Journal articles on the topic 'Impedance contrasts'
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Cao, D., W. B. Beydoun, S. C. Singh, and A. Tarantola. "A simultaneous inversion for background velocity and impedance maps." GEOPHYSICS 55, no. 4 (April 1990): 458–69. http://dx.doi.org/10.1190/1.1442855.
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Full‐waveform inversion of seismic reflection data is highly nonlinear because of the irregular form of the function measuring the misfit between the observed and the synthetic data. Since the nonlinearity results mainly from the parameters describing seismic velocities, an alternative to the full nonlinear inversion is to have an inversion method which remains nonlinear with respect to velocities but linear with respect to impedance contrasts. The traditional approach is to decouple the nonlinear and linear parts by first estimating the background velocity from traveltimes, using either traveltime inversion or velocity analysis, and then estimating impedance contrasts from waveforms, using either waveform inversion or conventional migration. A more sophisticated strategy is to obtain both the subsurface background velocities and impedance contrasts simultaneously by using a single least‐squares norm waveform‐fit criterion. The background velocity that adequately represents the gross features of the medium is parameterized using a sparse grid, whereas the impedance contrasts use a dense grid. For each updated velocity model, the impedance contrasts are computed using a linearized inversion algorithm. For a 1-D velocity background, it is very efficient to perform inversion in the f-k domain by using the WKBJ and Born approximations. The method performs well both with synthetic and field data.
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Morozov, Igor B. "Exact elastic P/SV impedance." GEOPHYSICS 75, no. 2 (March 2010): C7—C13. http://dx.doi.org/10.1190/1.3318268.
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Several extensions of the concept of acoustic impedance (AI) to oblique incidence exist and are known as elastic impedances (EI). These quantities are constructed by heuristic integrations of reflectivity series but still involve approximations and do not represent a unique medium property. Nevertheless, for unambiguous interpretation, it is desirable to have an EI that would (1) be a mechanical property of the medium and (2) yield exact reflection coefficients at all angles of incidence. Here, such a definition is given for P- and/or SV-wave propagation in an arbitrary isotropic medium. The exact elastic P/SV impedance is a matrix quantity and represents the differential operator relating the stress and strain boundary conditions. With the use of the matrix form of the reflectivity problem, no approximations are required for accurate modeling of reflection (P/P and SV/SV) and mode-conversion (P/SV and SV/P) coefficients at all angles and for any contrasts in elastic properties. The matrix EI can be computed from real well logs and inverted from ray-parameter-dependent seismic reflectivity. Known limiting cases of P- and S-wave acoustic impedances are accurately reproduced and the approach also allows the extension of the concept of impedance to an attenuative medium. The matrix impedance readily lends itself to inversion with uncertainties typical of the standard acoustic-impedance inversion problem.
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Kiyashchenko, Denis, René-Edouard Plessix, and Boris Kashtan. "Modified imaging principle: An alternative to preserved-amplitude least-squares wave-equation migration." GEOPHYSICS 72, no. 6 (November 2007): S221—S230. http://dx.doi.org/10.1190/1.2786867.
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Impedance contrast images can result from a least-squares migration or from a modified imaging principle. Theoretically, the two approaches should give similar results, but in practice they lead to different estimates of the impedance contrasts because of limited acquisition geometry, difficulty in computing exact weights for least-squares migration, and small contrast approximation. To analyze those differences, we compare the two approaches based on 2D synthetics. Forward modeling is either a finite-difference solver of the full acoustic wave equation or a one-way wave-equation solver that correctly models the amplitudes. The modified imaging principle provides better amplitude estimates of the impedance contrasts and does not suffer from the artifacts at-tributable to diving waves, which can be seen in two-way, least-squares migrated sections. However, because of the shot-based formulation, artifacts appear in the modified imaging principle results in shadow zones where energy is defocused. Those artifacts do not exist with the least-squares migration algorithm because all shots are processed simultane-ously.
