Simultaneous Sources Research Articles

Deghosting by echo‐deblending

ABSTRACTA marine source generates both a direct wavefield and a ghost wavefield. This is caused by the strong surface reflectivity, resulting in a blended source array, the blending process being natural. The two unblended response wavefields correspond to the real source at the actual location below the water level and to the ghost source at the mirrored location above the water level. As a consequence, deghosting becomes deblending (‘echo‐deblending’) and can be carried out with a deblending algorithm. In this paper we present source deghosting by an iterative deblending algorithm that properly includes the angle dependence of the ghost: It represents a closed‐loop, non‐causal solution. The proposed echo‐deblending algorithm is also applied to the detector deghosting problem. The detector cable may be slanted, and shot records may be generated by blended source arrays, the blending being created by simultaneous sources. Similar to surface‐related multiple elimination the method is independent of the complexity of the subsurface; only what happens at and near the surface is relevant. This means that the actual sea state may cause the reflection coefficient to become frequency dependent, and the water velocity may not be constant due to temporal and lateral variations in the pressure, temperature, and salinity. As a consequence, we propose that estimation of the actual ghost model should be part of the echo‐deblending algorithm. This is particularly true for source deghosting, where interaction of the source wavefield with the surface may be far from linear. The echo‐deblending theory also shows how multi‐level source acquisition and multi‐level streamer acquisition can be numerically simulated from standard acquisition data. The simulated multi‐level measurements increase the performance of the echo‐deblending process. The output of the echo‐deblending algorithm on the source side consists of two ghost‐free records: one generated by the real source at the actual location below the water level and one generated by the ghost source at the mirrored location above the water level. If we apply our algorithm at the detector side as well, we end up with four ghost‐free shot records. All these records are input to migration. Finally, we demonstrate that the proposed echo‐deblending algorithm is robust for background noise.

Segregating two simultaneous sounds in elevation using temporal envelope: Human psychophysics and a physiological model.

The ability to segregate simultaneous sound sources based on their spatial locations is an important aspect of auditory scene analysis. While the role of sound azimuth in segregation is well studied, the contribution of sound elevation remains unknown. Although previous studies in humans suggest that elevation cues alone are not sufficient to segregate simultaneous broadband sources, the current study demonstrates they can suffice. Listeners segregating a temporally modulated noise target from a simultaneous unmodulated noise distracter differing in elevation fall into two statistically distinct groups: one that identifies target direction accurately across a wide range of modulation frequencies (MF) and one that cannot identify target direction accurately and, on average, reports the opposite direction of the target for low MF. A non-spiking model of inferior colliculus neurons that process single-source elevation cues suggests that the performance of both listener groups at the population level can be accounted for by the balance of excitatory and inhibitory inputs in the model. These results establish the potential for broadband elevation cues to contribute to the computations underlying sound source segregation and suggest a potential mechanism underlying this contribution.

Separation and reconstruction of simultaneous source data via iterative rank reduction

We have developed a rank-reduction algorithm based on singular spectrum analysis (SSA) that is capable of suppressing the interferences generated by simultaneous source acquisition. We evaluated an inversion scheme that minimizes the misfit between predicted and observed blended data in [Formula: see text] domain subject to a low-rank constraint that is applied to data in the [Formula: see text] domain. In particular, we developed an iterative algorithm by adopting the projected gradient method with the SSA filter acting as the projection operator. This method entails extracting small patches of data from a common receiver gather and organizing the spatial data at a given monochromatic frequency into a Hankel matrix. For the ideal unblended data, Hankel matrices extracted from the data are of low rank. The incoherent interferences in common-receiver domain caused by simultaneously fired shots increase the rank of the aforementioned Hankel matrices. Therefore, rank-reduction filtering is an effective way to annihilate source interferences while preserving the unblended signal. Through tests with synthetic examples, we found that the interference can be effectively suppressed by the proposed method. In addition, we found that the proposed algorithm can be modified to simultaneously cope with deblending and data recovery. A real survey acquired in the Gulf of Mexico was used to mimic a simultaneous-source acquisition with missing shot locations. The algorithm was able to recover the missing shot gathers from the blended acquisition with an improvement of the signal quality of approximately 12 dB.

Broadband implementation of coprime linear microphone arrays for direction of arrival estimation.

