[발표] 2015개정 실과 교육과정 ‘가정생활’ 영역 개발 방향

We derive an expression for the error introduced by the second-order accurate temporal finitedifference (FD) operator, as present in the FD, pseudospectral and spectral element methods for seismic wave modeling applied to time-invariant media. The 'time-dispersion' error speeds up the signal as a function of frequency and time step only. Time dispersion is thus independent of the propagation path, medium or spatial modeling error.We derive two transforms to either add or remove time dispersion from synthetic seismograms after a simulation. The transforms are compared to previous related work and demonstrated on wave modeling in acoustic as well as elastic media. In addition, an application to imaging is shown. The transforms enable accurate computation of synthetic seismograms at reduced cost, benefitting modeling applications in both exploration and global seismology. The Author(s) 2017. Published by Oxford University Press. All rights reserved. (Less)

/pdf/eliminating-time-dispersion-from-seismic-wave-modeling-25ur888fk1.pdf

Eliminating time dispersion from seismic wave modeling

Adaptive waveform inversion (AWI) reformulates the misfit function used to perform full-waveform inversion (FWI), so that it no longer contains local minima related to cycle skipping. It do...

Adaptive waveform inversion: Practice

Because of the combination of optimization algorithms and full wave equations, full-waveform inversion (FWI) has become the frontier of the study of seismic exploration and is gradually becoming one of the essential tools for obtaining the Earth interior information. However, the application of conventional FWI to pure reflection data in the absence of a highly accurate starting velocity model is difficult. Compared to other types of seismic waves, reflections carry the information of the deep part of the subsurface. Reflection FWI, therefore, is able to improve the accuracy of imaging the Earth interior further. Here, we demonstrate a means of achieving this successfully by interleaving least-squares RTM with a version of reflection FWI in which the tomographic gradient that is required to update the background macro-model is separated from the reflectivity gradient using the Born approximation during forward modeling. This provides a good update to the macro-model. This approach is then followed by conventional FWI to obtain a final high-fidelity high-resolution result from a poor starting model using only reflection data. Further analysis reveals the high-resolution result is achieved due to a deconvolution imaging condition implicitly used by FWI.

/pdf/reflection-full-waveform-inversion-3qmlprkr1d.pdf

Reflection full waveform inversion

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JB015207

Separation of Migration and Tomography Modes of Full-Waveform Inversion in the Plane Wave Domain

Efficient numerical seismic wavefield modelling is a key component of modern seismic imaging techniques, such as reverse-time migration and full-waveform inversion. Finite difference methods are perhaps the most widely used numerical approach for forward modelling, and here we introduce a novel scheme for implementing finite difference by introducing a time-to-space wavelet mapping. Finite difference coefficients are then computed by minimising the difference between the spatial derivatives of the mapped wavelet and the finite difference operator over all propagation angles. Since the coefficients vary adaptively with different velocities and source wavelet bandwidths, the method is capable to maximise the accuracy of the finite difference operator. Numerical examples demonstrate that this method is superior to standard finite difference methods, while comparable to Zhang’s optimised finite difference scheme.

/pdf/adaptive-finite-difference-for-seismic-wavefield-modelling-2c2gh9supu.pdf

Adaptive finite difference for seismic wavefield modelling in acoustic media

One of reverse-time migrations main limitations is that an unscaled adjoint operator is prone to produce images with low resolution, inaccurate amplitudes, and even artifacts. Least-squares reverse-time migration (LSRTM) was subsequently introduced to mitigate this inadequacy via the use of an approximation to an inverse operator. LSRTM suffers from its own limitations, most importantly from poor condition, which often manifests itself as image artifacts. One approach to ameliorate this issue is to constrain the optimization problem by introducing a penalty term to the cost function. Penalizing estimated parameters for sparsity is one such constraint that has been shown to be effective. A drawback of this technique is that it introduces a trade-off between data fitting and image sparsity. Furthermore, if using the Cauchy constraint, an additional trade-off is introduced due to the requirement to estimate a hyper-parameter. We introduce an alternative approach that mitigates these trade-offs by combining a multiplicative cost function with an effective means for determining the Cauchy hyper-parameter. We also introduce a new formulation of the multiplicative cost function that avoids over-penalization by the constraint via the introduction of a relaxation term. Finally, we seek to improve the computational efficiency by introducing a new approach for computing the step length. As such, our method introduces three novel aspects to constrained LSRTM: (i) a relaxed multiplicative cost function, (ii) semi-automatic estimation of the Cauchy hyper-parameter, and (iii) efficient computation of the step length. We discuss the theory and implementation, followed by application to three synthetic datasets and a real ultrasonic dataset. Given the presence of large salt bodies, elasticity, and noise, along with the directivity of piezoelectric ultrasonic transducers, these datasets provide a challenging test of the approach outlined. Results demonstrate that our method is robust in handling the challenges imposed by these scenarios.