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Cho, Yongchae, Richard L. Gibson Jr., and Dehan Zhu. "Quasi 3D transdimensional Markov-chain Monte Carlo for seismic impedance inversion and uncertainty analysis." Interpretation 6, no. 3 (August 1, 2018): T613—T624. http://dx.doi.org/10.1190/int-2017-0136.1.
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Accurate estimation of subsurface properties plays an important role in successful hydrocarbon exploration, and a variety of different types of inversion schemes are used to infer earth properties such as velocity or density by analyzing the surface seismic. The Markov-chain Monte Carlo (MCMC) stochastic approach is widely used to estimate subsurface properties. We have used a transdimensional form of MCMC, reversible jump MCMC (RJMCMC), to estimate seismic impedance, which allows the inference of the number of interfaces as well as the interface location and layer impedances. Estimating the uncertainty quantitatively is also very important when performing stochastic inversion. Therefore, the goal of this paper is to apply the transdimensional method to obtain a 3D seismic impedance model and to quantify uncertainty in impedance and interface locations. We also measured the speedup of the proposed algorithm by applying data and task parallelism. To demonstrate the performance and reliability of the proposed RJMCMC impedance inversion, we used seismic data from the E-segment of the Norne field in Norwegian Sea. The results of the quasi 3D transdimensional MCMC approach, which independently inverts data from each common-depth-point location, indicate high velocity contrasts near gas-oil contacts and high uncertainty in impedance near discontinuities. Also, the cross section of the impedance uncertainty volume helps to identify the location of a high-contrast boundary corresponding to the location of the possible gas reservoir. The proposed uncertainty measure can serve as an attribute to identify important reservoir features.
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Tobias, Steve. "Interpreters and near-field exploration: The role of leadership, culture, and organizational impedance contrasts." Interpretation 6, no. 2 (May 1, 2018): 5M—12M. http://dx.doi.org/10.1190/int-2018-0214-ps.1.
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Four years ago, several visionaries from SEG and AAPG collaborated to create Interpretation, a journal that serves the unique community of integrated interpretation. As the late R. Randy Ray wrote at the time, “It marks a historic recognition that geology and geophysics are intertwined at the core.” Indeed, this core community drives the exploration engine that powers the oil and gas industry through the multidisciplinary study of the petroleum system. The time has come for this same community to apply its considerable intellectual and operational acumen to optimizing another system that is rarely recognized as such: near-field exploration. Unlike “pure” conventional exploration, near-field exploration tends to be much more organizationally complex. Exploration functions need to deal with producing assets. Offices set in different cultures and separated by many time zones need to work together flawlessly. Engineering-centric dynamic geocellular models need to mesh with map-based static descriptions of the earth. Most importantly, a culture of value assurance needs to be balanced with a spirit of exploration that demands a culture of creativity and risk taking. These compartmentalized and layered oil and gas organizations share one important characteristic with the heterogeneous earth: each component can be considered to have its own unique impedance. As all interpreters know, elastic impedance contrasts associated with geological heterogeneity give rise to reflected seismic signals, the acquisition, processing, and interpretation of which are our bread and butter. Yet while organizational boundaries also impede the free flow of energy (in the form of knowledge/information, processes, workflows, etc.), there is little awareness that signals reflected from organizational impedance contrasts can be studied and ultimately inverted to understand and optimize various organizational components. Taken together, the heterogeneous environment known as near-field exploration can be modeled as a complex arrangement of different types of impedances, with (usually unmonitored) signals emanating from the many impedance contrasts. The monitoring, processing, and interpretation of these organizational signals are shown to fit well into the Shewhart cycle of plan-do-check-act, something that our engineering colleagues use regularly in their lean manufacturing processes. This paper introduces what for many will be a new paradigm for the organizational development of companies focused on near-infrastructure exploration. And yet for most interpreters reading this, it will seem “old hat.” Our community has been unmasking the geology associated with boundary reflections for almost a century. The time has come to improve the organizations within which we toil by applying our skills to the study of organizational impedance contrasts.
