Image Gathers Research Articles

High-fidelity complete wavefield velocity model building and imaging in shallow water environments – A North Sea case study

Accurate sub-surface image reconstruction from prestack depth migration of surface seismic wavefields requires precise knowledge of the local propagation velocities between the recording location and the image location at depth. Such velocity information has traditionally been derived by tomographically inverting residual moveout information of common image gathers, which have been computed using an initial velocity field. This methodology proves to be challenging in shallow water environments, particularly when strong and rapid velocity variations in the very shallow overburden need to be recovered, while moveout information from reflected arrivals is very sparse or not available.

Borehole seismic quantitative diagnosis of a seismic velocity model for 3D seismic imaging of subsurface structures

ABSTRACTQuantifying uncertainties of surface seismic velocity models is a difficult task. The use of multifarious vertical seismic profiling data provides quantification of velocity model uncertainties. Two borehole seismic diagnosis methods for velocity model uncertainties are developed. The first method is performed with 3D ray‐traced first arrival times through a surface seismic velocity model and compared with measured first arrival times from downhole receivers. It generates a profile of absolute and relative misfits, indicating the velocity uncertainty as a function of depth. The second approach directly compares the differences between the first arrival incident angles measured from 3‐C borehole seismic data and the calculated first arrival incident angles of seismic rays through the velocity model to quantify the model uncertainties. Five seismic velocity models in the Gulf of Mexico are diagnosed using the diagnosis methods with up to six sets of borehole seismic data recorded in three wells. The uncertainty profiles vary with depths and azimuths, revealing the complexity of velocity model uncertainties and providing some clues for further velocity updating. The diagnosis methods are used as velocity updating QC tools and integrated with the conventional seismic velocity updating flow to complement the criteria of flat common image gathers.

How to decide which oblique image has the highest mapping potential for monoplotting method: a case studies on river erosion and floods

Abstract. When studying the development of different geomorphic processes, floods, glaciers or even cultural heritage through time, one cannot rely only on regular photogrammetrical procedures and metrical images. In a majority of cases the only available images are the archive images with unknown parameters of interior orientation showing the object of interest in oblique view. With the help of modern high resolution digital elevation models derived from aerial or terrestrial laser scanning (lidar) or from photogrammetric stereo-images by automatic image-matching techniques even single nonmetric high or low oblique image from the past can be applied in the monoplotting procedure to enable 3D-data extraction of changes through time. The first step of the monoplotting procedure is the orientation of an image in the space by the help of digital elevation model (DEM). When using oblique images tie points between an image and DEM are usually too sparse to enable automatic exterior orientation, still the manual interactive orientation using common features can resolve such shortages. The manual interactive orientation can be very time consuming. Therefore, before the start of the manual interactive orientation one should be certain if one can expect useful results from the chosen image. But how to decide which image has the highest mapping potential before we introduce a certain oblique image in orientation procedure? The test examples presented in this paper enable guidance for the use of monoplotting method for different geoscience applications. The most important factors are the resolution of digital elevation model (the best are the lidar derived ones), the presence of appropriate common features and the incidence angle of the oblique images (low oblique images or almost vertical aerial images are better). First the very oblique example of riverbank erosion on Dragonja river, Slovenija, is presented. Than the test example of September 2010 floods on Ljubljana moor is discussed. Finally, case study from November 2012 floods is presented. During November 2012 floods an initiative was launched to gather as much non-metrical images of floods as possible from casual observers (volunteered image gathering). From all gathered images the guidelines presented before helped to pick out 21% images which were used for monoplotting.

