Acoustic Impedance Profile Research Articles

Acoustic Impedance Inversion from Seismic Imaging Profiles Using Self Attention U-Net

Seismic impedance inversion is a vital way of geological interpretation and reservoir investigation from a geophysical perspective. However, it is inevitably an ill-posed problem due to the noise or the band-limited characteristic of seismic data. Artificial neural network have been used to solve nonlinear inverse problems in recent years. This research obtained an acoustic impedance profile by feeding seismic profile and background impedance into a well-trained self-attention U-Net. The U-Net got convergence by appropriate iteration, and the output predicted the impedance profiles in the test. To value the quality of predicted profiles from different perspectives, e.g., correlation, regression, and similarity, we used four kinds of indexes. At the same time, our results were predicted by conventional methods (e.g., deconvolution with recursive inversion, and TV regularization) and a 1D neural network was calculated in contrast. Self-attention U-Net showed to be robust to noise and does not require prior knowledge. Furthermore, spatial continuity is also better than deconvolution, regularization, and 1D deep learning methods in contrast. The U-Net in this paper is a type of full convolutional neural network, so there are no limits to the shape of the input. Based on this, a large impedance profile can be predicted by U-Net, which is trained by a patchy training dataset. In addition, this paper applied the proposed method to the field data obtained by the Ceduna survey without any label. The predictions prove that this well-trained network could be generalized from synthetic data to field data.

Gas Hydrate Accumulation Related to Pockmarks and Faults in the Zhongjiannan Basin, South China Sea

The amplitude and coherence attributes of three-dimensional (3D) seismic data are used to confirm gas hydrate occurrence and to delineate its distribution in the Zhongjiannan basin, South China Sea. High amplitude anomalies (HAAs) are distributed above or below the regional base of gas hydrate stability zone (BGHSZ), which intersect with the bottom simulating reflectors (BSRs) or are interrupted by different types of pockmarks. The maximum amplitude attribute extracted along T1 (5.5 Ma) horizon is controlled by the widely distributed faults. The layer-bound polygonal faults (PFs) show networks of small normal faults, and the dominant orientations of PFs are similar or orthogonal to the regional tectonic faults, which provide the fluid migration pathways for gas and fluids to form HAAs. BSR shows the strong amplitude and continuous reflection where the faults or PFs can reach the BGHSZ without the influence of the pockmarks. Most of the pockmarks are related to the reactivation of faults and magmation, and some pockmarks are caused by the dissociation of gas hydrate. Around the matured pockmark, the BSR is discontinuous, and HAAs locally appear within the pockmarks. The inverted acoustic impedance profile shows obviously high values of HAAs except in pockmark zones. Partial HAAs occur above BGHSZ, and the continuity is interrupted by the pockmarks with only high values around the pockmarks. We propose that BSR, HAAs, pockmarks, and different types of faults are closely related to the occurrence and distribution of gas hydrates in the study area. This work allows us to understand the relationship between gas hydrate occurrence and accumulation with pockmarks, faults, and magmatic activities.

On the Possibility of Reflectionless Propagation of Plane Acoustic Waves in Continuously Stratified Media

The example of vertical propagation of acoustic plane waves in the atmosphere is used to establish that the reflectionless propagation of acoustic waves occurs only in continuously stratified media for which wave equations with variable pressure perturbation and vibrational velocity coefficients are reduced—via the same transformation for the same wave acoustic impedance profile, which is inversely proportional to the refractive index—to a wave comparison equation with constant coefficients. It is shown that the corresponding transformations of the wave equations are possible only for continuously stratified media with a constant wave acoustic impedance.

Suppression of reflected signals from substrate as clutters for cell measurements using acoustic impedance microscopy

Recently, a method for estimating three-dimensional acoustic impedance profiles in cultured cells and human dermal organs was proposed by interpreting the reflected ultrasonic signal based on a 1-D transmission line model for acoustic impedance microscopy (AIM). However, AIM has a disadvantage that reflected signals from cells overlap with that from a reference substrate. Additionally, the amplitudes of the reflected signals from the specimens are significantly weaker than that from the substrate. In this paper, we proposed a new method for separation of those signals based on a concept of clutter filter, which had been developed for a color Doppler method in medical ultrasonic imaging. The proposed filter using singular value decomposition (SVD) could separate original signals into desired signals such as those from the substrate and cells. Additionally, an effect from a tilt of the substrate was investigated in this study. Separability of the proposed filter was evaluated by two investigations. First one was to evaluate the separability by estimating a correlation coefficient between the filtered signal and signal reflected from a position only with the substrate. Second one was to compare a slope of the substrate estimated from the original signal with that estimated from the filtered signals from the substrate. The experimental results showed that the proposed filter could separate signals from the substrate, and the compensation of the tilt of the substrate could improve the performance of the proposed filter.

