Ghost Effect Research Articles

Back to basics on broadband seismic amplitudes, phase and resolution

Marine broadband seismic results typically have observed amplitude spectra that are inconsistent with the earth reflectivity spectra measured from spatially coincident well data. The most notable inconsistency is a visual bias towards stronger ultra-low frequency amplitudes in the 0–10 Hz range on seismic data. Whilst useful in principle for more accurate elastic seismic inversion with less dependence upon low frequency model (LFM) building and for more stable full waveform inversion (FWI), the low frequency bias will degrade seismic resolution if not balanced properly during processing. Furthermore, the observed seismic amplitude spectra on pre-stack data vary with increasing offset and the phase can strongly vary in a frequency-dependent manner. These variations are attributed to three first-order processes: 1. Progressive attenuation of higher frequencies with longer travel paths, 2. NMO stretch, and 3. Offset-dependent tuning, and may easily be compounded by inappropriate parameterization of various processing and imaging steps. A key component of elastic seismic inversion is the extraction and scaling of several angle-dependent and depth-dependent wavelets. These wavelets are ideally independent of the aforementioned processes but inevitably they are not, and the angle ranges used in the inversion impact the significance of NMO stretch and offset-dependent tuning. Even if these various considerations can all be accommodated during processing, the resolution of seismic images is limited by the resolution of the velocity model, the scattering assumptions of the imaging algorithms used, and the a priori information used to constrain imaging and inversion. After reviewing the principles of seismic wavefield propagation in the contemporary context of broadband seismic methods, largely pursued with the ambition of removing sea surface-related ghost effects, I discuss the additional uncertainties introduced into seismic signal processing by broader bandwidth data — notably at the low frequency end. I consider two rather different ‘broadband seismic’ perspectives: 1. The industry must progress towards higher fidelity and resource-consuming measurements of every source event and every receiver measurement in order to effectively deconvolve the ‘system response’ from the data, or, 2. High-end imaging solutions can automatically eliminate the ‘source term’ without requiring detailed source information — assuming that wavefield separation has robustly accounted for dynamic variations in receiver geometry. A longer term consideration of imaging suggests that the classical sequential processing paradigm is in fact dead, that the definition of ‘noise’ is changing, and that advances in hardware are enabling solutions to long-standing challenges with cross-talk artifacts and irregular illumination. The addition of appropriate a priori information into joint migration and inversion allows historical assumptions about the unknown velocity model having a smooth background to be dismissed, and step changes in velocity model resolution may be achievable. I conclude by discussing how higher resolution velocity models will translate to less non-physical efforts in processing that can corrupt pre-stack amplitude, pre-stack phase and (elastic) image resolution.

Global well posedness for the ghost effect system

The aim of this paper is to discuss the issue of global existence of weak solutions of the so called ghost effect system which has been derived recently in [C. D. LEVERMORE, W. SUN, K. TRIVISA, SIAM J. Math. Anal. 2012]. We extend the local existence of solutions proved in [C.D. LEVERMORE, W. SUN, K. TRIVISA, Indiana Univ. J., 2011] to a global existence result. The key tool in this paper is a new functional inequality inspired of what proposed in [A. JÜNGEL, D. MATTHES, SIAM J. Math. Anal., 2008]. Such an inequality being adapted in [D. BRESCH, A. VASSEUR, C. YU, 2016] to be useful for compressible Navier-Stokes equations with degenerate viscosities. Our strategy to prove the global existence of solution builds upon the framework developed in [D. BRESCH, V. GIOVANGILI, E. ZATORSKA, J. Math. Pures Appl., 2015] for low Mach number system.

Stock Prices and Stock Return Volatilities Impliedby the Credit Market

In this article, the author compares equity and credit investors’ opinions on price formation in the equity market. More exactly, he inverts the CreditGrades model in order to back out credit-implied stock prices and stock return volatilities from credit default swap spreads for companies in the DJIA index. The credit-implied stock prices often deviate significantly from actual stock prices over the long term. Meanwhile, their day-to-day movements are significantly correlated with actual stock returns for most firms in the DJIA. In an attempt to demonstrate potential applications of credit-implied stock prices, the author constructs simple “capital structure arbitrage” trading strategies based on past credit-implied prices. These strategies only require the buying and selling of stocks and differ from traditional cross-capital structure strategies by being suitable for retail investors and other investors without access to the credit derivatives market. The credit-implied volatilities, in turn, behave rather similarly to observed stock market volatilities but without any ghost effects. The author demonstrates how an alternative credit-based “fear gauge,” comparable to the CBOE VIX but emanating from the credit market, can be constructed using the credit-implied volatilities. He calls this implied volatility index the Credit-Implied Volatility Index (CIVX). Finally, a plot of the entire term structure of implied volatilities demonstrates a distinct maturity volatility skew.