Coprime arrays represent a form of sparse sensing which can achieve narrow beams using relatively few elements, exceeding the spatial Nyquist sampling limit. The purpose of this paper is to expand on and experimentally validate coprime array theory in an acoustic implementation. Two nested sparse uniform linear subarrays with coprime number of elements ( M and N) each produce grating lobes that overlap with one another completely in just one direction. When the subarray outputs are combined it is possible to retain the shared beam while mostly canceling the other superfluous grating lobes. In this way a small number of microphones ( N+M-1) creates a narrow beam at higher frequencies, comparable to a densely populated uniform linear array of MN microphones. In this work beampatterns are simulated for a range of single frequencies, as well as bands of frequencies. Narrowband experimental beampatterns are shown to correspond with simulated results even at frequencies other than the arrays design frequency. Narrowband side lobe locations are shown to correspond to the theoretical values. Side lobes in the directional pattern are mitigated by increasing bandwidth of analyzed signals. Direction of arrival estimation is also implemented for two simultaneous noise sources in a free field condition.

Simultaneous Source Detection and Analysis Using a Zero-inflated Count Rate Model

This paper proposes a novel Bayesian technique that allows for simultaneous source detection and count rate analysis. The technique involves using priors, which include a finite probability that the source count rate is exactly zero. Such priors are called "zero-inflated." Solving the posterior distribution of a zero-inflated count rate model provides the probability that the sample contains a source and a probability distribution for the source count rate if the source exists, without the need to perform redundant computations. Sampling from zero-inflated distributions is straightforward and can be accomplished with easily accessible open source software. In addition, zero-inflated priors lead to finite posterior probabilities of "no source," which is an easy-to-understand and satisfying result.

Multiple Frequency Contrast Source Inversion Method for Vertical Electromagnetic Profiling: 2D Simulation Results and Analyses

A simultaneous multiple frequency contrast source inversion (CSI) method is applied to reconstructing hydrocarbon reservoir targets in a complex multilayered medium in two dimensions. It simulates the effects of a salt dome sedimentary formation in the context of reservoir monitoring. In this method, the stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) algorithm is applied as a fast solver for the 2D volume integral equation for the forward computation. The inversion technique with CSI combines the efficient FFT algorithm to speed up the matrix–vector multiplication and the stable convergence of the simultaneous multiple frequency CSI in the iteration process. As a result, this method is capable of making quantitative conductivity image reconstruction effectively for large-scale electromagnetic oil exploration problems, including the vertical electromagnetic profiling (VEP) survey investigated here. A number of numerical examples have been demonstrated to validate the effectiveness and capacity of the simultaneous multiple frequency CSI method for a limited array view in VEP.

Simultaneous optical flow and source estimation: Space–time discretization and preconditioning

We consider the simultaneous estimation of an optical flow field and an illumination source term in a movie sequence. The particular optical flow equation is obtained by assuming that the image intensity is a conserved quantity up to possible sources and sinks which represent varying illumination. We formulate this problem as an energy minimization problem and propose a space–time simultaneous discretization for the optimality system in saddle-point form. We investigate a preconditioning strategy that renders the discrete system well-conditioned uniformly in the discretization resolution. Numerical experiments complement the theory.

Impact of flash flood events on the distribution of organic pollutants in surface sediments from a Mediterranean coastal lagoon (Mar Menor, SE Spain).

The influence of flash flood events on the input and distribution of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorinated pesticides (OCPs) in surface sediments from the Mar Menor lagoon were characterized in this study. These contaminants were analyzed in surface water samples collected during two flash flood events in the main surface watercourse which flow into the Mar Menor lagoon. Surface sediments were sampled semiannually before and after flash flood events. The total input of PAHs, OCPs, and PCBs (sorbed + dissolved) during two flash flood events was estimated at 0.98, 1.32, and 0.34kg, respectively, the main input corresponding to p,p'-DDE (1.00kg). The distribution of organic contaminants in surface sediments was not homogeneous as a consequence of the presence of many simultaneous sources and different meteorological, hydrodynamic, and physicochemical conditions. As a consequence of flash flood events, p,p'-DDE concentrations in surface sediments increased significantly in the central and south zones of the lagoon. However, in the case of PCBs, a dilution effect was observed in the south zone after such events, reducing the environmental risk. These changes in the pollutant distribution persisted at least 1year later (autumn 2010), showing that the impact of flood events in the distribution of persistent organic contaminants in Mediterranean coastal lagoons is of relevance according to the ecological risk assessment carried out. The impact of these events should be also considered in other coastal systems, especially in semiarid and semiconfined areas.

