Amélia Novais

Universidade Estadual de Campinas, Matemática Aplicada, Faculty Member

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Papers by Amélia Novais

How long would it take to try all the antiepileptic drugs available?

Epilepsy Research, 2019

How long would it take to try all the antiepileptic drugs available? AED: antiepileptic drug.

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2.5D Finite-Difference Solution of the Acoustic Wave Equation

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On the estimation of local slopes

Geophysics, Jul 1, 2009

Current algorithms for the estimation of Common Reflection Surface (CRS) parameters are based on ... more Current algorithms for the estimation of Common Reflection Surface (CRS) parameters are based on one-or multi-parameter coherency analysis (semblance) schemes applied to the data. Such procedures, besides computationally expensive, leads to significant uncertainties on the searched parameters. Conventional semblance methods can be avoided for a number imaging tasks if local slopes can be directly extracted from prestack data, for example, by filtering schemes. Although the idea is not at all new, recent literature shows its revival for various purposes, such as velocity analysis, tau-p imaging, migration to zero offset and time migration. Here, we discuss several different ways of extracting the desired slope information from the data. We propose a simple, straightforward correction to linear plane-wave destructors. The correction is based on the observation that additionally to the local slope, also its inverse can be extracted from the data in a fully analogous way. Combining the information of both extractions yields a simple but powerful correction to the local slopes. In our numerical examples, the naive application of simple linear plane-wave destructors with our simple, straightforward correction produced results of high quality, even in an example with a rather high noise level and interfering events.

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A unified Bom- Kirchhoff representation for acoustic media

For the modeling of a single target reflector in a smooth inhomogeneous elastic anisotropic media... more For the modeling of a single target reflector in a smooth inhomogeneous elastic anisotropic media, it has been recently shown that the volume Born integral can be transformed into a surface scattering integral on the reflector. This surface integral has been called Born-Kirchhoff as it relates very naturally to the Kirchhoff-Helmholtz integral, thus providing the theoretical link between the two approaches. Here we specialize the derivation and main properties of the Born-Kirchhoff integral in the acoustic case, and use a simple synthetic example to provide a comparison between the new integral and its classical counterparts.

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Curvelet Denoising for Preconditioning of 2D Poststack Seismic Data Inversion: Application to Data from the Marimbá Oil Field, Offshore Brazil

Pure and Applied Geophysics, May 30, 2023

3D Complex Padé FFD migration: A comparison of splitting techniques

12th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 15–18 August 2011, Mar 13, 2011

Three-dimensional wa ve-equation migration techniques are quite expensive because of the huge mat... more Three-dimensional wa ve-equation migration techniques are quite expensive because of the huge matrices that need to be inverted. Many techniques have been proposed to reduce this cost by splitting the 3D problem into a sequence of 2D problems. We compare the performance of splitting techniques for stable 3D Fourier Finite-Difference (FFD) migration techniques in terms of image quality and computational cost. The FFD methods are complex Pad´ e FFD and FFD plus interpolation, and the compared splitting techniques are two and four-way splitting as well as alternating four-way splitting, i.e., splitting into the coordinate directions at one depth and the diagonal directions at the next level. From numerical examples in homogeneous and inhomogeneous media, we conclude that alternate four-way splitting yields results of the same quality as full four-way splitting at the cost of two-way splitting.

Including lateral velocity variations into true-amplitude wave-equation migration

11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009, Apr 28, 2009

In heterogeneous media, standard one-wave wave equations only describe the kinematic parts of one... more

Estudo de formas implementacionais da equação da onda imagem para remigração na profundidade

10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, Nov 23, 2007

In this work, we study theoretically and numerically new implementational forms of the image-wave... more In this work, we study theoretically and numerically new implementational forms of the image-wave equation for depth remigration. This is a partial second-order differential equation similar to the acoustic wave equation. We determine, additionally to consistency and stability, the conditions for dispersion and dissipation of six finite-difference schemes for this equation in different forms, obtained by a change of variables. These conditions cannot be simultaneously satisfied, i.e., a precise result is not easily obtained. Numerical tests confirm the theoretical stability results for three of the investigated schemes but fail for the others. Of the tested schemes, the ones forward in the velocity variable and forward or backward in depth were the most useful ones in the sense that they satisfy the theoretical predictions about their stability and can be utilized to realize the image-wave propagation, the former for increasing velocities and the latter for decreasing velocities.

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2.5 D Finite-Difference Solution Of The Acoustic Wave Equation

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Curvelet Denoising for Preconditioning of 2D Poststack Seismic Data Inversion: Application to Data from the Marimbá Oil Field, Offshore Brazil

Pure and Applied Geophysics

Seismic inversion methods are highly sensitive to noise present in the data set. Most application... more Seismic inversion methods are highly sensitive to noise present in the data set. Most applications today attempt alternatives to achieve an amplification of the real signal, which corresponds to the subsurface structures, over the noise. The need to enhance the signal-to-noise ratio (SNR) motivated researchers do develop increasingly sophisticated denoising methods and combine them into other techniques. While some methodologies operate on a single scale, the curvelet transform established itself as multi-scale transform useful to decompose the seismic signals into multi-resolution elements. In this study, we evaluate the benefits of curvelet denoising as a preconditioning method for poststack seismic data in a 2D acoustic inversion processing using a Bayesian framework. Our tests on the Marmousi model and a real data set from a Brazilian offshore Basin have shown that the curvelet thresholding method can be successfully applied for random-noise elimination. Even the use of a hard global threshold led to improvements in the deepest parts. However, we observed a decrease of the SNR in the presence of soft rocks with pronounced absorption as they are typical in the shallowest regions. Future work will have to show whether alternatives that ensure a more robust way of selecting the coefficients can take into account the wavelength change with depth.

