Transmission compensated primary reflection retrieval in the data domain and consequences for imaging

We have developed a scheme that retrieves primary reflections in the two-way traveltime domain by filtering the data. The data have their own filter that removes internal multiple reflections, whereas the amplitudes of the retrieved primary reflections are compensated for two-way transmission losses. Application of the filter does not require any model information. It consists of convolutions and correlations of the data with itself. A truncation in the time domain is applied after each convolution or correlation. The retrieved data set can be used as the input to construct a better velocity model than the one that would be obtained by working directly with the original data and to construct an enhanced subsurface image. Two 2D numerical examples indicate the effectiveness of the method. We have studied bandwidth limitations by analyzing the effects of a thin layer. The presence of refracted and scattered waves is a known limitation of the method, and we studied it as well. Our analysis indicates that a thin layer is treated as a more complicated reflector, and internal multiple reflections related to the thin layer are properly removed. We found that the presence of refracted and scattered waves generates artifacts in the retrieved data.

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Data-driven internal multiple elimination and its consequences for imaging: A comparison of strategies

Geophysics ◽

10.1190/geo2018-0817.1 ◽

2019 ◽

Vol 84 (5) ◽

pp. S365-S372 ◽

Cited By ~ 5

Author(s):

Lele Zhang ◽

Jan Thorbecke ◽

Kees Wapenaar ◽

Evert Slob

Keyword(s):

Inverse Scattering ◽

Computational Cost ◽

Multiple Reflection ◽

Data Driven ◽

Transmission Losses ◽

Multiple Reflections ◽

Data Set ◽

Numerical Examples ◽

Inverse Scattering Series ◽

Multiple Elimination

We have compared three data-driven internal multiple reflection elimination schemes derived from the Marchenko equations and inverse scattering series (ISS). The two schemes derived from Marchenko equations are similar but use different truncation operators. The first scheme creates a new data set without internal multiple reflections. The second scheme does the same and compensates for transmission losses in the primary reflections. The scheme derived from ISS is equal to the result after the first iteration of the first Marchenko-based scheme. It can attenuate internal multiple reflections with residuals. We evaluate the success of these schemes with 2D numerical examples. It is shown that Marchenko-based data-driven schemes are relatively more robust for internal multiple reflection elimination at a higher computational cost.

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Free-surface and internal multiple elimination in one step without adaptive subtraction

Geophysics ◽

10.1190/geo2018-0548.1 ◽

2019 ◽

Vol 84 (1) ◽

pp. A7-A11 ◽

Cited By ~ 13

Author(s):

Lele Zhang ◽

Evert Slob

Keyword(s):

Free Surface ◽

Velocity Model ◽

Original Data ◽

Time Instant ◽

Scattering Media ◽

Multiple Reflections ◽

Data Set ◽

Surface Reflection ◽

Wide Range ◽

One Step

We have derived a scheme for retrieving the primary reflections from the acoustic surface-reflection response by eliminating the free-surface and internal multiple reflections in one step. This scheme does not require model information and adaptive subtraction. It consists only of the reflection response as a correlation and convolution operator that acts on an intermediate wavefield from which we compute and capture the primary reflections. For each time instant, we keep one value for each source-receiver pair and store it in the new data set. The resulting data set contains only primary reflections, and from this data set, a better velocity model can be built than from the original data set. A conventional migration scheme can then be used to compute an artifact-free image of the medium. We evaluated the success of the method with a 2D numerical example. The method can have a wide range of applications in 3D strongly scattering media that are accessible from one side only.

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Implementation of the Marchenko Multiple Elimination algorithm

Geophysics ◽

10.1190/geo2020-0196.1 ◽

2020 ◽

pp. 1-54

Author(s):

Jan Thorbecke ◽

Lele Zhang ◽

Kees Wapenaar ◽

Evert Slob

Keyword(s):

Time Domain ◽

Neumann Series ◽

Transmission Losses ◽

Multiple Reflections ◽

Elimination Algorithm ◽

Domain Truncation ◽

Internal Multiples ◽

The Time Domain ◽

Multiple Elimination ◽

Elimination Scheme

The Marchenko multiple elimination and transmission compensation schemes retrieve primary reflections in the two-way traveltime domain without model information or using adaptive subtraction. Both schemes are derived from projected Marchenko equations and similar to each other, but use different time-domain truncation operators. The Marchenko multiple elimination scheme retrieves a new dataset without internal multiple reflections. The transmission compensated Marchenko multiple elimination scheme does the same and additionally compensates for transmission losses in the primary reflections. Both schemes can be solved with an iterative algorithm based on a Neumann series. At each iteration, a convolution or correlation between the projected focusing function and the measured reflection response are performed and after each convolution or correlation, a truncation in the time domain is applied. After convergence, the resulting projected focusing function is used for retrieving the transmission compensated primary reflections and the projected Green’s function is used for the physical primary reflections. We demonstrate that internal multiples are removed by using time-windowed input data that only contain primary reflections. We evaluate both schemes in detail and develop an iterative implementation that reproduces the presented numerical examples. The software is part of our open-source suite of programs and fits into the Seismic Unix software suite of the Colorado School of Mines.