Full waveform inversion in the frequency domain using direct iterative T-matrix methods

We present two direct iterative solutions to the nonlinear seismic waveform inversion problem that are based on volume integral equation methods for seismic forward modelling in the acoustic approximation. The solutions are presented in the frequency domain, where accurate inversion results can often be obtained using a relatively low number of frequency components. Our inverse scattering approach effectively replaces an ill-posed nonlinear inverse problem with a series of linear ill-posed inverse problems, for which there already exist efficient (regularized) solution methods. Both these solutions update the wavefield within the scattering domain after each iteration. The main difference is that the background medium Green functions are kept fixed in the first solution, but updated after each iteration in the second solution. This means that our solutions are very similar to the Born iterative (BI) and the distorted Born iterative (DBI) methods that are commonly used in acoustic and electromagnetic inverse scattering. However, we have eliminated the need to perform a full forward simulation (or to invert a huge matrix) at each iteration via the use of an iterative T-matrix method for fixed background media for the BI method and a variational T-matrix method for dynamic background media for the DBI method. The T-matrix (variation) is linearly related with the seismic wavefield data (residuals), but related with the unknown scattering potential model parameter (updates) in a non-linear manner, which is independent of the source-receiver configuration. This mathematical structure, which allows one to peel off the effects of the source-receiver configuration, is very attractive when dealing with multiple (simultaneous) sources, and is also compatible with the (future) use of renormalization methods for dealing with local minima problems. To illustrate the performance and potential of the two direct iterative methods for FWI, we performed a series of numerical experiments on synthetic seismic waveform data associated with a simple 2D model and the more complicated Marmousi model. The results of these numerical experiments suggest that the use of a fixed (e.g. smooth and ray-tracing friendly) background medium may be adequate for some applications with moderately large velocity contrasts, but the solution based on a dynamic (non-smooth and constantly updated) background medium will normally provide superiour inversion results; also in the case of low signal-to-noise ratios.

Lightweight multi-DOA tracking of mobile speech sources

Estimating the directions of arrival (DOAs) of multiple simultaneous mobile sound sources is an important step for various audio signal processing applications. In this contribution, we present an approach that improves upon our previous work that is now able to estimate the DOAs of multiple mobile speech sources, while being light in resources, both hardware-wise (only using three microphones) and software-wise. This approach takes advantage of the fact that simultaneous speech sources do not completely overlap each other. To evaluate the performance of this approach, a multi-DOA estimation evaluation system was developed based on a corpus collected from different acoustic scenarios named Acoustic Interactions for Robot Audition (AIRA).

Cortical representations sensitive to the number of perceived auditory objects emerge between 2 and 4 months of age: electrophysiological evidence.

Sound waves emitted by two or more simultaneous sources reach the ear as one complex waveform. Auditory scene analysis involves parsing a complex waveform into separate perceptual representations of the sound sources [Bregman, A. S. Auditory scene analysis: The perceptual organization of sounds. London: MIT Press, 1990]. Harmonicity provides an important cue for auditory scene analysis. Normally, harmonics at integer multiples of a fundamental frequency are perceived as one sound with a pitch corresponding to the fundamental frequency. However, when one harmonic in such a complex, pitch-evoking sound is sufficiently mistuned, that harmonic emerges from the complex tone and is perceived as a separate auditory object. Previous work has shown that the percept of two objects is indexed in both children and adults by the object-related negativity component of the ERP derived from EEG recordings [Alain, C., Arnott, S. T., & Picton, T. W. Bottom-up and top-down influences on auditory scene analysis: Evidence from event-related brain potentials. Journal of Experimental Psychology: Human Perception and Performance, 27, 1072-1089, 2001]. Here we examine the emergence of object-related responses to an 8% harmonic mistuning in infants between 2 and 12 months of age. Two-month-old infants showed no significant object-related response. However, in 4- to 12-month-old infants, a significant frontally positive component was present, and by 8-12 months, a significant frontocentral object-related negativity was present, similar to that seen in older children and adults. This is in accordance with previous research demonstrating that infants younger than 4 months of age do not integrate harmonic information to perceive pitch when the fundamental is missing [He, C., Hotson, L., & Trainor, L. J. Maturation of cortical mismatch mismatch responses to occasional pitch change in early infancy: Effects of presentation rate and magnitude of change. Neuropsychologia, 47, 218-229, 2009]. The results indicate that the ability to use harmonic information to segregate simultaneous sounds emerges at the cortical level between 2 and 4 months of age.