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Robust time-domain migration velocity analysis methods for initial-model building in a full waveform tomography workflow

Proceedings of the 7 Simpósio Brasileiro de Geofísica, 2016

Full-waveform tomography (FWT) is notorious for its strong dependence on the initial model. We pr... more Full-waveform tomography (FWT) is notorious for its strong dependence on the initial model. We present a workflow for the construction of initial velocity-models for FWT methods consisting of automatic time-migration velocity analysis by means of double multi-stack migration, followed by timeto-depth conversion by image-ray wavefront propagation. Evaluation of the converted velocity model as an initial velocity model in an acoustic FWT process indicates the potential of using a combination of these methods to achieve a fully automatic tool for initial-model building in a FWT workflow. Our tests on a modified version of the Marmousi-2 model have shown that correct background velocity information can be successfully extracted from automatic time-domain migration velocity analysis even in media where time-migration cannot provide satisfactory seismic images.

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Time window-size dependence analysis for the minimum semblance approach

Proceedings of the 7 Simpósio Brasileiro de Geofísica, 2016

Este texto foi preparado para a apresentação no Simpósio Brasileiro de Geofísica, Ouro Preto, 25 ... more Este texto foi preparado para a apresentação no Simpósio Brasileiro de Geofísica, Ouro Preto, 25 a 27 de outubro de 2016. Seu conteúdo foi revisado pelo Comitê Técnico do VII SimBGf, mas não necessariamente representa a opinião da SBGf ou de seus associados.É proibida a reprodução total ou parcial deste material para propósitos comerciais sem prévia autorização da SBGf.

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Seismic data inversion with curvelet denoising preconditioning

15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017, 2017

Contents of this paper were reviewed by the Technical Committee of the 15 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 15 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.

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$Research paper thumbnail of Predictions of seismic velocity models (time and depth) by combining diffraction filter and residual diffraction moveout$

Predictions of seismic velocity models (time and depth) by combining diffraction filter and residual diffraction moveout

14th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 3-6 August 2015, 2015

Minimum semblance: A new coherence measure to improve resolution of semblance sections

14th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 3-6 August 2015, 2015

A Comparison of Imaging Conditions for Wave-Equation Shot-Profile Migration

10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, Nov 23, 2007

The application of a deconvolution imaging condition in wave-equation shot-profile migration is i... more The application of a deconvolution imaging condition in wave-equation shot-profile migration is important to provide illumination compensation and amplitude recovery. Particularly if the aim is to successfully recover a measure of the medium reflectivity, an imaging condition that destroys amplitudes is unacceptable. We study a set of imaging conditions with illumination compensation. The imaging conditions are evaluated by the quality of the output amplitudes and artifacts produced. In numerical experiments using a vertically inhomogeneous velocity model, the best of all imaging conditions we tested is the one that divides the crosscorrelation of upgoing and downgoing wavefields by the autocorrelation of the downgoing wavefield, also known as the illumination map. In an application to Marmousi data, unconditional division by autocorrelation turned out to be unstable. Effective stabilization was achieved by smoothing the illumination map.

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Signatura: BR9406358

Resolução da Equação de Onda Através da Teoria dos Raios

Three-dimensional complex padé FD migration: Splitting and corrections

Three-dimensional wave-equation migration techniques are still quite expensive because of the hug... more Three-dimensional wave-equation migration techniques are still quite expensive because of the huge matrices that need to be inverted. Several techniques have been proposed to reduce this cost by splitting the full 3D problem into a sequence of 2D problems. To reduce errors, the Li correction is applied at regular multiples of depth extrapolation increment. We compare the performance of splitting techniques in wave propagation for 3D finite-difference (FD) migration in terms of image quality and computational cost. We study the behaviour of the complex Padé approximation in combination with two-and alternating four-way splitting, that is, splitting into the coordinate directions at one depth and the diagonal directions at the next depth level. We also extend the Li correction for use with the complex Padé expansion and diagonal directions. From numerical examples in inhomogeneous media, we conclude that alternate four-way splitting is the most cost-effective strategy to reduce numerical anisotropy in complex Padé 3D FD migration.

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Offset-continuation trajectory stack

SEG Technical Program Expanded Abstracts 2013, 2013

We introduce a data-driven stacking technique that transforms 2D/2.5D prestack multicoverage data... more We introduce a data-driven stacking technique that transforms 2D/2.5D prestack multicoverage data into a commonoffset (CO) section. We refer to this new process, which is based on the offset-continuation operation (OCO), as offsetcontinuation trajectory stacking or briefly OCT stack. Similarly to the CMP and CRS stacks, this new method does not rely on an a-priori velocity model but provides velocity information itself. The original offset-continuation-operation (OCO) method is a seismic configuration transform designed to simulate a seismic section as if obtained with a certain source-receiver offset using the data measured with another offset. Since an OCO depends on the velocity model used in the process, it can be combined with stacking techniques for a set of models, thus allowing for the extraction of velocity information. The algorithm is based on so-called OCO trajectories, which are related to the concepts of image waves and velocity rays. We theoretically derive the OCO trajectories from the kinematic properties of OCO image waves that describe the continuous transformation of the common-offset reflection event from one offset to another. Based on OCO trajectories, we then formulate a horizon-based velocity-analysis method, where root mean square (RMS) velocities and local event slopes are determined by stacking along event horizons. A numerical example demonstrates the feasibility of the method.

Amélia Novais

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