Acoustic impedance interpretation of cross-sectional human skin by using time and frequency domain deconvolution

In the human cheek skin assessment using an ultrasound microscope, deconvolution is the process to estimate the reflection coefficient that comes only from the skin without the interference of any other components. The conventional deconvolution method which is performed only in the frequency domain will lead to the instability of the reconstructed signal, especially on the low-frequency components of the signal, causing the generation of artifacts when the result is converted into the acoustic impedance distribution. In order to deal with this, this paper presents a deconvolution technique in both the time and frequency domain. The essential low-frequency components are determined by the time domain deconvolution, which is then combined with the high-frequency components from the conventional frequency domain deconvolution method, and the cross-sectional acoustic impedance profile along the depth direction has been successfully observed.

Estimating broad trend of acoustic impedance profile from observed seismic reflection data using first principles only

Abstract Estimation of broad features or the low-frequency part of acoustic impedance from conventional reflection data is an essential yet challenging step for quantitative interpretation of seismic data due to its band-limited nature. A missing low-frequency part leads to non-uniqueness in the solution as well as placing restrictions in recovering the absolute impedance values. The current industry practice fills this gap by assuming either an initial impedance model or statistical restrictions on such a model. Doing away with such assumptions but using only first principles (Zoeppritz's equations) and homogeneous layered earth model, we have formulated a set of linear equations that are then solved for an unknown reflection co-efficient using singular value decomposition (SVD) approach with time sampled seismic trace as the input data. The present work demonstrates the effectiveness of reconstructing a broad and smooth impedance profile from first principles and even from acquired seismic reflection data. It also illustrates the method's success with real data, while determining in one go the unknown scale factor linking the true and the relative seismic amplitudes, and the smallest singular value to be retained in the solution from only the knowledge of the average value of the acoustic impedance over the depth range in question. Thus, the salient feature of this work is the ability to reconstruct an approximate impedance profile from field data without the aid of an initial model or statistical assumption on the reflectivity series. This approximate impedance profile can serve as a reliable initial input for more refined inversion or geologic interpretation.

Three-dimensional acoustic impedance mapping of cultured biological cells

The acoustic microscope is a powerful tool for the observation of biological matters. Non-invasive in-situ observation can be performed without any staining process. Acoustic microscopy is contrasted by elastic parameters like sound speed and acoustic impedance. We have proposed an acoustic microscope that can acquire three-dimensional acoustic impedance profile. The technique was applied to cell-size observation. Glial cells were cultured on a 70 μm-thick polypropylene film substrate. A highly focused ultrasound beam was transmitted from the rear side of the substrate, and the reflection was received by the same transducer. An acoustic pulse, its spectrum spreading briefly 100 through 450 MHz, was transmitted. By analyzing the internal reflections in the cell, the distribution of characteristic acoustic impedance along the beam direction was determined. Three-dimensional acoustic impedance mapping was realized by scanning the transducer, exhibiting the intra-cellular structure including nucleus and cytoskeleton.

Reaction assessment of cultured breast cancer cells exposed to anticancer agents using microscale acoustic impedance profile

The mechanical properties of living cells are known to be associated with disease states and cell function. In this study, acoustic impedance microscopy using a sapphire lens transducer with a center frequency of 320 MHz was employed to characterize the elasticity of the C127I cell line against an anticancer drug, nimustine hydrochloride (ACNU), and an anticancer agent, betulinic acid (BA). Confocal laser scanning microscopy was also used to investigate the drug affecting actin filaments, the nucleus, and mitochondria structures. Breast cancer cells were found to have significantly lower acoustic impedance after treatment with ACNU and BA than intact cells. Confocal images showed a significant difference in the localization of actin filaments and mitochondria structures, which suggested a difference in cell elasticity. An important insight emerging from this work is that the acoustic impedance of cells may potentially serve as a useful biomarker for anticancer drug efficacy tests, as diseases such as cancer have their own particular mechanical properties.

Broadband anomalous reflection caused by unsymmetrical specific acoustic impedance in phononic crystals

We investigate through numerical simulation the anomalous reflection (AR) of acoustic waves with perfect phononic crystals (PCs). Broadband AR is observed in a wide angle for the oblique incidence. The AR is due to the unsymmetrical specific acoustic impedance (SAI) profile along the surface, which is caused by the high frequency incidence. The findings in this paper complement the theories for the AR of acoustic waves with PCs, and may find applications in acoustic engineerings.