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Frequency-domain wave-equation traveltime inversion with a monofrequency component

Geophysics ◽

10.1190/geo2020-0708.1 ◽

2021 ◽

Vol 86 (6) ◽

pp. R913-R926

Author(s):

Jianhua Wang ◽

Jizhong Yang ◽

Liangguo Dong ◽

Yuzhu Liu

Keyword(s):

Wave Equation ◽

Frequency Domain ◽

Time Domain ◽

Computational Cost ◽

Velocity Model ◽

Receiver Side ◽

Data Set ◽

Traveltime Inversion ◽

Velocity Models ◽

The Time Domain

Wave-equation traveltime inversion (WTI) is a useful tool for background velocity model building. It is generally formulated and implemented in the time domain, in which the gradient is calculated by temporally crosscorrelating the source- and receiver-side wavefields. The time-domain source-side snapshots are either stored in memory or are reconstructed through back propagation. The memory requirements and computational cost of WTI are thus prohibitively expensive, especially for 3D applications. To partially alleviate this problem, we provide an implementation of WTI in the frequency domain with a monofrequency component. Because only one frequency is used, it is affordable to directly store the source- and receiver-side wavefields in memory. There is no need for wavefield reconstruction during gradient calculation. In such a way, we have dramatically reduced the memory requirements and computational cost compared with the traditional time-domain WTI realization. For practical implementation, the frequency-domain wavefield is calculated by time-domain finite-difference forward modeling and is transformed to the frequency domain by an on-the-fly discrete Fourier transform. Numerical examples on a simple lateral periodic velocity model and the Marmousi model demonstrate that our method can obtain accurate background velocity models comparable with those from time-domain WTI and frequency-domain WTI with multiple frequencies. A field data set test indicates that our method obtains a background velocity model that well predicts the seismic wave traveltime.

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Migration velocity analysis based on focusing diffractions generated using the CRS wavefront attributes: Application to real land data

Geophysics ◽

10.1190/geo2020-0696.1 ◽

2021 ◽

pp. 1-50

Author(s):

German Garabito ◽

José Silas dos Santos Silva ◽

Williams Lima

Keyword(s):

Time Domain ◽

Real Data ◽

Normal Incidence ◽

Velocity Model ◽

Migration Velocity ◽

Velocity Analysis ◽

Velocity Models ◽

Time Migration ◽

Migration Velocity Analysis ◽

The Time Domain

In land seismic data processing, the prestack time migration (PSTM) image remains the standard imaging output, but a reliable migrated image of the subsurface depends on the accuracy of the migration velocity model. We have adopted two new algorithms for time-domain migration velocity analysis based on wavefield attributes of the common-reflection-surface (CRS) stack method. These attributes, extracted from multicoverage data, were successfully applied to build the velocity model in the depth domain through tomographic inversion of the normal-incidence-point (NIP) wave. However, there is no practical and reliable method for determining an accurate and geologically consistent time-migration velocity model from these CRS attributes. We introduce an interactive method to determine the migration velocity model in the time domain based on the application of NIP wave attributes and the CRS stacking operator for diffractions, to generate synthetic diffractions on the reflection events of the zero-offset (ZO) CRS stacked section. In the ZO data with diffractions, the poststack time migration (post-STM) is applied with a set of constant velocities, and the migration velocities are then selected through a focusing analysis of the simulated diffractions. We also introduce an algorithm to automatically calculate the migration velocity model from the CRS attributes picked for the main reflection events in the ZO data. We determine the precision of our diffraction focusing velocity analysis and the automatic velocity calculation algorithms using two synthetic models. We also applied them to real 2D land data with low quality and low fold to estimate the time-domain migration velocity model. The velocity models obtained through our methods were validated by applying them in the Kirchhoff PSTM of real data, in which the velocity model from the diffraction focusing analysis provided significant improvements in the quality of the migrated image compared to the legacy image and to the migrated image obtained using the automatically calculated velocity model.

