Migration Imaging Research Articles

Impacts from concrete microstructure and surface on the settlement of sessile organisms affecting chloride attack

This study investigates combined protective and negative effects of two sessile organism groups: calcareous-based sessile invertebrates, and root-spreading botanic life forms. A series of concrete cylinders were deployed on the testing site to check how surface properties and biological attachments contribute to chloride penetration. The study methods included chloride migration tests, EPMA (SEM-WDX), and image analysis of the specimen surfaces. The findings indicate that the smooth surface-controlled concrete with GGBS exhibited decent quantities of barnacle and oyster while limiting the area settled by algae. Thus, surface treatment could be a promising solution for recruiting more intertidal species with protective effects.

Optimizing the wavefield storage strategy in reflection-acoustic logging reverse-time migration

In this paper, wavefield storage optimization strategies are discussed with respect to reverse-time migration (RTM) imaging in reflection-acoustic logging, considering the problem of massive wavefield data storage in RTM itself. In doing so, two optimization methods are proposed and implemented to avoid wavefield storage. Firstly, the RTM based on the excitation-amplitude imaging condition uses the excitation time to judge the imaging time, and accordingly, we only need to store a small part of wavefield, such as the wavefield data of dozens of time points, the instances prove that they can even be imaged by only two time points. The traditional RTM usually needs to store the wavefield data of thousands of time points, compared with which the data storage can be reduced by tens or even thousands of times. Secondly, the RTM based on the random boundary uses the idea that the wavefield scatters rather than reflects in a random medium to reconstruct the wavefield source and thereby directly avoid storing the forward wavefield data. Numerical examples show that compared with other migration algorithms and the traditional RTM, both methods can effectively reduce wavefield data storage as well as improve data-processing efficiency while ensuring imaging accuracy, thereby providing the means for high-efficiency and high-precision imaging of fractures and caves by boreholes.

Polarization Migration of Multi-component Seismic Data for Survey in the Tunnel of Mountain Cities

With the development of transportation in the west of China, tunnel construction in mountain cities is becoming very important and widespread. Tunneling safety in the tunnels is usually controlled by faults, and the advanced prediction of faults by seismic detection method has become a research hotspot in the field of engineering geophysics. Unlike seismic exploration on the ground, the sources and receivers are not properly arranged due to the limitation of the tunnel detection space, so as to cause migration artifacts problem in the process of advanced migration imaging. The problem results in inaccurate imaging of the faults. To solve the problem, this paper proposed a new polarization migration method. The method makes use of the polarization characteristic of three-component seismic signals. The principal polarization direction is calculated by Hilbert transform and complex covariance matrix analysis. A weighted function of the principal polarization direction factor is incorporated into the migration calculation. To verify the effectiveness of the polarization migration method, this paper carries out numerical simulations. Test results demonstrate that the artifacts are eliminated by the polarization migration, and occurrence parameters of faults, such as dip and trend are calculated accurately. The field detection case shows that seismic advanced prediction which is based on polarization migration provided parameters of faults in the front of the tunnel face with 100m, and the distance error is less than 2m, and the dip error is less than 3°, which ensures efficient and safe construction of tunneling.

Image domain least-squares migration with a Hessian matrix estimated by non-stationary matching filters

AbstractAssuming that an accurate background velocity is obtained, least-squares migration (LSM) can be used to estimate underground reflectivity. LSM can be implemented in either the data domain or image domain. The data domain LSM (DDLSM) is not very practical because of its huge computational cost and slow convergence rate. The image domain LSM (IDLSM) might be a flexible alternative if estimating the Hessian matrix using a cheap and accurate approach. It has practical potential to analyse convenient Hessian approximation methods because the Hessian matrix is too huge to compute and save. In this paper, the Hessian matrix is approximated with non-stationary matching filters. The filters are calculated to match the conventional migration image to the demigration/remigration image. The two images are linked by the Hessian matrix. An image deblurring problem is solved with the estimated filters for the IDLSM result. The combined sparse and total variation regularisations are used to produce accurate and reasonable inversion results. The numerical experiments based on part of Sigsbee model, Marmousi model and a 2D field data set illustrate that the non-stationary matching filters can give a good approximation for the Hessian matrix, and the results of the image deblurring problem with combined regularisations can provide high-resolution and true-amplitude reflectivity estimations.