Noise removal by migration of time-shift images

When using seismic data to image complex structures, the reverse time migration (RTM) algorithm generally provides the best results when the velocity model is accurate. With an inexact model, moveouts appear in common image gathers (CIGs), which are either in the surface offset domain or in subsurface angle domain; thus, the stacked image is not well focused. In extended image gathers, the strongest energy of a seismic event may occur at non-zero-lag in time-shift or offset-shift gathers. Based on the operation of RTM images produced by the time-shift imaging condition, the non-zero-lag time-shift images exhibit a spatial shift; we propose an approach to correct them by a second pass of migration similar to zero-offset depth migration; the proposed approach is based on the local poststack depth migration assumption. After the proposed second-pass migration, the time-shift CIGs appear to be flat and can be stacked. The stack enhances the energy of seismic events that are defocused at zero time lag due to the inaccuracy of the model, even though the new focused events stay at the previous positions, which might deviate from the true positions of seismic reflection. With the stack, our proposed approach is also able to attenuate the long-wavelength RTM artifacts. In the case of tilted transverse isotropic migration, we propose a scheme to defocus the coherent noise, such as migration artifacts from residual multiples, by applying the original migration velocity model along the symmetry axis but with different anisotropic parameters in the second pass of migration. We demonstrate that our approach is effective to attenuate the coherent noise at subsalt area with two synthetic data sets and one real data set from the Gulf of Mexico.

Common-reflection-point migration velocity analysis of 2D P-wave data from TTI media

We have developed a common-reflection-point (CRP)-based kinematic migration velocity analysis for 2D P-wave reflection data to estimate the four transversely isotropic (TI) parameters [Formula: see text], [Formula: see text], and [Formula: see text], and the tilt angle [Formula: see text] of the symmetry axis in a TI medium. In each iteration, the tomographic parameter was updated alternately with prestack anisotropic ray-based migration. Iterations initially used layer stripping to reduce the number of degrees of freedom; after convergence was reached, a couple of more iterations over all parameters and all CRPs ensured global interlayer coupling and parameter interaction. The TI symmetry axis orientation was constrained to be locally perpendicular to the reflectors. The [Formula: see text] dominated the inversion, and so it was weighted less than [Formula: see text] and [Formula: see text] in the parameter updates. Estimates of [Formula: see text] and [Formula: see text] were influenced if the error in [Formula: see text] was [Formula: see text]; estimates of [Formula: see text] were also influenced if the error in [Formula: see text] was [Formula: see text]. Examples included data for a simple model with a homogeneous TI layer whose dips allowed recovery of all anisotropy parameters from noise-free data, and a more realistic model (the BP tilted transversely isotropic (TTI) model) for which only [Formula: see text], [Formula: see text], and [Formula: see text] were recoverable. The adequacy of the traveltimes predicted by the inverted anisotropic models was tested by comparing migrated images and common image gathers, with those produced using the known velocity models.

No Fear of Ridicule – Deploying Plaything Technology for Credible Representations of Urban Landscape

As technology affine urban landscape architects, working in Asian mega cities, we conduct research on urbanity beyond prime premises and nice neighbourhoods with maximum tourist potential. We roam through crowded and super narrow, widely informal city layouts, where we apply our digital fieldwork equipment and conduct design work. In these places we test low cost cameras and camera drones, tools that had been developed as documentation equipment for outdoor sportspersons respectively playthings for all the world. Technically limited, if not insufficient and physically labile, these basic tools help us to experiment in the field without problematic loss risks and without scaring people on site. In this paper, we describe a method of on-site data and image gathering, which allows the processing of 3D models of labyrinthine informal city spaces. The result of our study is a three-dimensional puzzle of sufficient precision, making a widely inaccessible and undocumented piece of city terrain visible, understandable and designable.

The Impact of Symbolism on Some British and American Modernist Writers

This paper will be focused on the impact of symbolism on some British and American modernist writers. Through an analysis of the main characteristics of symbolism and modernism, I will arrive to point the level of impact of one literary movement over the other. Symbolism initiated as a drive to portray a different actuality from that of naturalism and realism, producing an impact on modernist literature by moving the focus of narration on word arrangement and images. Being the first symbolist novel, Huysmans’s A Rebour shows artistry in the usage of language. On the other hand, Dujardin’s Les Lauriers sont coupes technique disregarding the cause- effect plot and converging on the gathering of images and symbolic means would be used intensively by Henry James and after WWI writers. The technique of intersecting time, space and disorder of information transmitted through the senses is widely exploited by Mallarme, Rimbaud, Valery and Baudelaire. The impact of Proust on Joyce is touchable not only in the importance given to the connection amid art and life, through the biome of personages and time used in the novel, but also in the significance prearranged by the language to transmit the form of the novel. The personages of Faulkner and Wolf are identified through images, symbols and language used since they subsist only in relation to these symbols and words communication, resulting to be significant forms of modernist technique. What integrates these two literary movements goes further to the usage of joint techniques of expression and is focused on the same ambition of making art, leaving apart affects, taking into consideration its intricacies and impossibilities. DOI: 10.5901/mjss.2014.v5n1p565