A hybrid algorithm based on s transform and affinity propagation clustering for separation of two simultaneously artificial partial discharge sources

This paper presents a hybrid algorithm for separation of two simultaneous partial discharge (PD) sources of oil-paper insulation based on S transform (ST) and affinity propagation clustering (APC). Similarities between PD pulses are acquired by comparisons of the corresponding ST-amplitude (STA) matrices, which are input of APC to realize the PD pulses separation and obtain two sub-groups of PD pulses having similar time-frequency characteristics. A classification-based model for separation results validation are developed using a support vector machine with particle swarm optimization (PSO-SVM) classifier and 27 phase-resolved partial discharge (PRPD) statistical features. Artificial defect models are made to simulate two PD sources simultaneously active. Several PD data of different two simultaneous PD sources are acquired in laboratory and adopted for algorithm testing. It is shown that ST computes very fast and is suitable for online PD applications. The separation results of PD data produced in laboratory are verified by the developed validation model, which demonstrate that ST combined with APC can effectively eliminate pulse-shaped noises (PSN) and separate pulses of two simultaneous PD sources. Comparisons with typical separation methods from the state of the art provide better separation performance of the proposed ST combined with APC algorithm for two simultaneous PD sources. The obtained results in this work provide a solid basis for the data mining technique that can be used to facilitate PD diagnosis of transformers.

Su1016 Risk Factors for Post-Operative Respiratory Failure in Liver Transplant Recipients

Rationale: Post-operative respiratory failure (PRF) is a common complication after liver transplant (LT). PRF leads to increased length of intensive care unit (ICU) and hospital stay and predisposes to increased morbidity in the post-operative period. Further investigation is needed to identify risk factors for PRF in LT recipients. Aim: To evaluate pre-operative cardiopulmonary testing, recipient, donor, and surgical variables and their utility in prediction of PRF after LT. Methods: Retrospective case-control study performed on LT recipients from 2010-2012. Post-operative course was reviewed to evaluate for cases of PRF, defined as failure to extubate before or unplanned re-intubation within 48 hours from completion of LT surgery. Pre transplant recipient demographic characteristics were recorded. Donor and surgical characteristics including: simultaneous kidney transplant, cytomegalovirus (CMV) status, gender, donor source (deceased or living), age, warm and cold ischemic times were assessed. Pre-transplant cardiopulmonary testing examined included: the presence or absence of heart failure, diastolic dysfunction, left ventricular ejection fraction, right ventricular systolic pressure, forced expiratory volume in one second to forced vital capacity ratio (FEV1/ FVC), forced vital capacity (FVC), total lung capacity (TLC), forced expiratory volume in one second ( FEV1), and diffusion limit of carbon monoxide (DLCO). Variables of interest were analyzed using univariate logistic regression with an end point of PRF. Factors deemed most significant (p < 0.25) in predicting PRF were included in a multivariate regression analysis to estimate adjusted odds ratios (OR) for each variable. Variables with p < 0.05 were considered significant predictors of PRF in the final model. Results: A total of 170 patients were identified. Of those, 23.7% experienced PRF. Significant predictors including pre-transplant MELD, pre-operative respiratory failure, FVC <80%, FEV1 <80%, TLC <80%, and deceased donor source from univariate logistic regression [Table 1] were entered into multivariate logistic regression. In the final model, pre-operative respiratory failure (OR= 161.48, p = 0.002) was found to be predictive of PRF, in a model that explained 26.3 to 41.7% of variance [Table 2].Conclusions: Pre-operative respiratory failure from any etiology was identified as a significant predictor of PRF after LT. Pre-LT echocardiogram and pulmonary function testing had no predictive value for PRF. These findings support the development of protocols to aggressively wean ventilatory support immediately prior to LT. Univariate Analysis: Post-Operative Respiratory Failure

Field-wide implementation of time and distance separated source techniques on a 3D OBC survey offshore Abu Dhabi, UAE

ADMA-OPCO undertook a large 3D-4C OBC (ocean bottom cable) survey over an oil and gas field offshore Abu Dhabi, UAE. The survey was designed to acquire a high-fold dataset having wide azimuth and long offset sampling. The survey utilized, for the first time, two simultaneous source techniques so-called DS3 (Distance Separated Simultaneous Shooting) and MSS (Managed Spread and Sources) to enhance survey productivity and minimize HSE exposure in the field. DS3 and MSS involve two source vessels operating simultaneously while maintaining predetermined separations among shots in time and space to produce records with minimal contamination of seismic interferences. Unlike land surveys, these two techniques had not previously been applied to an OBC survey. To ensure adequacy of the techniques, the acquisition started with 2D tests prior to full-field implementation. With DS3 and MSS, the 3D survey yielded remarkable enhancement of survey productivity as compared to conventional single source vessel configuration. DS3 and MSS along with proper temporal and spatial source vessel separations enable recorded data to be handled as if acquired by non-simultaneous source survey.

Experience a conflict-either consciously or not (commentary on Desender, Van Opstal, and Van den Bussche, 2014).

Experience a conflict-either consciously or not (commentary on Desender, Van Opstal, and Van den Bussche, 2014).