Factorization method versus migration imaging in a waveguide

We present a comparative study of two qualitative imaging methods in an acoustic waveguide with sound hard walls. The waveguide terminates at one end and contains unknown obstacles of compact support, to be determined from data gathered by an array of sensors that probe the obstacles with waves and measure the scattered response. The first imaging method, known as the factorization method, is based on the factorization of the far field operator. It is designed to image at single frequency and estimates the support of the obstacles by a Picard range criterion. The second imaging method, known as migration, works either with one or multiple frequencies. It forms an image by backpropagating the measured scattered wave to the search points, using the Green’s function in the empty waveguide. We study the connection between these methods with analysis and numerical simulations.

RETRACTED: LSAMP-AS1 binds to microRNA-183-5p to suppress the progression of prostate cancer by up-regulating the tumor suppressor DCN.

Background: Prostate cancer (PCa) is a leading cause of cancer-related death in males. Aberrant expression of long noncoding RNAs (lncRNAs) is frequently reported in human malignancies. This study was performed to explore the role of LSAMP-AS1 in epithelial-mesenchymal transition (EMT), proliferation, migration and invasion of PCa cells.Methods: Initially, the differentially expressed lncRNAs in PCa were screened out by microarray analysis. The clinicopathological and prognostic significance of LSAMP-AS1 was evaluated. LSAMP-AS1 was over-expressed or silenced to investigate the roles in EMT, proliferation, migration and invasion of PCa cells. Moreover, the relationships between LSAMP-AS1 and miR-183–5p, as well as miR-183–5p and decorin (DCN) were characterized. The tumorigenicity of PCa cells was verified in nude mice.Results: LSAMP-AS1 was poorly expressed in PCa tissues and cells. Low expression of LSAMP-AS1 was indicative of poor overall survival and disease-free survival, and related to Gleason score, TNM stage, and risk stratification. Over-expressed LSAMP-AS1 inhibited EMT, proliferation, migration and invasion of PCa cells, as well as tumor growth in nude mice. Meanwhile, over-expression of LSAMP-AS1 resulted in up-regulation of E-cadherin and down-regulation of Vimentin, N-cadherin, Ki67, PCNA, MMP-2, MMP-9, Ezrin and Fascin. Notably, LSAMP-AS1 competitively bound to miR-183–5p which directly targets DCN. It was confirmed that the inhibitory effect of LSAMP-AS1 on PCa cells was achieved by binding to miR-183–5p, thus promoting the expression of DCN.Conclusion: LSAMP-AS1 up-regulates the DCN gene by competitively binding to miR-183–5p, thus inhibiting EMT, proliferation, migration and invasion of PCa cells.

Least-squares reverse time migration in the presence of velocity errors

Least-squares reverse time migration (LSRTM), which aims to match the modeled data with the observed data in an iterative inversion procedure, is very sensitive to the accuracy of the migration velocity model. If the migration velocity model contains errors, the final migration image may be defocused and incoherent. We have used an LSRTM scheme based on the subsurface offset extended imaging condition, least-squares extended reverse time migration (LSERTM), to provide a better solution when large velocity errors exist. By introducing an extra dimension in the image space, LSERTM can fit the observed data even when significant errors are present in the migration velocity model. We further investigate this property and find that after stacking the extended migration images along the subsurface offset axis within the theoretical lateral resolution limit, we can obtain an image with better coherency and fewer migration artifacts. Using multiple numerical examples, we demonstrate that our method provides superior inversion results compared to conventional LSRTM when the bulk velocity errors are as large as 10%.

The Western Australia Modeling project — Part 1: Geomodel building

A key goal in industry and academic seismic research is overcoming long-standing imaging, inversion, and interpretation challenges. One way to address these challenges is to develop a realistic 3D geomodel constrained by local-to-regional geologic, petrophysical, and seismic data. Such a geomodel can serve as a benchmark for numerical experiments that help users to better understand the key factors underlying — and devise novel solutions to — these exploration and development challenges. We have developed a two-part case study on the Western Australia (WA) Modeling (WAMo) project, which discusses the development and validation of a detailed large-scale geomodel of part of the Northern Carnarvon Basin (NCB) located on WA’s North West Shelf. Based on the existing regional geologic, petrophysical, and 3D seismic data, we (1) develop the 3D geomodel’s tectonostratigraphic surfaces, (2) populate the intervening volumes with representative geologic facies, lithologies, and layering as well as complex modular 3D geobodies, and (3) generate petrophysical realizations that are well-matched to borehole observations point-wise and in terms of vertical and lateral trends. The resulting 3D WAMo geomodel is geologically and petrophysically realistic, representative of short- and long-wavefield features commonly observed in the NCB, and leads to an upscaled viscoelastic model well-suited for high-resolution 3D seismic modeling studies. In the companion paper, we study WAMo seismic modeling results that demonstrate the quality of the WAMo geomodel for generating shot gathers and migration images that are highly realistic and directly comparable with those observed in NCB field data.