Transdimensional seismic inversion using the reversible jump Hamiltonian Monte Carlo algorithm

Prestack or angle stack gathers are inverted to estimate pseudologs at every surface location for building reservoir models. Recently, several methods have been proposed to increase the resolution of the inverted models. All of these methods, however, require that the total number of model parameters be fixed a priori. We have investigated an alternate approach in which we allow the data themselves to choose model parameterization. In other words, in addition to the layer properties, the number of layers is also treated as a variable in our formulation. Such transdimensional inverse problems are generally solved by using the reversible jump Markov chain Monte Carlo (RJMCMC) approach, which is a tool for model exploration and uncertainty quantification. This method, however, has very low acceptance. We have developed a two-step method by combining RJMCMC with a fixed-dimensional MCMC called Hamiltonian Monte Carlo, which makes use of gradient information to take large steps. Acceptance probability for such a transition is also derived. We call this new method “reversible jump Hamiltonian Monte Carlo (RJHMC).” We have applied this technique to poststack acoustic impedance inversion and to prestack (angle stack) AVA inversion for estimating acoustic and shear impedance profiles. We have determined that the marginal posteriors estimated by RJMCMC and RJHMC are in good agreement. Our results demonstrate that RJHMC converges faster than RJMCMC, and it therefore can be a practical tool for inverting seismic data when the gradient can be computed efficiently.

Hybridization and regularization schemes applied to identify rough acoustic impedance profiles in slender structures with noisy data.

The modified sequential algebraic algorithm (MSAA) is a routine developed to solve the longitudinal acoustic wave propagation problem in inhomogeneous media. This method accurately predicts the echo generated by the inhomogeneities, particularly when the acoustic impedance variation profile in the damaged part of the structure is non-smooth. Used for solving the inverse problem by a stochastic optimization approach, MSAA efficiently identifies rough profiles of impedance with low noise level in the input data. As noise level increases, the inverse problem turns out to be "ill-posed" and often yields inappropriate solutions. The purpose of this paper is to apply a regularization scheme and to use a hybrid optimization strategy to reduce the error in the damage estimation. In the numerical examples, 40 parameters are successfully identified for a signal to noise ratio of 20 dB. For all tested damage profiles, the regularization and hybridization procedures decreased the maximum absolute error to levels lower than 4%, and for the roughest impedance profile, the mean squared error was reduced by more than one order of magnitude and the error propagation was avoided. In an experimental validation, a pulse-echo essay was successfully conducted with the recovery of a damage with 264 parameters.

Mutual interpretation between B-mode image and cross-sectional acoustic microscopy

Acoustic microscopy is a two-dimensional profile of an acoustic parameter such as sound speed and characteristic acoustic impedance. It may be useful to understand how practically important B-mode image looks depending on cross-sectional spatial distribution of acoustic properties. In the presentation, it will be exhibited that B-mode echo-graph can be briefly reproduced from acoustic impedance profile observed by acoustic microscope by a similar process to the time domain reflectometry (TDR), with some simple assumptions. As an example, the acoustic impedance profile of a rat cerebellar tissue was acquired by acoustic impedance microscope that was developed in our lab. The B-mode image reproduced by calculation was compared with an actually acquired B-mode image. A good agreement between these two images was seen. On the other hand, a B-mode profile may be interpreted into cross-sectional distribution of acoustic profile. As it is attributed to inverse problem, several assumptions may be required. In the calculation, strait acoustic beam and no attenuation were assumed. In addition, the B-mode profile with RF waveforms was assumed to be available. In the presentation, it will be exhibited that cross-sectional acoustic impedance profile of a shallow region of human skin can be reproduced from non-invasive B-mode scan.

Feasibility of approximate broadband estimation of acoustic impedance profile from first principles and band-limited reflection data

Because seismic reflection data are band limited, acoustic impedance profiles derived from them are nonunique. The conventional inversion methods counter the nonuniqueness either by stabilizing the answer with respect to an initial model or by imposing mathematical constraints such as sparsity of the reflection coefficients. By making a nominal assumption of an earth model locally consisting of a stack of homogeneous and horizontal layers, we have formulated a set of linear equations in which the reflection coefficients are the unknowns and the recursively integrated seismic trace constitute the data. Drawing only on first principles, the Zoeppritz equation in this case, the approach makes a frontal assault on the problem of reconstructing reflection coefficients from band-limited data. The local layer-cake assumption and the strategy of seeking a singular value decomposition solution of the linear equations counter the nonuniqueness, provided that the objective is to reconstruct a smooth version of the impedance profile that includes only its crude structures. Tests on synthetic data generated from elementary models and from measured logs of acoustic impedance demonstrated the efficacy of the method, even when a significant amount of noise was added to the data. The emergence of consistent estimates of impedance, approximating the original impedance, from synthetic data generated for several frequency bands has inspired our confidence in the method. The other attractive outputs of the method are as follows: (1) an accurate estimate of the impedance mean, (2) an accurate reconstruction of the direct-current (DC) frequency of the reflectivity, and (3) an acceptable reconstruction of the broad outline of the original impedance profile. These outputs can serve as constraints for either more refined inversions or geologic interpretations. Beginning from the restriction of band-limited data, we have devised a method that neither requires a starting input model nor imposes mathematical constraints on the earth reflectivity and still yielded significant and relevant geologic information.