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Schmitt, Susanne, and Andreas Kirsch. "A factorization scheme for determining conductivity contrasts in impedance tomography." Inverse Problems 27, no. 9 (August 8, 2011): 095005. http://dx.doi.org/10.1088/0266-5611/27/9/095005.
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Niccoli, Matteo. "Mapping and validating lineaments." Leading Edge 34, no. 8 (August 2015): 948–50. http://dx.doi.org/10.1190/tle34080948.1.
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Data enhancement can help to emphasize edges that correspond to contrasts in acoustic impedance, magnetic susceptibility, or bulk density. Such contrasts often indicate the presence of important geologic boundaries. Emphasizing the edges can help with mapping and interpretation of those boundaries.
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Douma, Huub, David Yingst, Ivan Vasconcelos, and Jeroen Tromp. "On the connection between artifact filtering in reverse-time migration and adjoint tomography." GEOPHYSICS 75, no. 6 (November 2010): S219—S223. http://dx.doi.org/10.1190/1.3505124.
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Finite-frequency sensitivity kernels in seismic tomography define the volumes inside the earth that influence seismic waves as they traverse through it. It has recently been numerically observed that an image obtained using the impedance kernel is much less contaminated by low-frequency artifacts due to the presence of sharp wave-speed contrasts in the background model, than is an image obtained using reverse-time migration. In practical reverse-time migration, these artifacts are routinely heuristically dampened by Laplacian filtering of the image. Here we show analytically that, for an isotropic acoustic medium with constant density, away from sources and receivers and in a smooth background medium, Laplacian image filtering is identical to imaging with the impedance kernel. Therefore, when imaging is pushed toward using background models with sharp wave-speed contrasts, the impedance kernel image is less prone to develop low-frequency artifacts than is the reverse-time migration image, due to the implicit action of the Laplacian that amplifies the higher-frequency reflectors relative to the low-frequency artifacts. Thus, the heuristic Laplacian filtering commonly used in practical reverse-time migration is fundamentally rooted in adjoint tomography and, in particular, closely connected to the impedance kernel.
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Amundsen, Lasse, Bjørn Ursin, and Martin Landrø. "The plane-wave primary reflection response from an impedance gradient interface." Journal of the Acoustical Society of America 152, no. 1 (July 2022): 659–66. http://dx.doi.org/10.1121/10.0012885.
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A weak scattering model that allows prediction of the one-dimensional acoustic plane wave primary reflection response from an impedance gradient interface is described. The velocity and density gradient profiles are represented by a smooth approximation to the Heaviside function of the Fermi–Dirac distribution type. The profiles are described by the velocities and densities at minus and plus infinity, the reference depth of the gradient interface, and its smoothness. The primary response is derived by using the Bremmer series to reduce a generally complex reflection problem to the simpler one of the primary reflections which is a valid solution for small impedance contrasts. The reflection response can be expressed in terms of the Appellian hypergeometric functions of two variables of the first kind and Gaussian hypergeometric functions. When the reflection response is evaluated at sufficiently large distance above the reference depth, the Appellian functions are reduced to Gaussian hypergeometric functions. In the Born approximation, the reflection response simplifies. In the limit of zero frequency, the reflection coefficient in the small impedance contrast approximation can be related to the classic reflection coefficient for two impedance layers in welded contact.
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Samore, Andrea, Marco Guermandi, Silvio Placati, and Roberto Guerrieri. "Parametric Detection and Classification of Compact Conductivity Contrasts With Electrical Impedance Tomography." IEEE Transactions on Instrumentation and Measurement 66, no. 10 (October 2017): 2666–79. http://dx.doi.org/10.1109/tim.2017.2711818.
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Kenter, J. A. M., G. L. Bracco Gartner, and W. Schlager. "Seismic models of a mixed carbonate‐siliciclastic shelf margin: Permian upper San Andres Formation, Last Chance Canyon, New Mexico." GEOPHYSICS 66, no. 6 (November 2001): 1744–48. http://dx.doi.org/10.1190/1.1487116.