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Recurrence Plot-Based Approach for Cardiac Arrhythmia Classification Using Inception-ResNet-v2

Frontiers in Physiology ◽

10.3389/fphys.2021.648950 ◽

2021 ◽

Vol 12 ◽

Author(s):

Hua Zhang ◽

Chengyu Liu ◽

Zhimin Zhang ◽

Yujie Xing ◽

Xinwen Liu ◽

...

Keyword(s):

Cardiac Arrhythmia ◽

Time Domain ◽

Original Data ◽

Classification Problem ◽

Recurrence Plot ◽

Two Dimensions ◽

Time Frequency ◽

Ecg Signals ◽

Physiological Signal ◽

The Time Domain

The present study addresses the cardiac arrhythmia (CA) classification problem using the deep learning (DL)-based method for electrocardiography (ECG) data analysis. Recently, various DL techniques have been utilized to classify arrhythmias, with one typical approach to developing a one-dimensional (1D) convolutional neural network (CNN) model to handle the ECG signals in the time domain. Although the CA classification in the time domain is very prevalent, current methods’ performances are still not robust or satisfactory. This study aims to develop a solution for CA classification in two dimensions by introducing the recurrence plot (RP) combined with an Inception-ResNet-v2 network. The proposed method for nine types of CA classification was tested on the 1st China Physiological Signal Challenge 2018 dataset. During implementation, the optimal leads (lead II and lead aVR) were selected, and then 1D ECG segments were transformed into 2D texture images by the RP approach. These RP-based images as input signals were passed into the Inception-ResNet-v2 for CA classification. In the CPSC, Georgia, and the PTB_XL ECG databases of the PhysioNet/Computing in Cardiology Challenge 2020, the RP-based method achieved an average F1-score of 0.8521, 0.8529, and 0.8862, respectively. The results suggested the excellent generalization ability of the proposed method. To further assess the performance of the proposed method, we compared the 2D RP-image-based solution with the published 1D ECG-based works on the same dataset. Also, it was compared with two traditional ECG transform into 2D image methods, including the time waveform of the ECG recordings and time-frequency images based on continuous wavelet transform (CWT). The proposed method achieved the highest average F1-score of 0.844, with only two leads of the 12-lead ECG original data, which outperformed other works. Therefore, the promising results indicate that the 2D RP-based method has a high clinical potential for CA classification using fewer lead ECG signals.

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Statement of absorbing Mur boundary conditions of the first order of accuracy for solving problems of electrodynamics by the method of finite differences in the time domain

Radioengineering ◽

10.18127/j00338486-202108-07 ◽

2021 ◽

Vol 8 ◽

pp. 57-68

Author(s):

R.Yu. Borodulin ◽

N.O. Lukyanov

Keyword(s):

Boundary Conditions ◽

Time Domain ◽

Correct Choice ◽

Absorbing Boundary Conditions ◽

Practical Significance ◽

Stable Operation ◽

Absorbing Boundary ◽

Spherical Waves ◽

The One ◽

The Time Domain

Problem statement. The accuracy and convergence of calculations for solving problems of electrodynamics by the finite difference method in the time domain significantly depends on the correct choice of parameters and the correct setting of the absorbing boundary conditions (ABC). Two main types of absorbing boundary conditions are known: Mur ABC; Beranger ABC. It is believed that the Mur ABC is less effective at absorbing spherical waves than the Beranger ABC, but they do not require the introduction of additional parameters (the so-called "Beranger fields"), which simplifies the implementation of program code and saves computer RAM. Calculations have shown that the efficiency of the Mur ABC will depend on their thickness. On the one hand, an increase in the thickness of the ABC layers will lead to an increase in the accuracy of calculations, on the other hand, to an increase in the size of the calculation area and, as a result, an increase in RAM. The problem arises of determining the criterion for evaluating the efficiency of ABC to determine their optimal thickness. Goal. Identification of new factors that make it possible to use the Mur ABC as efficiently as the Beranger ABC, while significantly saving computer resources. Result. The expressions for the ABC are presented, taking into account the interaction of all components of the electromagnetic field within a single cell of the FDTD. Calculations of the reflection coefficient – a criterion for evaluating the efficiency of the ABC, are presented. Practical significance. Calculations are presented that allow automating the selection of ABC parameters for their stable operation in solving electrodynamic problems.