A modified sequential algebraic algorithm applied to identify rough acoustic impedance profiles in slender structures.

This paper develops and examines a modified technique for identifying damage in slender structures. An algorithm, called modified sequential algebraic algorithm, is presented to solve the longitudinal acoustic wave propagation problem in inhomogeneous media. This method accurately predicts the echo generated by the inhomogeneities when the acoustic impedance variation profile in the damaged part of the structure is non-smooth. For these cases, the available algorithms fail to provide the actual regressive wave component. In the following, a stochastic optimization scheme, the differential evolution method, is applied to solve the inverse problem. Numerical examples with smooth and non-smooth impedance profiles are considered. It is shown that, for smooth profiles, both the available techniques and the modified algorithm succeed in identifying the actual damage. Nevertheless, in situations where a rough profile is to be reconstructed, only the modified algorithm succeeds. The technique is found to be robust with respect to additive noise in the signals.

Multiscale seismic reflectivity of shallow thermoclines

AbstractSeismic oceanography is coming of age as an established technique of observation of the thermohaline structure of the ocean. The present paper deals with the seismic reflectivity of the Armorican Shelf seasonal thermocline, west of France, based on two seismic experiments performed with a sparker source. The peak frequency was 500 Hz for the ASPEX experiment, where the thermocline was located at 27 m water depth, and reduced to 400 Hz associated to a higher source level for the IFOSISMO experiment, where the thermocline was 12 m deeper. Despite these settings, only the first experiment could clearly highlight the thermocline reflector, providing the first seismic observation of a shallow oceanic structure. To better understand the limitation of high‐resolution seismic devices in detecting weak oceanic features, we develop a wavelet‐based seismic analysis and consider, as a first approximation, a simple thermocline modeled by a Gauss error function, allowing an analytical expression for the associated seismic reflectivity. We show that the acoustic impedance profile of the thermocline is mainly controlled by a sound velocity proportional to the temperature. We show that the seismic reflectivity is controlled by the reflection coefficient of the large‐scale structure of the thermocline and by an attenuation factor which depends on the ratio between the seismic wavelength and the characteristic size of the thermocline. Depending on this ratio, the strength of the thermocline‐related reflection may be too weak to be detected by seismic measurement.

Characteristics of bottom-simulating reflectors for Hydrate-filled fractured sediments in Krishna–Godavari basin, eastern Indian margin

The bottom-simulating reflector (BSR) is weak and patchy on the seismic section in the Krishna–Godavari basin, eastern Indian margin, where massive gas-hydrates have been recovered at Site 10 of the Indian National Gas-hydrates Program Expedition 01 (NGHP-01). The depth of the BSR near this site is around 160 m below the sea floor (mbsf). The average reflection coefficient from the BSR is −0.06, significantly smaller than the common global values of −0.1 to −0.2. The BSR shows a strong lateral variation in amplitudes along the seismic line due to the presence of faults. The methane solubility is modeled using a theoretical model of the gas-hydrates system, and methane concentrations from the pressure core show that the distribution of free gas below BSR is not uniform. A combination of synthetic seismogram analysis and rock physics modeling leads to the conclusion that weak and patchy BSRs are primarily caused by lateral discontinuities induced by the gas-filled fractures below BSRs. The free gas zone is thin and it shows segmented characteristics on the seismic section and acoustic impedance profile that we inverted. Fault zones increase the permeability and therefore trap gas in associated fractures that can scatter seismic energy and create low velocity zones.