Molten Pool Image Processing and Feature Extraction Based on Multiple Visions

A molten pool image gathering system is designed based on multiple visions. By using a composite filter, it can effectively overcome the interference of the welding arc and obtain a clear molten pool image. A series of image processing algorithms has been proposed based on the features of the molten pool image. A median filtering has been used to remove the noise of the molten pool image. A canny multi-threshold method has been used to extract the edge characteristics of the molten pool. Then the edge feature of the molten pool can be gotten after false edge removing and iterative fitting.

Plane-wave least-squares reverse-time migration

A plane-wave least-squares reverse-time migration (LSRTM) is formulated with a new parameterization, where the migration image of each shot gather is updated separately and an ensemble of prestack images is produced along with common image gathers. The merits of plane-wave prestack LSRTM are the following: (1) plane-wave prestack LSRTM can sometimes offer stable convergence even when the migration velocity has bulk errors of up to 5%; (2) to significantly reduce computation cost, linear phase-shift encoding is applied to hundreds of shot gathers to produce dozens of plane waves. Unlike phase-shift encoding with random time shifts applied to each shot gather, plane-wave encoding can be effectively applied to data with a marine streamer geometry. (3) Plane-wave prestack LSRTM can provide higher-quality images than standard reverse-time migration. Numerical tests on the Marmousi2 model and a marine field data set are performed to illustrate the benefits of plane-wave LSRTM. Empirical results show that LSRTM in the plane-wave domain, compared to standard reverse-time migration, produces images efficiently with fewer artifacts and better spatial resolution. Moreover, the prestack image ensemble accommodates more unknowns to makes it more robust than conventional least-squares migration in the presence of migration velocity errors.

Variable-depth streamer acquisition: Broadband data for imaging and inversion

Conventional marine acquisition uses a streamer towed at a constant depth. The resulting receiver ghost notch gives the maximum recoverable frequency. To push this limit, the streamer must be towed at a quite shallow depth, but this compromises the low frequencies. Variable-depth streamer (VDS) acquisition is an acquisition technique aimed at achieving the best possible signal-to-noise ratio at low frequencies by towing the streamer very deeply, but by using a depth profile varying with offset in order not to limit the high-frequency bandwidth by notches as in conventional constant-depth streamer acquisition. The idea is to use notch diversity, each receiver having a different notch, so that the final result, combining different receivers, will have no notches. The key step to process VDS acquisitions is the receiver deghosting. We found that the optimal receiver deghosting, instead of being a preprocessing step, should be done postimaging, by using a dual-input, migration and mirror migration, and a new joint deconvolution algorithm that produces a 3D real amplitude deghosted output. This method can be applied poststack, the inputs being the migration and mirror migration images and the output being the deghosted image. Using a multichannel joint deconvolution, the inputs are the migrated and mirror migrated image gathers and the outputs are the prestack deghosted image gathers. This method preserves the amplitude-versus-offset behavior, as the deghosted output can be seen on synthetic examples to be equal to a reference computed by migrating the data modeled without any reflecting water surface. A real data set was used to illustrate this method, and another one was used to check the possibility of performing prestack elastic inversion on the deghosted gathers.

3D angle gathers with plane-wave reverse-time migration

Angle domain common image gathers (ADCIGs) from reverse-time migration (RTM) provide new tools for imaging complex geologic structures, such as salt flank or subsalt areas, characterized by multiarrivals. Compared with common image gathers from Kirchoff or Beam migration, the ADCIGs from RTM have the advantage of relying on wave propagation, providing a more reliable input for tomography or amplitude analysis. In practice however, most current wide azimuth surveys (e.g., deep-water regions of the Gulf of Mexico) are acquired with coarsely sampled shot and receiver locations on the surface, which leads to severe angular undersampling. This phenomenon is frequently observed on shallow seismic events in high-resolution 3D ADCIGs from common-shot RTM. In addition, because small offsets are frequently not recorded, seismic events are missing at small incidence angles in angle gathers. We have made a detailed study of the angular sampling issue in 3D angle gathers. We then used plane-wave RTM to generate 3D angle gathers. Plane-wave RTM, with its low-cost and automatic angular interpolation, is a promising solution for improving the quality of 3D angle gathers.