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Application of Laplace Domain Waveform Inversion to Cross-Hole Radar Data

Remote Sensing ◽

10.3390/rs11161839 ◽

2019 ◽

Vol 11 (16) ◽

pp. 1839

Author(s):

Xu Meng ◽

Sixin Liu ◽

Yi Xu ◽

Lei Fu

Keyword(s):

Time Domain ◽

Waveform Inversion ◽

Radar Data ◽

Dominant Frequency ◽

Data Set ◽

Laplace Domain ◽

Full Waveform ◽

Highly Nonlinear ◽

The Time Domain ◽

Ground Penetrating

Full waveform inversion (FWI) can yield high resolution images and has been applied in Ground Penetrating Radar (GPR) for around 20 years. However, appropriate selection of the initial models is important in FWI because such an inversion is highly nonlinear. The conventional way to obtain the initial models for GPR FWI is ray-based tomogram inversion which suffers from several inherent shortcomings. In this paper, we develop a Laplace domain waveform inversion to obtain initial models for the time domain FWI. The gradient expression of the Laplace domain waveform inversion is deduced via the derivation of a logarithmic object function. Permittivity and conductivity are updated by using the conjugate gradient method. Using synthetic examples, we found that the value of the damping constant in the inversion cannot be too large or too small compared to the dominant frequency of the radar data. The synthetic examples demonstrate that the Laplace domain waveform inversion provide slightly better initial models for the time domain FWI than the ray-based inversion. Finally, we successfully applied the algorithm to one field data set, and the inverted results of the Laplace-based FWI show more details than that of the ray-based FWI.

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Formation and breakdown of the alliance between state and civic forces in post-2013 Egypt: a state-in-society approach

Journal of Humanities and Applied Social Sciences ◽

10.1108/jhass-01-2020-0015 ◽

2020 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Mazen Hassan

Keyword(s):

Arab World ◽

Public Attitudes ◽

Original Data ◽

Threat Perception ◽

Data Set ◽

Content Type ◽

The Status ◽

State Actors ◽

Elite Interviews ◽

The One

Purpose This paper aims to examine why the alliance formed between non-Islamist forces and state actors to oust Mohamed Morsi from power in 2013 broke down quickly. Design/methodology/approach This paper makes use of original data set derived from three waves of surveys fielded in 2011, 2014 and 2015 that ask questions about public threat perception. Around 10 elite interviews were also conducted to further test the study’s hypothesis. Findings On the one hand, non-Islamists, civic forces challenged the status and interests of state actors in a way that made state actors view them with heightened distrust. On the other, many civic forces, in face of high threat perception, prioritized law during and order after Morsi’s removal, driven – at least partly – by shifts in public attitudes. Originality/value Many views look at transitions in the Arab world from the angle of how Islamists interact with traditional power holders. Such an approach, however, could be reductionist in many ways because it disregards civic forces. This is a point this paper seeks to address.

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Simulating High Mode Vortex Induced Vibration of Riser in Linear Sheared Current Using an Empirical Time Domain Model

Volume 1: Offshore Technology ◽

10.1115/omae2020-18271 ◽

2020 ◽

Author(s):

Sang Woo Kim ◽

Svein Sævik ◽

Jie Wu

Keyword(s):

Frequency Domain ◽

Vortex Shedding ◽

Time Domain ◽

Structural Model ◽

Cross Flow ◽

Domain Model ◽

Vortex Induced Vibrations ◽

The One ◽

The Time Domain ◽

Empirical Coefficients

Abstract This paper addresses the performance evaluation of an empirical time domain Vortex Induced Vibrations (VIV) model which has been developed for several years at NTNU. Unlike the frequency domain which is the existing VIV analysis method, the time domain model introduces new vortex shedding force terms to the well known Morison equation. The extra load terms are based on the relative velocity, a synchronization model and additional empirical coefficients that describe the hydrodynamic forces due to cross-flow (CF) and In-line (IL) vortex shedding. These hydrodynamic coefficients have been tuned to fit experimental data and by considering the results from the one of existing frequency domain VIV programs, VIVANA, which is widely used for industrial design. The feature of the time domain model is that it enables to include the structural non-linearity, such as variable tension, and time-varying flow. The robustness of the new model’s features has been validated by comparing the test results in previous researches. However, the riser used in experiments has a relatively small length/diameter (L/D) ratio. It implies that there is a need for more validation to make it applicable to real riser design. In this study, the time domain VIV model is applied to perform correlation studies against the Hanøytangen experiment data for the case of linear sheared current at a large L/D ratio. The main comparison has been made with respect to the maximum fatigue damage and dominating frequency for each test condition. The results show the time domain model showed reasonable accuracy with respect to the experimental and VIVANA. The discrepancy with regard to experiment results needs to be further studied with a non-linear structural model.

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