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Seismic models based on randomly distributed samples from the Permian upper San Andres Formation (Last Chance Canyon, New Mexico) verify that the most prominent seismic reflections are related to stratal geometry. However, at least some reflections arise from lateral facies transitions that are commonly associated with highly prograding mixed carbonate‐siliciclastic sediments. Understanding seismic reflections and reflection terminations in sedimentary rocks requires simulation of at least 2‐D cross‐sections of the impedance distribution. To investigate the cause of reflections in strongly prograding mixed carbonate‐siliciclastic shelf margins, acoustic velocity and bulk density were measured on more than 60 plugs that spatially cover one higher order genetic sequence. The resulting impedance values were gridded and contoured, and the genetic sequence was repeated to create a cross‐section. Averaging impedance values for each lithofacies zone generated a second impedance cross‐section. Seismic models of both impedance cross‐sections revealed the following observations: (1) reflections associated with the sequence boundaries are subject to amplitude and polarity phase changes and (2) at least one reflection within the high‐order sequences is related to subhorizontal facies changes and is associated with two pseudounconformities. The contoured impedance model is suggested to closer resemble the true impedance function in outcrop and shows subtle vertical shifts and significantly higher impedance contrasts.
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Pilz, Marco, and Fabrice Cotton. "Does the One-Dimensional Assumption Hold for Site Response Analysis? A Study of Seismic Site Responses and Implication for Ground Motion Assessment Using KiK-Net Strong-Motion Data." Earthquake Spectra 35, no. 2 (May 2019): 883–905. http://dx.doi.org/10.1193/050718eqs113m.
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The one-dimensional (1-D) approach is still the dominant method to incorporate site effects in engineering applications. To bridge the 1-D to multidimensional site response analysis, we develop quantitative criteria and a reproducible method to identify KiK-net sites with significant deviations from 1-D behavior. We found that 158 out of 354 show two-dimensional (2-D) and three-dimensional (3-D) effects, extending the resonance toward shorter periods at which 2-D or 3-D site effects exceed those of the classic 1-D configurations and imposing an additional amplification to that caused by the impedance contrast alone. Such 2-D and 3-D effects go along with a large within-station ground motion variability. Remarkably, these effects are found to be more pronounced for small impedance contrasts. While it is hardly possible to identify common features in ground motion behavior for stations with similar topography typologies, it is not over-conservative to apply a safety factor to account for 2-D and 3-D site effects in ground motion modeling.
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Martinez, Ruben D., and George A. McMechan. "Analysis of absorption and dispersion effects in synthetic τ-p seismograms." GEOPHYSICS 52, no. 8 (August 1987): 1033–47. http://dx.doi.org/10.1190/1.1442369.
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Analysis of absorption and dispersion effects may be done in intercept time‐ray parameter (τ-p) synthetic seismograms calculated using the slowness formulation of the reflectivity method. Seismograms initially computed in the frequency‐ray parameter (ω-p) domain to incorporate absorption and dispersion effects are then Fourier transformed to the (τ-p) domain. Absorption and dispersion are functions of p. Modeling both simple and more realistic stratigraphic sequences shows the interaction of only velocity and density for infinite Q and the complicated effects added when Q is finite. The observed null reflection at p = 0 for infinite Q is no longer null when Q is finite. For p ≠ 0, the inclusion of absorption and dispersion effects complicates the amplitude and phase of the seismic response. Reflectivity due to Q alone (i.e., at an interface with no impedance contrast), as a function of Q contrast and p, contains interesting variations of amplitude and phase. The responses of three geologically realistic models (a brine sand, a partially saturated gas sand, and an ocean‐sediment interface) demonstrate the cumulative nature of the attenuation effect and how the Q contributions become dominant when the acoustic impedance contrast is small. For large acoustic impedance contrasts, the attenuation effect occurs as an amplitude decay and phase rotation for some (especially high) frequencies. The modeling results suggest that absorption and dispersion effects should be taken into account in seismic inversion. Q estimations (in addition to velocity and density) are particularly desirable in exploration for hydrocarbons because of the sensitivity of Q to lithology and fluid content. Q contributes to the reflectivity information inherent in the seismic data.