Moveout-based wave-equation migration velocity analysis

Current wave-equation migration velocity analysis schemes suffer from problems such as severe nonlinearity (which causes the issue of cycle skipping) and imprecise objective functions (which can accrue velocity errors by honoring residuals caused by model complexity and incomplete acquisition). To provide an improvement, we developed an alternative method to perform wave-equation migration velocity analysis by maximizing the flatness of the angle-domain common image gathers. We replaced the ray-based tomographic operator with the wave-equation-based one, although keeping the conventional moveout-based tomography work flow. Instead of maximizing the image-stack-power objective function directly with respect to the slowness, we linked the objective function to the slowness indirectly through an intermediate moveout parameter. By focusing on the common image gather kinematics, this approach greatly reduced the risk of cycle skipping in the absence of low-frequency data, and it produced high-quality gradients. In addition, the proposed method did not require explicit picking of the moveout parameters. Our numerical examples demonstrated the great potential of this method: in the first example, in which there is a Gaussian-shaped slowness anomaly, our method produced a well-behaved gradient; in the second example, in which there is a horizontally gradual increase of slowness, the result verified that our method is robust against cycle skipping; in the third example, the result showed that our method works well with reflectors of variable dips. Finally, our test on the Marmousi models concluded that the proposed method converges to a high-quality model that uniformly flattens the angle-domain common-image gathers.

One-shot Classification of 2-D Leaf Shapes Using Distributed Hierarchical Graph Neuron (DHGN) Scheme with k-NN Classifier

This article presents a scalable approach for classifying plant leaves using the 2-dimensional shape feature. The proposed approach integrates a distributed recognition scheme called Distributed Hierarchical Graph Neuron (DHGN) for pattern recognition and k-nearest neighbor (k-NN) for pattern classification. With increasing amount of leaves data that can be captured using existing image gathering and processing technology, the ability for any particular classification scheme to produce high recall accuracy while adapting to large-scale dataset and data features is very important. The approach presented in this paper implements a one-shot learning mechanism within a distributed processing infrastructure, enabling large-scale data to be classified efficiently. The experimental results obtained through a series of classification tests indicate that the proposed scheme is able to produce high recall accuracy and large number of perfect recalls for a given plant leaves dataset. Furthermore, the results also indicate that the recognition procedure within the DHGN distributed scheme incurs low computational complexity and minimum processing time.

Optimal stacking for multi-azimuth pre-stack seismic data

SummaryOffshore exploration for hydrocarbons in increasingly challenging environments often requires more advanced acquisition methods than conventional 3D narrowazimuth towed streamer to better image the sub-surface for AVO analysis and reservoir characterization. Multi- Azimuth (MAZ), Wide-Azimuth (WAZ) or Full-Azimuth (FAZ) seismic acquisition overcomes the limitations of the conventional acquisition in better illuminating the sub-surface, suppressing the multiple and enhancing signal to noise (S/N) ratio. Nevertheless, to realize the added value of multi-azimuth data, the data need to be combined in a way that will overcome the issues such as time-shift and amplitude difference due to varied illumination between the surveys.This paper describes a method that can be used for combining MAZ pre-stack data to generate AVOpreserving common image gathers (CIGs) in the presence of poor illumination. Based on the concept of crosscorrelation, MAZ CIGs are first flattened to account for any inaccuracy in the velocity model and imaging process so as to align the events to a pilot. Repeating the crosscorrelation process, weights are then derived from the correlation coefficients and applied to individual offsets that take into account the AVO behaviour. With this post-migration processing, any anomaly in AVO resulted from poor illumination can be mitigated. Applying it on MAZ post-stack data, the method can also provide optimal stacking for obtaining higher S/N images.We demonstrate, through synthetic and real data examples, that clearer images with high AVO fidelity can be obtained from MAZ data using our optimal stacking method.