An efficient vector elastic reverse time migration method in the hybrid time and frequency domain for anisotropic media

Vector elastic reverse time migration (ERTM) produces subsurface elastic images with correct polarities using multicomponent seismic data. However, the decomposition of elastic wavefields into vector P- and S-wavefields is computationally expensive, particularly in heterogeneous and complex anisotropic media. We have developed a computationally efficient vector ERTM method in the hybrid time and frequency domain by combining three existing techniques. Rather than decomposing elastic wavefields into vector qP- and qS-wavefields during time-domain wavefield propagation, we conduct the wavefield decomposition in the frequency domain for several selected frequencies. In general, the number of selected frequencies needed for migration imaging is much smaller than the number of time steps during forward and backward wavefield propagation, leading to greatly reduced computational costs associated with the qP-/qS-wavefield vector separation in complex heterogeneous anisotropic media. We further combine an implicit directional wavefield separation into the vector ERTM to enhance the image quality. The numerical results demonstrate that our method produces high-quality elastic-wave migration images with notably reduced computational costs compared to the conventional vector ERTM method.

Advances in active acoustic ranging

Recent advances in the processing and interpretation of sonic imaging surveys warrant a fresh look at the performance of active acoustic ranging for locating wellbores. The interpretation of results from sonic imaging surveys typically has been done in workflows similar to classic seismic interpretation, where the data are projected into a 2D plane and reflective features are picked. These sonic imaging workflows require significant time and expertise to execute. The reflected arrival events typically are obscured by higher amplitude borehole modes, and the migration workflow needs numerous critical parameter choices that require interpreting the raypath type and azimuth of the reflected arrivals. When used for acoustic ranging, additional challenges are present, particularly in situations where the logging tool rotates and the relative position of the target well changes with depth. This may occur when the logging or target well trajectories have a curved shape, since determining the direction and distance to the target well then requires careful interpretation of migration image amplitudes. We demonstrate how a newly developed automated approach to the interpretation of sonic imaging data helps improve accuracy and removes interpreter bias while simplifying the processing chain and reducing turnaround time. We compare our results to what has been obtained previously by using the same data set. We achieve a marked improvement in accuracy and consistency using this new technique.

Correction to: The 3'UTR of the pseudogene CYP4Z2P promotes tumor angiogenesis in breast cancer by acting as a ceRNA for CYP4Z1.

After publication of this article [1], it came to our attention that there was an error in Fig. 4b and 4c. In Fig.4b, the migration images of vector groups were incorrect based on this error, the authors re-constructed the migration experiments of Fig. 4b, and the consistent results were obtained. In Fig. 4c, the tube formation image of the Z2P-UTR-siRNA&Z1-UTR group (MCF-7) of Fig. 7d was accidentally misused in control group (MCF-7) and vector group (MCF-7) of Fig. 4c. The corrected Fig. 4 is provided below. This error did not impact the conclusions of the article. The authors apologize for this error.

Joint refraction traveltime tomography and migration for multilayer near-surface imaging

In near-surface velocity structure estimation, first-arrival traveltime tomography tends to produce a smooth velocity model. If the shallow structures include a weathering layer over high-velocity bedrock, first-arrival traveltime tomography may fail to recover the sharp interface. However, with the same traveltime data, refraction traveltime migration proves to be an effective tool for accurately mapping the refractor. The approach downward continues the refraction traveltime curves and produces an image (position) of the refractor for a given overburden velocity model. We first assess the validity of the refraction traveltime migration method and analyze its uncertainties with a simple model. We then develop a multilayer refraction traveltime migration method and apply the migration image to constrain traveltime tomographic inversion by imposing discontinuities at the refraction interfaces in model regularization. In each subsequent iteration, the shape of the migrated refractors and the velocity model are simultaneously updated. The synthetic tests indicate that the joint inversion method performs better than the conventional first-arrival traveltime tomography method with Tikhonov regularization and the delay-time method in reconstructing near-surface models with high-velocity contrasts. In application to field data, this method produces a more accurately resolved velocity model, which improves the quality of common midpoint stacking by making long-wavelength static corrections.