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Tipper, John C. "Do seismic reflections necessarily have chronostratigraphic significance?" Geological Magazine 130, no. 1 (January 1993): 47–55. http://dx.doi.org/10.1017/s0016756800023712.
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AbstractMany seismic reflections from within sedimentary successions are thought to be generated along stratal surfaces because those surfaces are laterally continuous and have marked acoustic impedance contrasts. As stratal surfaces are isochronous, those reflections are then also taken as being chronostratigraphically significant. In contrast, seismic reflections are thought not to be generated along the boundaries of lithostratigraphic units because those boundaries are discontinuous and gradational. Nevertheless, synthetic seismic analysis shows that seismic reflections should in many circumstances be expected to follow lithostratigraphic unit boundaries, not stratal surfaces. As these lithostratigraphic unit boundaries will generally be diachronous, seismic reflections from within sedimentary successions should evidently not be treated as necessarily having chronostratigraphic significance.
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Colombero, Chiara, Cesare Comina, and Laura Valentina Socco. "Imaging near-surface sharp lateral variations with surface-wave methods — Part 1: Detection and location." GEOPHYSICS 84, no. 6 (November 1, 2019): EN93—EN111. http://dx.doi.org/10.1190/geo2019-0149.1.
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Near-surface sharp lateral variations can be either a target of investigation or an issue for the reconstruction of reliable subsurface models in surface-wave (SW) prospecting. Effective and computationally fast methods are consequently required for detection and location of these shallow heterogeneities. Four SW-based techniques, chosen between available literature methods, are tested for detection and location purposes. All of the techniques are updated for multifold data and then systematically applied on new synthetic and field data. The selected methods are based on computation of the energy, energy decay exponent, attenuation coefficient, and autospectrum. The multifold upgrade is based on the stacking of the computed parameters for single-shot or single-offset records and improves readability and interpretation of the final results. Detection and location capabilities are extensively evaluated on a variety of 2D synthetic models, simulating different target geometries, embedment conditions, and impedance contrasts with respect to the background. The methods are then validated on two field cases: a shallow low-velocity body in a sedimentary sequence and a hard-rock site with two embedded subvertical open fractures. For a quantitative comparison, the horizontal gradients of the four parameters are analyzed to establish uniform criteria for location estimation. All of the methods indicate ability in detecting and locating lateral variations having lower acoustic impedance than the surrounding material, with errors generally comparable or lower than the geophone spacing. More difficulties are encountered in locating targets with higher acoustic impedance than the background, especially in the presence of weak lateral contrasts, high embedment depths, and small dimensions of the object.
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de Matos, Marcílio Castro, Rodrigo Penna, Paulo Johann, and Kurt Marfurt. "Relative acoustic impedance from wavelet transform." Interpretation 2, no. 1 (February 1, 2014): SA107—SA118. http://dx.doi.org/10.1190/int-2013-0090.1.
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Most deconvolution algorithms try to transform the seismic wavelet into spikes by designing inverse filters that remove an estimated seismic wavelet from seismic data. We assume that seismic trace subtle discontinuities are associated with acoustic impedance contrasts and can be characterized by wavelet transform spectral ridges, also called modulus maxima lines (WTMML), allowing us to improve seismic resolution by using the wavelet transform. Specifically, we apply the complex Morlet continuous wavelet transform (CWT) to each seismic trace and compute the WTMMLs. Then, we reconstruct the seismic trace with the inverse continuous wavelet transform from the computed WTMMLs with a broader band complex Morlet wavelet than that used in the forward CWT. Because the reconstruction process preserves amplitude and phase along different scales, or frequencies, the result looks like a deconvolution method. Considering this high-resolution seismic representation as a reflectivity approximation, we estimate the relative acoustic impedance (RAI) by filtering and trace integrating it. Conventional deconvolution algorithms assume the seismic wavelet to be stochastic, while the CWT is implicitly time varying such that it can be applied to both depth and time-domain data. Using synthetic and real seismic data, we evaluated the effectiveness of the methodology on detecting seismic events associated with acoustic impedance changes. In the real data examples, time and in-depth RAI results, show good correlation with real P-impedance band-pass data computed using more rigorous commercial inversion software packages that require well logs and low-frequency velocity model information.