A robust scheme to output angle-domain common image gathers for shot-profile migration

Angle-domain common image gathers (CIGs) play an important role in migration-based velocity updating. One popular criterion of migration velocity analysis (MVA) is the flatness of common-angle imag...

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• Extracts All Astir P lans are progressing for the Ninth International Melville Society Conference , “Melville and Whitman in Washington: The Civil War Years and After,” to be held in Washington, D. C., from June 4 to June 7, 2013. The George Washington University will be hosting most of the plenary sessions and panels, and cultural events will take place at other venues in the city. The plenary speakers will be John Bryant (Hofstra University), Ed Folsom (University of Iowa), Kenneth M. Price (University of Nebraska, Lincoln), and Elizabeth Renker (Ohio State University). Details about the conference can be found on the Society webpage (melvillesociety.org) under the “Conferences and Events” tab and also on the conference Facebook page, “Melville and Whitman in Washington: The Civil War Years and After.” The Society website has a new look, thanks to its editor Robert Sandberg. It now features three columns, instead of two, in a wider format. When you visit the site, in addition to getting the latest news about upcoming conferences and events, you can read items in two continuously updated newsfeeds from the New Bedford Whaling Museum: one announcing upcoming events and the other displaying the latest contributions to an online Flicker exhibit, “Signifying the Whale.” “Melville’s Marginalia Online,” edited by Steven Olsen-Smith, Peter Norberg, and Dennis C. Marnon, continues to enhance its interface for the photographic display of books scanned or made available by Houghton Library, the Berkshire Athenaeum, Woodstock Theological Center, and the University of Virginia. Villanova University’s Digital Library has assisted the project. Recently mounted volumes include Shakespeare’s Dramatic Works and Sonnets and Wordsworth’s Poetical Works. The interface now includes a filtering option for displaying marked and annotated pages apart from unmarked content. The project invites feedback as well as financial support from users through designated links at http://melvillesmarginalia.org. Scott Norsworthy’s site, “Melvilliana,” which can be found at http://melvilliana.blogspot.com, contains a wealth of information and also links to other Melville-related sites and blogs. John Bryant, director of the Melville Electronic Library (MEL), reports significant progress as MEL completes the first year of its three-year NEH Scholarly Editions grant. Thanks to MEL programmer Nick Laiacona and his staff at Performant Software Solutions, development of TextLab, MEL’s manuscript transcription and print collation tool, is nearing completion. When c 2012 The Melville Society and Wiley Periodicals, Inc. L E V I A T H A N A J O U R N A L O F M E L V I L L E S T U D I E S 77 A L L A S T I R fully operational, TextLab will allow editors to build MEL’s “textual core,” consisting of all versions of Melville’s manuscript and published writings. Thanks also goes to MEL researchers on the TextLab team (Brett Barney, Les Harrison, Wes Raabe, Lewis Ullman, and Marta Werner), who have tested and will continue to test the tool throughout the year. In addition, Bryant and Associate Director Wyn Kelley met at MIT with HyperStudio’s director Kurt Fendt, programmer James Folsom, and associates Ayse Gursoy and Elyse Graham to share news about TextLab and to hear of HyperStudio’s development of Annotation Studio, which will be adapted to MEL as our “Melville Remix” workshop for annotating Melville texts and images. But even as MEL is building these tools (focusing for the time being on Moby-Dick, Battle-Pieces, and Billy Budd), other MEL teams are focusing on building content for annotation. MEL coeditors Dennis Berthold and Bob Wallace are supervising the Moby-Dick and Art project; Kelley and Brian Yothers are building a database of travel-related place names and coordinates for future mappings, and Timothy Marr and Tony McGowan are heading up the Battle-Pieces timeline annotation team. Bryant and Wallace are also supervising the gathering of images of Melville’s print collection from various affiliates: thus far, the Osborne Collection at Southwestern University (TX) and the Melville Society Archive at the New Bedford Whaling Museum have contributed images of over 50 items. Anyone interested in MEL should contact Bryant or Kelley and consider attending MELCamp4, a genial and informative...