Research on Fast Image Style Transformation Based on Residual Network

Image style migration technology refers to the conversion of an image into a similar image to a famous painting style through learning (using a convolutional neural network). The A Neural Algorithm of Artistic Style (NAAS) proposed by Gatys uses the VGG network to design a loss network, and the style migration image is obtained through repeated iterations, and the calculation speed is slow. Li Feifei introduced the residual network on the basis of Gatys, and accelerated the calculation by using the fast connection feature of the residual element. This method has a great improvement in the generation speed but still has room for improvement. This paper proposes improvements for the following two aspects: firstly, the classical residual element structure is adjusted, and the standard convolution is converted into point convolution and deep convolution, which reduces the calculation amount while ensuring the convolution effect; secondly, the loss network is simplified. The fourth and fifth layers in the model are highly consistent in structure, and the style restoration of the two layers is basically the same as the content reconstruction effect. Therefore, the fifth layer is deleted, the redundant parameters are removed, and the parameter amount is reduced. At the same time, the effect of style restoration and content reconstruction is guaranteed.

Acoustic localization using Green’s function retrieval methods and range migration processing

In this work, Green’s function retrieval and frequency-wavenumber methods are employed to enhance array plane-wave beamforming maps for acoustic source localization and range estimation in an outdoor environment. The crosscorrelation and multidimensional deconvolution Green’s function retrieval methods are used to improve the signal-to-noise ratio of the beamforming maps. The Stolt’s frequency-wavenumber migration method is adapted to the plane-wave beamforming map to find the source positions, applying frequency-wavenumber migration image to the Stolt spatial transformation mapping. Open field microphone array measurements of active and passive sources are investigated. Of particular interests are the accuracy of the estimated source position, the effects of multiple sources and the image contrast of the beamforming maps.

3D slowness time coherence for sonic imaging

Although sonic imaging can provide higher resolution images of the near-wellbore region than lower frequency seismic and borehole seismic measurements, many challenges confront its more widespread use. The traditional sonic imaging workflow of first filtering the borehole modes and then migrating the underlying reflected arrival events ignores a critical interpretation step, namely, characterizing these reflected arrivals in terms of their azimuths, raypath types, and other attributes. Furthermore, using sonic imaging results in subsequent modeling and simulation workflows requires determining the 3D coordinates or at least the true dip and azimuth of these near-wellbore reflectors, and feature extraction from noisy 2D sonic imaging migration images cannot provide either of these. To address these interpretation challenges and develop a means of mapping these reflectors without requiring a migration, a central issue that arises is whether we can determine the slowness and propagation direction of a reflected wavefield using a standard array of receiver sensors mounted around the circumference of a tool sonde. To accomplish this task, we have developed 3D slowness time coherence (STC). We combine an automated time pick with a ray-tracing procedure and our 3D STC processing to evaluate the many candidate arrival events that may be present in the filtered waveform measurements, which leads to a 3D map of the reflectors that can be readily integrated into digital models of the surrounding subsurface as well as logs of reflector true dip and azimuth that can be compared with similar logs produced from borehole images.

Passive multiple reverse time migration imaging based on wave decomposition and normalized imaging conditions

With the development of seismic exploration, passive-source seismic data has attracted increasing attention. Ambient noise passive seismic sources exists widely in nature and industrial production. Passive seismic data is important in logging while drilling (LWD), large-scale structural exploration, etc. In this paper, we proposed a passive multiple reverse time migration imaging (PMRTMI) method based on wavefield decomposition and normalized imaging conditions method. This method differs from seismic interferometry in that it can use raw passive seismic data directly in RTM imaging without reconstruction of virtual active gather, and we use the wavefield decomposition method to eliminate the low frequency noise in RTM. Further, the energy normalized imaging condition is used in full wavefield decomposition, which can not only enhance the image quality of both edge and deep information but also overcome the wrong energy problem caused by uneven distribution of passive sources; furthermore, this method exhibits high efficiency. Finally, numerical examples with the Marmousi model show the effectiveness of the method.