Stock Prices and Stock Return Volatilities Implied by the Credit Market

In this paper we compare equity- and credit investors’ opinions on the price formation in the equity market. More exactly, we invert the CreditGrades model in order to back out credit-implied stock prices and stock return volatilities from credit default swap spreads for the firms in the DJIA index. The creditimplied stock prices often deviate significantly from actual stock prices over the longer term. Meanwhile, their day-to-day movements are significantly correlated with actual stock returns for most firms in the DJIA index. In an attempt to demonstrate potential applications of credit-implied stock prices we construct simple “capital structure arbitrage” trading strategies based on past credit-implied prices. Our strategies only require the buying and selling of stocks and differ from traditional cross-capital structure strategies by being suitable for retail investors and other investors without access to the credit derivatives market. The credit-implied volatilities, in turn, behave rather similarly to observed stock market volatilities but without any ghost effects. We demonstrate how an alternative credit-based “fear gauge”, comparable to the VIX index but emanating from the credit market, can be constructed using the credit-implied volatilities. We call this implied volatility index the Credit-Implied Volatility Index (CIVX) index. Finally, a plot of the entire term-structure of implied volatilities demonstrates a distinct maturity volatility skew.

The digital uncanny and ghost effects

This essay argues that the digital uncanny borrows and remediates three features of the Freudian Uncanny: an adherence to realist aesthetics; the structural repetition of images, situations and responses; and how surveillance undermines the features used to describe feelings of omnipotence and paranoia. By recycling these features, each artist binds realism, repetition and the uncertainty of power to the uncanny itself, leaving us only with their indeterminacy. Such uncertainties strip the body of its positioning as a locus of sensation, perception, and recollection, which in turn strips thought of its presuppositions, like the assumption that it is solely a human faculty. By uncoupling bodies and thinking from forms of representation – bodily images and images of thought – body and thought are themselves rendered indeterminate, ungrounded and uncanny. My goal is to examine how these interactive installations transform subjectivity and our visceral sense of embodiment into an act of mediation.

A spatially compact source designature filter

Source arrays are usually tuned for optimum primary-to-bubble ratio of the output. In addition, they may also be designed to mitigate source ghost effects, but such configurations introduce directivity effects as the generated downgoing wavefield varies with the source angles. We have investigated a practical source signature deconvolution operator, valid for any marine source array, which is able to remove source ghosts, residual bubble, and directivity effects from seismic data. The designature operator was designed to be a small wavenumber approximation of the inverse of the far-field signature of a source array, which involved the array geometry, the notional source signatures, and the firing synchronization of the sources. We have found that such an approximation leads to the design of spatially compact source designature (CSD) filters able to correct for shot-to-shot perturbations of the sources’ output and reduced their smearing due to the limited spatial aperture of the filters. They also had the potential to account for some source directivity and source ghost effects when applied to common receiver gathers. Our method was then further studied for a particular synchronized multilevel source array and azimuthal variations were neglected. First, tests on synthetic data were performed and the benefits and limitations of the approach were analyzed. Second, the method was tested on a field data set under further approximations that simplified the processing flow (1D earth and average notionals) and which enabled the direct application to common shot gathers. Our results have determined that the expected small — but nevertheless observable — improvements of source designature even at the target level improved event continuity, dephasing, and sharpening of the wavelet. Additionally, the CSD filter was used in conjunction and compared with the current best-practice data processing techniques.

Least-squares migration — Data domain versus image domain using point spread functions

Conventional amplitude inversion assumes that the migrated image preserves relative-amplitude information. However, illumination effects caused by complex geologic settings, undersampled acquisition geometry, and limited recording aperture pose a challenge to even the most advanced imaging algorithms. In addition, standard depth-migration images can suffer from lack of resolution caused by wavelet stretch, attenuation, and suboptimal deghosting. Least-squares migration (LSM) can mitigate many of these problems and produce better resolved migration images suitable for AVO inversion. However, whether formulated in the data domain or the image domain, LSM is an inversion algorithm and is sensitive to inaccuracies in the source wavelet, velocity model, data preprocessing, and the propagator used. Practical considerations to mitigate these problems under nonideal conditions and cost-reduction strategies differ between the data- and image-domain formulations. The relative merits of each approach are evaluated by using example inversions for complex synthetic models, including free-surface ghost and attenuation effects. When a data-domain implementation of LSM is considered necessary, the image-domain implementation should be considered at the same time, especially when targeting localized reservoir targets under complex overburdens. Application of image-domain least-squares migration on a Gulf of Mexico field data set produces significant improvements in resolution and event continuity in the subsalt target region.