Migration from 3D irregular surfaces: A prestack time migration approach

We have developed a modified 3D prestack time migration (PSTM) scheme that can handle rugged topography as well as high near-surface velocities in land seismic imaging. The proposed topography PSTM can be applied to seismic data recorded on a 3D irregular surface without static corrections. Two effective velocity parameters were found to describe wave propagation through inhomogeneous media above and below a chosen datum. As a result, wave propagation phenomena in the complex near surface, such as near-vertical incidences through a weathering layer and raypaths bending away from vertical in the presence of high near-surface velocities, are correctly considered. The two effective velocity parameters can be estimated by flattening events in imaging gathers. Hence, it is not necessary to have detailed knowledge of the near-surface velocity model and velocity field below the datum when applying topography PSTM. We integrated residual static corrections into topography PSTM. This eliminated the distortions along the events better than conventional residual static corrections, which are usually applied before migration. The computational cost of the topography PSTM was only slightly higher than that of conventional PSTM due to the use of a table-driven algorithm. Three-dimensional synthetic and field data sets were used to test the proposed topography PSTM. High-quality imaging results were obtained.

Tomographic velocity inversion for ADCIGs in areas with a rugged surface

Pre-stack depth migration velocity analysis is one of the key techniques influencing image quality. As for areas with a rugged surface and complex subsurface, conventional prestack depth migration velocity analysis corrects the rugged surface to a known datum or designed surface velocity model on which to perform migration and update the velocity. We propose a rugged surface tomographic velocity inversion method based on angle-domain common image gathers by which the velocity field can be updated directly from the rugged surface without static correction for pre-stack data and improve inversion precision and efficiency. First, we introduce a method to acquire angle-domain common image gathers (ADCIGs) in rugged surface areas and then perform rugged surface tomographic velocity inversion. Tests with model and field data prove the method to be correct and effective.

Migration velocity analysis using traveltime wavefield tomography

We introduce an integrated wave-equation technique for migration velocity analysis (MVA) that consists of three steps: (1) forming the extended data, (2) approximating the correct transmitted wavefield, and (3) using wavefield tomography to update the velocity model. In the first step, the crosscorrelation imaging condition is relaxed to produce other nonzero-lag common image gathers (CIG) that, combined, form a common image cube (CIC). Slicing the CIC at different crosscorrelation lags forms a series of CIGs. Flattened events will occur in the CIGs at a lag other than the zero-lag when an incorrect velocity model is used in the migration. In the second step, for each event on the CIG, we pick the focusing depth and crosscorrelation lag at which it is flattest. We then model a Green’s function by seeding a source at the focusing depth using one-way wave equation modeling, then shift the modeled wavefield with the focusing crosscorrelation lag. This process is repeated for the other primary events at different lateral and vertical positions. The result is a set of modeled data whose wavefield approximates the wavefield that would have been generated if the correct velocity model had been used to simulate these gathers. We then apply wavefield tomography on these data-driven modeled data to update the velocity model. Our inversion scheme is based on wave-equation traveltime tomography that can update the velocity model in the presence of large velocity errors and a complex environment. Tests on synthetic and real 2D seismic data confirm the method’s effectiveness in building velocity models in complex structural areas that have large lateral velocity variations.

An angle-domain imaging condition for elastic reverse time migration and its application to angle gather extraction

An angle-domain imaging condition is recommended for multicomponent elastic reverse time migration. The local slant stack method is used to separate source and receiver waves into P- and S-waves and simultaneously decompose them into local plane waves along different propagation directions. We calculated the angle-domain partial images by crosscorrelating every possible combination of the incident and scattered plane P- and S-waves and then organized them into P-P and P-S local image matrices. Local image matrix preserves all the angle information related to the seismic events. Thus, by working in the image matrix, it is convenient to perform different angle-domain operations (e.g., filtering artifacts, correcting polarity, or conducting illumination and acquisition aperture compensations). Because local image matrix is localized in space, these operations can be designed to be highly flexible, e.g., target-oriented, dip-angle-dependent or reflection-angle-dependent. After performing angle-domain operations, we can stack the partial images in the local image matrix to generate the depth image, or partially sum them up to produce different angle-domain common image gathers, which can be used for amplitude versus angle and migration velocity analysis. We tested several numerical examples to demonstrate the applications of this angle-domain image condition.