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Justice, James H., and Chris Zuba. "Transition zone reflections and permafrost analysis." GEOPHYSICS 51, no. 5 (May 1986): 1075–86. http://dx.doi.org/10.1190/1.1442163.
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The usual study of seismic reflections is limited to those from sharply defined contrasts in acoustic impedance. For reflections resulting from transition zones in which acoustic impedance is continuously variable (such as the zones encountered in permafrost), the frequency‐selective nature of attenuation and phase distortion leads to a number of characteristics which may be used in the sense of pattern recognition to identify such reflections. An rms velocity‐analysis procedure can be used to estimate depths and velocity gradients associated with transition zones. Some simple approximations allow us to avoid solving a system of nonlinear equations in many cases of interest, and the result is a practical technique which can be applied to many transition zone reflections at reasonable computational cost.
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Rabben, Tor Erik, and Bjørn Ursin. "AVA inversion of the top Utsira Sand reflection at the Sleipner field." GEOPHYSICS 76, no. 3 (May 2011): C53—C63. http://dx.doi.org/10.1190/1.3567951.
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Amplitude variation with angle (AVA) inversion is performed on the top Utsira Sand reflector at the Sleipner field, North Sea, Norway. This interface is of particular interest because of the accumulation of [Formula: see text] injected from a point deeper in the Utsira Sand. The focus is on the postmigration processing of angle gathers together with the actual inversion procedure. The processing treats amplitude extraction, offset-to-angle mapping, and global scaling in detail. Two algorithms are used for the inversion of AVA data, one that assesses uncertainties and one fast least-squares variant. Both are very suitable for this type of problem because of their covariance matrices and built-in regularization. In addition, two three-parameter approximations of the Zoeppritz equations are used. One is linear approximation and the other is quadratic. The results show significant signals for all three elastic parameters, but the substitution of brine by [Formula: see text] using Gassmann’s equation indicates that the contrasts in S-wave impedance and density are overestimated. For the contrasts in P-wave impedance the results are in agreement with the fluid substitution. A simple sensitivity analysis shows that the offset-to-angle mapping and the damping factor in the inversion are the most plausible explanations of the discrepancy.
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Hobro, James W. D., Chris H. Chapman, and Johan O. A. Robertsson. "A method for correcting acoustic finite-difference amplitudes for elastic effects." GEOPHYSICS 79, no. 4 (July 1, 2014): T243—T255. http://dx.doi.org/10.1190/geo2013-0335.1.
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We present a new method for correcting the amplitudes of arrivals in an acoustic finite-difference simulation for elastic effects. In this method, we selectively compute an estimate of the error incurred when the acoustic wave equation is used to approximate the behavior of the elastic wave equation. This error estimate is used to generate an effective source field in a second acoustic simulation. The result of this second simulation is then applied as a correction to the original acoustic simulation. The overall cost is approximately twice that of an acoustic simulation but substantially less than the cost of an elastic simulation. Because both simulations are acoustic, no S-waves are generated, so dispersed converted waves are avoided. We tested the characteristics of the method on a simple synthetic model designed to simulate propagation through a strong acoustic impedance contrast representative of sedimentary geology. It corrected amplitudes to high accuracy for reflected arrivals over a wide range of incidence angles. We also evaluated results from simulations on more complex models that demonstrated that the method was applicable in realistic sedimentary models containing a wide range of seismic contrasts. However, its accuracy was reduced for wide-angle reflections from very high impedance contrasts such as a shallow top-salt interface. We examined the influence of modeling at coarse grid resolutions, in which converted S-waves in the equivalent elastic simulation are dispersed. These results provide some validation for the accuracy of the method when applied using finite-difference grids designed for acoustic modeling. The method appears to offer a cost-effective means of modeling elastic amplitudes for P-wave arrivals in a useful range of velocity models. It has several potential applications in imaging and inversion.