Speculating on Superstition: Evidence from Housing Transactions in Hungry Ghost Months in Singapore

This paper aims to study the behavior of superstitious and non-superstitious investors surrounding the superstition that buying or selling during the Hungry Ghost month (typically August) will be inauspicious. We find that superstitious Chinese homebuyers pay 1.41% lower on average per square meter price for houses bought in the Hungry Ghost month than houses bought outside the Hungry Ghost month. We find that older Chinese, aged above 40 years who are more likely to be superstitious, pay a lower price relative to younger Chinese. On the other hand, the younger Chinese investors, who are more likely to be non-superstitious, speculate on the Hungry Ghost effects and buy cheaper. However, their investment strategies of timing buy-and-sale activities around the Hungry Ghost month do not yield significant abnormal returns.

Motion-compensated frame interpolation with weighted motion estimation and hierarchical vector refinement

Large amounts of data have been gathered by techniques such as mobile devices, remote sensing and cameras. With the rapid development of high-definition digital TV and multimedia information systems, motion-compensated frame interpolation (MCFI) has become a widely used tactic for frame rate up-conversion (FRUC) to improve the visual property of video. In this paper, we propose a novel MCFI algorithm based on weighted motion estimation (Weighted ME), motion vector (MV) segmentation, and hierarchical vector refinement. We first present an MV clustering based on the Weighted ME to obtain more accurate MVs and partition a frame into moving areas and background. To capture scene changes, we then apply a hierarchical vector refinement scheme to the moving areas that consists of three steps: pre-screening, reclassification, and smoothing. In this scheme, we use an overlapped block ME (OBME) method that uses multi-candidate pre-screening to discover unreliable MVs and protect the moving area edge structures from being damaged. We then employ the bidirectional prediction difference (BPD) to identify outliers using strong correlation with adjacent blocks. Meanwhile, an adaptive vector median filter (AVMF) is adopted to refine the block size, which can effectively smooth blocking artifacts and ghost effects. Experiments show the algorithm achieves a high image quality both subjectively and objectively. In particular, it has a good adaptability in video sequences with fast motion and complex backgrounds.

Deghosting of over/under towed-streamer seismic data with wavefield extrapolation

SUMMARY In marine seismic acquisition, ghost effect due to the strong reflection of the sea surface causes serious notch trap in the spectrum. Ghost effect can be reduced by over/under towed streamer acquisition. Howerver, most of deghosting technology for over/under streamer acquisition is based on seismic kinematics method, which cannot effectively solve the ghost wave interference and brings incomplete ghost suppression and distortion of the effective signal. In this paper, we propose a new deghosting method for over/under streamer acquisiton based on analytical fk-domain seismic wavefield extrapolation characterized by high computing efficiency. Cases studies of synthetic and real seismic datasets demonstrate that our seismic wavefield extrapolation based on Fourier transform ensures the consistency of the seismic amplitude and phase of over/under streamer seismic data and significantly eliminates the amplitude and phase error of far offset especially for the long streamer condition, which helps to decouple the real wave and the ghost wave and fill notch effect in the spectrum.

Blow up criterion for the 3D ghost effect system

In this paper, we establish a blow up criterion for strong solutions to the three dimensional ghost effect system.

Efficient Image Stitching of Continuous Image Sequence With Image and Seam Selections

This paper presents an efficient image stitching algorithm with better image quality and less processing time for online stitching of a continuous image sequence. Stitching many frames with similar scenes is time-consuming and easily generates inconsistency in the overlap region between frames. Instead of stitching every captured frame, only the dominant frames with significant visual content dissimilar to that in the previously stitched result are worthy of being stitched and can contribute much new information. Although the nondominant frames are not included in the mosaicked image, their homography matrix with respect to the mosaicked image will be roughly evaluated to localize the camera view on the mosaicked image as the region of stitching interest. A particle filter with partitioned sampling is utilized to categorize the stitching label and estimate the homography matrix. Moreover, to substantially increase the quality of offline image mosaicking, a seam planning algorithm is designed to eliminate the unclear ghost effect in the overlap region between dominant frames. The aim is to maximally preserve the visual content while eliminating inconsistencies in the overlap region. The proposed stitching algorithm has been verified in several online and offline experiments to present the efficiency of the overall system.