Wavelet-domain reverse time migration image enhancement using inversion-based imaging condition

Reverse time migration (RTM) is implemented by solving the two-way wave equation using recorded data as boundary conditions. The full wave equation can simulate wave propagation in all directions; thus, RTM has no dip limitations and is capable of imaging complex structures. Because wavefields are allowed to travel in all directions, the source and receiver wavefields can be scattered back from strong velocity contrasts. The crosscorrelation of head waves, diving waves, and backscattered waves along a raypath can lead to strong artifacts in the RTM image. These artifacts degrade the final image quality. An inversion-based imaging condition that computes the weighted sum of a time derivative image and a spatial gradient image can significantly reduce the RTM artifacts. Based on the multiscale directional selectivity property of the wavelet transform, we have developed a new method to compute the weighting function for the inversion-based imaging condition in the wavelet domain. The unique property of this approach is that the weighting function depends on the spatial locations, wavenumber, and local directions. This multidimensional property allows us to selectively remove the RTM image artifacts while preserving useful energy. We determine the effectiveness of our method for attenuating RTM artifacts using synthetic examples.

Enhancing Subsurface Scatters Using Reflection-Damped Plane-Wave Least-Squares Reverse Time Migration

Subsurface scatters are sometimes masked by reflectors in seismic migration images, because the diffractions are much weaker in energy than the reflections. We propose a novel imaging method, named reflection-damped plane-wave least-squares reverse time migration (RD_PLSRTM), to enhance the scatters in the migration image. We formulate seismic imaging as an inverse problem that minimizes a weighted residual between the modeled and observed seismic data. In the proposed approach, we use the plane-wave destruction filter to separate the diffractions from the reflections in the data residual. A reflection-damped weighting matrix is then used to govern the fitting of the diffractions and the reflections, and therefore emphasize the updates of the scatters. The inverse problem is finally solved by using an iteratively reweighted least-squares (IRLS) algorithm. The proposed method provides a generalized formulation that could be reduced to conventional PLSRTM and PLSRTM of diffractions (PLSRTM_D) by using specific damping factors. We conduct imaging tests on synthetic and field data that prove the superiority of the proposed method over PLSRTM in imaging deep scatters and subsalt scatters. Compared with PLSRTM_D, it could produce high-quality images of not only the scatters but also the reflectors.

Subsurface Reconstruction From GPR Data by 1-D DBIM and RTM in Frequency Domain

This letter presents the joint reconstruction of unknown subsurface structures by the full-wave inversion (FWI) and reverse time migration (RTM) imaging. In the FWI, the 1-D distorted Born iteration method (DBIM) is employed to retrieve the dielectric parameters of the layered subsurface medium by minimizing the difference between measured fields and calculated fields via Frechet derivatives. Based on the inversion results, the RTM is directly performed in the frequency domain to image the buried objects using the ground-penetrating radar (GPR) data. Numerical and laboratory experiments show that the proposed joint method can be used to reconstruct the subsurface structures reliably and efficiently.

Finite element reverse time migration imaging in tunnels using an unstructured mesh

Wave field extrapolation is critical in reverse time migration (RTM). At present, wavefield extrapolation in RTM imaging for tunnels is mostly carried out via the finite difference method. However, complex tunnel models, such as those for karst and fault fracture zones, are constructed using regular grids with straight curves which can easily cause numerical dispersion and reduce imaging accuracy. In this study, the wavefield extrapolation for tunnel RTM was conducted using the finite element method, where an unstructured mesh is employed as the body-fitted partition in a complex model. The Poynting vector calculation equation suitable for the unstructured mesh finite element method was established to suppress low-frequency noise interference. The tunnel space was considered during the wavefield extrapolation to suppress mirror artefacts by using the flexibility of mesh generation. Finally, the influence of the survey layouts (one-sidewall and two-sidewall) on the tunnel imaging results was explored. The RTM results for a simple tunnel model with an inclined interface show that the method based on unstructured meshes can effectively suppress low-frequency noise and mirror artefacts, thus obtaining clearer imaging results. Also, the two-sidewall tunnel survey layout more accurately obtains the real position of the inclined interface ahead of the tunnel face. Complex tunnel numerical modelling and actual data migration results further illustrate the effectiveness of the finite element unstructured mesh method.