the Iron Curtain were confronted with matters unique to their own political contexts and conditions for public communication, as well as how they faced similar challenges in fields of urban renewal and negotiating public participation. The post-war decades in Berlin were marked by strong planning dynamics: large-scale reconstruction after WWII and the ‘showcase character’ of political confrontation and competition. In this context, new strategies of communicating urban planning to the public were developed, such as large-scale development plans, public exhibitions and cross-border media campaigns. Paradigmatic shifts during the mid-1970s generated new discourses about urban renewal and historic preservation. The new focus on small-scale planning in vivid and inhabited inner-city neighbourhoods made new forms of communication and public depiction necessary. In the context of social and political change as well as growing mediatisation, planning authorities utilised aspects of urban identity and civic participation to legitimise planning activities. The article traces two small-scale planning projects for neighbourhoods in East and West Berlin and investigates the interrelation of visual communication instruments in public discourses and planning procedures during the 1980s, a period that prominently featured the new strategy of comprehensive planning. Furthermore, the article highlights the key role of micro-scale changes in the management of urban renewal along both sides of the wall and the emergence of neighbourhood civil engagement and participation.

scholarly journals Physical Model for Small Scale Sandwaves Migration in the North Gulf of South China Sea

2009 ◽  
Author(s):  
Mian Lin ◽  
Yong Li ◽  
Wenbin Jiang
Keyword(s):  
South China Sea ◽  
South China ◽  
Physical Models ◽  
Sand Wave ◽  
Small Scale ◽  
Sand Ridge ◽  
Environmental Characteristic ◽  
China Sea ◽  
The North ◽  
Wave Migration

The aim of this paper is to investigate the mechanism of small scale sand-wave migration. According to the environmental characteristic of the north gulf of South China Sea, a quasi-3D mechanics model has been built for simulating the small scale sand wave migration. The calculation results are shown to be consistent with the observed data in the trough of sand ridge. Considering the effect of environmental actions and sand wave features, we develop an effective formula to predict sand-wave migration. It is indicated that the physical models should be used to predict the migration of the small scale sand-wave, which is rarely dominated by wave activity.

An integrated approach for seismic prestack depth migration in complex media

1995 ◽  
Author(s):  
Fu‐gui Liu ◽  
Chuan‐bo Leng ◽  
Chang‐chun Yang ◽  
You‐ming Li
Keyword(s):  
Integrated Approach ◽  
Complex Media ◽  
Prestack Depth Migration ◽  
Depth Migration
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