Multiresolution seismic data fusion with a generalized wavelet-based method to derive subseabed acoustic properties

In the context of multiscale seismic analysis of complex reflectors, that takes benefit from broad-band frequency range considerations, we perform a wavelet-based method to merge multiresolution seismic sources based on generalized Levy-alpha stable functions. The frequency bandwidth limitation of individual seismic sources induces distortions in wavelet responses (WRs), and we show that Gaussian fractional derivative functions are optimal wavelets to fully correct for these distortions in the merged frequency range. The efficiency of the method is also based on a new wavelet parametrization, that is the breadth of the wavelet, where the dominant dilation is adapted to the wavelet formalism. As a first demonstration to merge multiresolution seismic sources, we perform the source-correction with the high and very high resolution seismic sources of the SYSIF deep-towed device and we show that both can now be perfectly merged into an equivalent seismic source with a broad-band frequency bandwidth (220-2200 Hz). Taking advantage of this new multiresolution seismic data fusion, the potential of the generalized wavelet-based method allows reconstructing the acoustic impedance profile of the subseabed, based on the inverse wavelet transform properties extended to the source-corrected WR. We highlight that the fusion of seismic sources improves the resolution of the impedance profile and that the density structure of the subseabed can be assessed assuming spatially homogeneous large scale features of the subseabed physical properties.

Abu Roash G dolomite reservoir characterization using seismic inversion technique, Horus field, Western Desert, Egypt

The main objective of this paper was the characterization of the reservoir (Abu Roash G dolomite) in terms of acoustic impedance from surface seismic data complemented by available well logs. To reach our target, a two-step procedure was followed: first, identification of the reservoir signatures using synthetic seismogram using Strata program in Hampson–Russell software and second, applying inversion technique to the post-stack seismic data using Strata program in Hampson–Russell software to obtain acoustic impedance profiles and maps. This procedure was applied to 12 3D seismic lines (six cross-lines, and six in-lines) from Horus field in Western Desert in Egypt after converting them from analog state to SEGY format by vectorization. Five wells had been used in this study. The outcome of this paper is an improved subsurface image of seismic data and achieving the reservoir characterization in a good way.

Reconstruction of the acoustic impedance profile in a plate using an inverse spectral procedure

An inverse spectral procedure was applied to reconstruct the acoustic impedance profile along the thickness direction of a plate using its thickness resonance frequencies, density and thickness. For a successful reconstruction, the material-property profile must be symmetric about the mid-plane of the plate. Several cases of numerical simulations, including plates with a few layers and with a high number of layers are described. The calculated resonance frequencies were used to reconstruct the acoustic impedance profile, a process that was successful for all cases. We assume that a plate with a high number of layers, each with a different but constant acoustic impedance, simulates a plate with a smoothly varying acoustic impedance profile. It can be concluded that such a plate, which generates small, virtually undetectable, internally reflected waves, can also be reconstructed. In the special case of a plate of unknown thickness and unknown but constant density, the method is still useful, because a relative variation of the material property can be reconstructed using only the resonance frequencies. An experiment using a resonance-mode electromagnetic acoustic transducer (resonance-mode EMAT) is also described. EMAT is a non-contact ultrasonic method that can measure thickness resonance frequencies, making it appropriate for this method. Some examples of applications are measurement of the temperature profile inside a rolled metal sheet, measurement of a clad metal plate, and monitoring of a metal casting.

Parâmetros físicos de sedimentos marinhos superficiais da região costeira de Caravelas, Sul da Bahia

Este trabalho combina informacoes obtidas por testemunhos de sondagem com dados adquiridos por perfilagem geofisica a fim de verificar a influencia dos parâmetros geologicos e sedimentologicos na velocidade de ondas P em sedimentos marinhos superficiais. Dados de velocidade da onda compressional (Vp), densidade gama, impedância acustica e susceptibilidade magnetica foram correlacionados com dados geologicos de quatro testemunhos coletados na zona costeira da cidade de Caravelas, estado da Bahia. As propriedades geofisicas foram obtidas utilizando como sistema de medicao o perfilador multisensor de testemunhos (MultiSensor Core Logger - MSCL). Os testemunhos foram descritos segundo a geologia, cor e grau de compactacao. Oito tipos distintos de sedimentos foram observados: conchas, areia grossa a muito grossa, areia media, areia muito fina a fina, lama arenosa, lama compacta, lama fluida e lama muito fluida. Os resultados mostram que, de maneira geral, os maiores valores de velocidade e densidade, inversamente proporcionais aos de susceptibilidade magnifica, estao associados aos sedimentos de maior granulometria. Os valores de Vp para areia muito grossa e conchas mostrou-se erratico devido a falta de compactacao desses materiais. Os graficos de impedância acustica e do coeficiente de reflexao facilitaram a identificacao de interfaces e apresentaram coerencia em relacao aos perfis de velocidade e de densidade. Medicoes de granulometria foram realizadas na secao de lama arenosa do testemunho JP-112, para ratificar a relacao da variabilidade dos parâmetros fisicos com a classificacao granulometrica utilizada para a caracterizacao dos quatro testemunhos.