Deblending using a high-resolution radon transform in a common midpoint domain

The advantages of simultaneous sources acquisition are weakened by blended noise. Many conventional filtering methods are ineffective due to the existence of coherent blended noise in common shot gather (CSG). However, the coherent interference appears to be incoherent in a common midpoint (CMP) domain. In light of this characteristic, we propose a high-resolution radon transform based deblending approach. There are four steps for the implementation: (1) transform the original data from a CSG domain to a CMP domain; (2) apply the high-resolution radon transform to CMP gather to obtain the radon spectrum; (3) filter the radon spectrum with iterative threshold method; (4) transform the filtered data from the radon domain back to time spatial domain. The key step of the proposed method is to obtain the high-resolution radon spectrum to which the threshold filtering is applied. We give synthetic and field data examples to show the effectiveness of our approach.

Seismic imaging of simultaneous-source data using constrained least-squares reverse time migration

Simultaneous-source acquisition can help obtain better-sampled seismic data with a tremendously faster efficiency. However, the interference caused between simultaneous sources will cause strong artifacts in the migrated image. We propose to directly migrate the blended data without deblending. We treat the imaging for blended seismic data as a least-squares inversion problem, and use preconditioned conjugate gradient algorithm to iteratively solve it. The constraining operator is chosen as the structural smoothing operator, which helps to smooth the seismic image along the local structure. Compared with other available approaches, the proposed approach can obtain a true-amplitude and much cleaner image.

Simultaneous microseismic event localization and source mechanism determination

Microseismic monitoring has become a tool of choice for the development and optimization of oil and gas production from unconventional reservoirs. The primary objective of (micro) seismic monitoring includes localization of (micro) seismic events and characterization of their source mechanisms. Most seismic events are of a nonexplosive nature, and thus, there are waveform (polarity) differences among receivers. Specifically, double-couple sources represented a challenge for migration-based localization techniques. We developed and applied a new migration-type location technique combined with source mechanism inversion that allowed for constructive interference of signal in seismic waveforms. The procedure included constructing image functions by stacking the amplitudes with compensated polarity changes. The compensation weights were calculated by using moment tensor inversion. This method did not require any picking of arrivals at individual receivers, but it required receivers to be distributed in multiple azimuths and offsets. This made the technique suitable for surface or near-surface monitoring, in which a low signal-to-noise ratio (S/N) can be overcome by stacking. Furthermore, the advantage of this technique was that in addition to the position in time and space, we also determined the source mechanism. We determined with numerical tests that the proposed technique can be used for detection and location of events with S/Ns as low as 0.05 at individual (prestacked) receivers. Furthermore, we found that other source mechanism parameters such as magnitude, volumetric, or shear components of the source mechanism were not suitable for the location. Finally, we applied the proposed technique to a microseismic event of moment magnitude [Formula: see text] induced during the hydraulic fracturing treatment of a gas shale reservoir in North America.

Partially coherent phase imaging with simultaneous source recovery.

We propose a new method for phase retrieval that uses partially coherent illumination created by any arbitrary source shape in Köhler geometry. Using a stack of defocused intensity images, we recover not only the phase and amplitude of the sample, but also an estimate of the unknown source shape, which describes the spatial coherence of the illumination. Our algorithm uses a Kalman filtering approach which is fast, accurate and robust to noise. The method is experimentally simple and flexible, so should find use in optical, electron, X-ray and other phase imaging systems which employ partially coherent light. We provide an experimental demonstration in an optical microscope with various condenser apertures.

Projection imaging with directional electron and proton beams emitted from an ultrashort intense laser-driven thin foil target

Projection images of a metal mesh produced by directional MeV electron beam together with directional proton beam, emitted simultaneously from a thin foil target irradiated by an ultrashort intense laser, are recorded on an imaging plate for the electron imaging and on a CR-39 nuclear track detector for the proton imaging. The directional electron beam means the portion of the electron beam which is emitted along the same direction (i.e., target normal direction) as the proton beam. The mesh patterns are projected to each detector by the electron beam and the proton beam originated from tiny virtual sources of ~20 µm and ~10 µm diameters, respectively. Based on the observed quality and magnification of the projection images, we estimate sizes and locations of the virtual sources for both beams and characterize their directionalities. To carry out physical interpretation of the directional electron beam qualitatively, we perform 2D particle-in-cell simulation which reproduces a directional escaping electron component, together with a non-directional dragged-back electron component, the latter mainly contributes to building a sheath electric field for proton acceleration. The experimental and simulation results reveal various possible applications of the simultaneous, synchronized electron and proton sources to radiography and pump-probe measurements with temporal resolution of ~ps and spatial resolution of a few tens of µm.