An Approach to Raspberry Pi Synchronization in a Multimedia Projection System for Applications in Presentation of Historical and Cultural Heritage

This paper discusses an implementation of a multimedia projection system with two synchronized video sources, based on the Raspberry Pi single board computer systems. The system is primarily intended for various projections in presentation of historical and cultural heritage, although it can be used for many other related purposes. The considered multimedia system has two projection surfaces - a horizontal projection plane and a 45° inclined special glass projection plane which creates the hologramlike Pepper’s Ghost effect. Each plane displays a separate high-definition video obtained from the corresponding Raspberry Pi. Synchronization of presentations is achieved using cu stom connection throu gh the general purpose input/output (GPIO) connector of the Raspberry Pi and the wiringPi interface library. As valuable aspects of the system, we can point out the following. From the practical point of view, the system has low cost due to the use of Rasp berry Pis. Generation of a holograp hic effect, as well as larger flexibility in creating the contents of the presentations due to the two projection surfaces, are additional attractive features.

On the Boltzmann gas mixture equation: Linking the kinetic and fluid regimes

This paper aims at developing a new connection between the Boltzmann equation and the Navier–Stokes equation. Specifically the paper deals with the derivation of the macroscopic equations from asymptotic limits of the Boltzmann equation for a binary gas mixture of hard-sphere gases. By extending the methodology of the single-component gases case and by employing different time and space scalings, we show that it is possible to recover, under suitable technical assumptions, various fluid dynamics equations like the incompressible linearized and nonlinear Navier–Stokes equations, the incompressible linearized and nonlinear Euler equations. The novelty of this paper is the method that we propose, which differs from the Hilbert and Chapman–Enskog expansions. Future research directions are also discussed in the last section of the paper with special attention at the different scalings that can be employed in order to obtain equations presenting a ghost effect.

Two-velocity hydrodynamics in fluid mechanics: Part I Well posedness for zero Mach number systems

In this paper we prove global in time existence of weak solutions to zero Mach number systems arising in fluid mechanics with periodic boundary conditions. Relaxing a certain algebraic constraint between the viscosity and the conductivity introduced in [6] gives a more complete answer to an open question formulated in [23]. We introduce a new mathematical entropy which clearly shows existence of two-velocity hydrodynamics with a fixed mixture ratio. As an application of our result we first discuss a model of gaseous mixture extending the results of [10] to the global weak solutions framework. Second, we present the ghost effect system studied by C.D. Levermore, W. Sun and K. Trivisa [20] and discuss a contribution of the density-dependent heat-conductivity coefficient to the issue of existence of weak solutions.

3-D imaging using row-column-addressed arrays with integrated apodization - part i: apodization design and line element beamforming.

This paper investigates the effect of transducerintegrated apodization in row-column-addressed arrays and presents a beamforming approach specific for such arrays. Row-column addressing 2-D arrays greatly reduces the number of active channels needed to acquire a 3-D volume. A disadvantage of row-column-addressed arrays is an apparent ghost effect in the point spread function caused by edge waves. This paper investigates the origin of the edge waves and the effect of introducing an integrated apodization to reduce the ghost echoes. The performance of a λ/2-pitch 5-MHz 128 + 128 row-column-addressed array with different apodizations is simulated. A Hann apodization is shown to decrease imaging performance away from the center axis of the array because of a decrease in main lobe amplitude. Instead, a static roll-off apodization region located at the ends of the line elements is proposed. In simulations, the peak ghost echo intensity of a scatterer at (x,y, z) = (8, 3, 30) mm was decreased by 43 dB by integrating roll-off apodization into the array. The main lobe was unaffected by the apodization. Simulations of a 3-mm-diameter anechoic blood vessel at 30 mm depth showed that applying the transducer-integrated apodization increased the apparent diameter of the vessel from 2.0 mm to 2.4 mm, corresponding to an increase from 67% to 80% of the true vessel diameter. The line element beamforming approach is shown to be essential for achieving correct time-of-flight calculations, and hence avoid geometrical distortions. In Part II of this work, experimental results from a capacitive micromachined ultrasonic transducer with integrated roll-off apodization are given to validate the effect of integrating apodization into the line elements.