Least-squares reverse-time migration with a multiplicative Cauchy constraint

Seismic anisotropy influences both the kinematics and dynamics of seismic waveforms. If anisotropy is not adequately taken into account during full-waveform seismic inversion (FWI), then inadequacies in the anisotropy model are likely to manifest as significant error in the recovered P-wave velocity model. Conventionally, anisotropic FWI uses either a fixed anisotropy model derived from tomography or such, or it uses a local inversion scheme to recover the anisotropy as part of the FWI; both of these methods can be problematic. In this paper, we show that global rather than local FWI can be used to recover the long-wavelength anisotropy model, and that this can then be followed by more-conventional local FWI to recover the detailed model. We demonstrate this approach on a full 3D field dataset, and show that it avoids problems associated to cross-talk that can bedevil local inversion schemes. Although our method provides a global inversion of anisotropy, it is nonetheless affordable and practical for 3D field data.

Global anisotropic 3D FWI

PreviousNext No AccessSecond International Meeting for Applied Geoscience & EnergyFull-elastic AVA extraction using acoustic FWIAuthors: Michael WarnerJohn ArmitageAdrian UmplebyNikhil ShahHenry DebensFabio ManciniMichael WarnerImperial College London and S-Cube LondonSearch for more papers by this author, John ArmitageS-Cube LondonSearch for more papers by this author, Adrian UmplebyS-Cube LondonSearch for more papers by this author, Nikhil ShahS-Cube LondonSearch for more papers by this author, Henry DebensWoodside Energy Ltd.Search for more papers by this author, and Fabio ManciniWoodside Energy Ltd.Search for more papers by this authorhttps://doi.org/10.1190/image2022-3750777.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail AbstractWe demonstrate that accurate amplitude-vs-angle param-eters can be extracted from raw unprocessed seismic data using purely acoustic full-waveform inversion. The result-ant parameters incorporate the full elastic response of the observed data, and it is not necessary to use elastic FWI in order to determine AVA. This approach naturally corrects for a multitude of other amplitude effects including reflector geometry and transmission losses, and it deals correctly with near-critical and post-critical reflections. FWI-based work-flows are consequently simpler than conventional work-flows, and AVA parameters can normally be generated by FWI within days of raw field data first becoming available.Keywords: FWI, AVA, AVO, elastic, acousticPermalink: https://doi.org/10.1190/image2022-3750777.1FiguresReferencesRelatedDetailsCited bySuperior resolution through multiparameter FWI imaging: A new philosophy in seismic processing and imagingJames McLeman, Tom Rayment, Tim Burgess, Karen Dancer, Gary Hampson, and Alex Pauli3 January 2023 | The Leading Edge, Vol. 42, No. 1 Second International Meeting for Applied Geoscience & EnergyISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2022 Pages: 3694 publication data© 2022 Published in electronic format with permission by the Society of Exploration Geophysicists and the American Association of Petroleum GeologistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 15 Aug 2022 CITATION INFORMATION Michael Warner, John Armitage, Adrian Umpleby, Nikhil Shah, Henry Debens, and Fabio Mancini, (2022), "Full-elastic AVA extraction using acoustic FWI," SEG Technical Program Expanded Abstracts : 907-911. https://doi.org/10.1190/image2022-3750777.1 Plain-Language Summary KeywordsFWIAVAAVOelasticacousticPDF DownloadLoading ... 

Full-elastic AVA extraction using acoustic FWI

Summary In this paper we present an integrated concept for seismic acquisition using low powered (Autonomous Underwater Vehicles (AUVs). We show the latest results from its development from the design of the units to their testing. We show how these units perform during flight and their capability to record good-quality seismic data. We then discuss survey design examples to highlight the potential benefits of this system. Using the 2015 Gorgon 3D OBN survey as a case study, we demonstrate that AUVs efficiency is roughly double that of Remotely Operated Vehicles (ROV)-deployed nodes and, since the AUVs can reposition themselves, densifying the node patch does not incur any time penalty once deployed. We also highlight that this approach is efficient for FWI-oriented surveys, either independently or in a hybrid configuration with streamers. 

A New Generation of Autonomous Ocean-Bottom Nodes: Their Development and Applications

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