Compensating for source and receiver ghost effects in full waveform inversion and reverse time migration for marine streamer data

In conventional marine seismic surveys, due to the time-delayed reflections from the sea surface on both source and receiver sides, ghosts present in recorded seismograms and lead to both phase and spectrum distortions (especially near certain frequency notches). To achieve a high-quality broad-band image/velocity model with conventional reverse time migration (RTM)/full waveform inversion (FWI) that adopts a synthetic zero-phase source wavelet and absorbing surface condition during wavefield modelling, marine seismic data have to be pre-processed to remove ghost effects. However, seismic deghosting is not a trivial task. Instead of employing an external deghosting process, we propose a strategy to compensate for ghost effects during FWI and RTM, which consists of two parts: first, to address phase distortions due to ghost effects by means of obtaining an accurate source wavelet estimation and adopting an appropriate surface boundary condition in both forward and backward wave propagation to appropriately generate ghosts; secondly, to build a compensation operator in the adjoint state computation to mitigate spectrum distortions caused by dominant ghost effects. To demonstrate the success and robustness of the proposed strategy, we present both synthetic experiments and field examples, which suggest that this strategy can lead to successful applications of FWI/RTM directly on marine seismic data without an extra deghosting process.

자동노출제어장치 센서적용을 위한 스크린 프린팅 제작방식의 고흡수율 광도전체 특성평가

Abstract In diagnostic radiology, the use of automatic exposure control device is internationally recommended for diagnosis and optimization. However, if exposed to prolonged radiation is a complicated manufacturing process, there is a problem that occurs decrease of various performance overall brightness sensor, which is commercially available conventional. Therefore, in this study, absorption of X-ray is high, and I want to evaluate the AEC applicability of the sensor of the photoconductor-based production has an easy advantage. Experimental results confirms the possibility of fabrication of the sensor through an increase in the SNR, with the detection efficiency superior, accurate turn-off. In addition, it is confirmed that the experimental results of the transmittance and the latent image, Ghost effect by the light conductor does not appear, in the case of a photoconductor with the exception of the PbO, 80% - and it was confirmed good transmittance of 90%. Therefore, excellent mechanical stability and poor performance due to a change of the doping concentration than the existing products that have been put to practical use, the sensor easy photoconductor based, fabrication and can be applied as AEC sensor is expected.

True-amplitude vector-acoustic imaging: Application of Gaussian beams

Acoustic Gaussian beam migration is an attractive imaging method because it is flexible with input geometry, efficient, and accurate in imaging multipath arrivals. However, one of the hurdles that this method must overcome in production processing is its extension to use multimeasurement data, as recently allowed by novel acquisition technologies. This is inevitable when the compensation of the ghost effect is best corrected within a true-amplitude imaging process, a necessity for amplitude-variation-with-offset work. For this purpose, I introduced a novel formalism for vector-acoustic imaging, based on Green’s function theory, which can remove the ghost effect and produce amplitudes on reflectors that are proportional to the reflection coefficients. I established a theoretical framework with Gaussian beam representations of Green’s functions, including the weighted beam-stacking approach that reduced the cost of computation. I extended my formulas to use the steep-descent (i.e., stationary phase) approximation. Then, I explained the impact of this approximation on the illumination and the event continuity and sharpness. I also studied the special case of acoustic imaging corresponding to using single-measurement (i.e., pressure) data. I applied the derived formulations to realistic synthetic multisensor data (North Sea) using a research code of Gaussian beam migration. The numerical examples demonstrated that I can improve the illumination of the final images and obtain wide-bandwidth reflectivity maps.

Use of PDLC Film for Improving Visualization of Contents in Holographic Display Under Different Illumination Scenarios

Abstract Pepper's ghost effect has been used since its beginnings at the second half of XIX century to generate 3D projections of virtual people in real environments. Nowadays this effect is used by ‘holographic’ displays for the projection not only of virtual people but also of objects and even animations that can interact with real objects. Marketing and product presentations are some of the most used applications for these displays. Nevertheless, another interesting application is been explored recently: knowledge transfer for both industrial and educational purposes. Regardless the application there is a little problem with these displays: when they are used in a high-illuminated place the contents projected are lost. That is the motivation for this project, which seeks to evaluate the use of a PDLC film (that allows to control its transmittance) to minimize these problem. Action research methodology is being used as a guideline for planning and executing the actions required in the project. The results were satisfactory; achieving an improvement in the visualizations of the contents displayed using the PDLC film.