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Douma, Huub, and Kabir Roy-Chowdhury. "Amplitude effects due to multiscale impedance contrasts and multiple scattering: implications for Ivrea-type continental lower crust." Geophysical Journal International 147, no. 2 (November 2001): 435–48. http://dx.doi.org/10.1046/j.1365-246x.2001.00537.x.
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Anandakrishnan, Sridhar. "Dilatant till layer near the onset of streaming flow of Ice Stream C, West Antarctica, determined by AVO (amplitude vs offset) analysis." Annals of Glaciology 36 (2003): 283–86. http://dx.doi.org/10.3189/172756403781816329.
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AbstractA powerful seismic technique that exploits the phase of the ice-bottom reflections shows that soft till is widespread beneath a West Antarctic ice stream very close to the onset of streaming flow. The amplitude vs offset (AVO) method measures the change in amplitude of the reflection as a function of increasing angle of incidence. For a decrease in acoustic impedance with depth, the reflection phase is negative at low angles of impedance but positive at intermediate angles. The change in phase by 180° is an obvious and robust measure of the relative acoustic impedance contrasts. This technique is only usable when there is a change in phase vs offset, conditions which obtain for “UpB-type” tills (high water pressures and porosity, low compressional- and shear-wave velocities, similar to those observed at Upstream B camp). I have applied this technique to the far upstream regions of Ice Stream C and find that a dilatant ( and presumably deforming), relatively thick (meters) till layer has formed beneath the ice stream within tens of km of the region identified as the transition from inland flow to ice-stream flow. These results suggest that the onset of rapid basal motion is linked to the formation of this deforming subglacial layer.
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Agarwal, Shivani, and Toran Verma. "Modulation Control of Impedance Inverter to Achieve Simple, Constant and Maximum Boosted Output." Journal of Futuristic Sciences and Applications 4, no. 2 (2021): 22–30. http://dx.doi.org/10.51976/jfsa.422104.
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In order to provide a sustainable option for the generation of electricity, grid integration of PV panels is becoming more popular in developing nations. A PV module with a grid-coupled inverter makes up an AC module used to capture solar energy. Transformerless single stage AC module layouts are among the most effective configurations. Since its first release in 2003, ZSI, one of these arrangements, has seen a rapid evolution that has seen it adopt new topologies and control and modulation strategies to improve its performance from a variety of angles. This study compares and contrasts the modulation techniques used for 3-ZSI in order to highlight their fundamental differences. It then offers a practical method for obtaining high output voltage with minimal voltage stress on the inverter’s switching components.
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Gharibi, Mehran, and Laust B. Pedersen. "Transformation of VLF data into apparent resistivities and phases." GEOPHYSICS 64, no. 5 (September 1999): 1393–402. http://dx.doi.org/10.1190/1.1444644.
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In the VLF method, the ratio between the vertical and the horizontal magnetic field or the total magnetic field anomaly is measured to detect localized changes in electrical conductivity contrasts. Although the VLF technique has probably been the most popular electromagnetic (EM) tool for mapping near‐surface geological structures in a large scale for the past few decades because of the low cost and speed with which surveys can be carried out, the measurements themselves do not give a direct estimate of electrical conductivity. A fast iterative method has been developed to estimate the impedance or apparent resistivity and phases from measurements of the magnetic components at the surface of a 2-D geological structure. From Maxwell’s equations in E-polarization, a relation was derived between the horizontal and vertical components of the magnetic field. A full solution has been obtained by making use of the fact that the secondary horizontal and vertical magnetic fields are of internal origin and form a Hilbert transform pair. Synthetic and real VLF data have been used to evaluate the performance and limitation of the method. Using synthetic and real data, one can achieve a full recovery of the E-polarization impedance as long as the length of the profile is sufficiently long. A number of precautions must be taken to ensure reliable estimation of impedance results.
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García-Violini, Demián, Nicolás Faedo, Fernando Jaramillo-Lopez, and John V. Ringwood. "Simple Controllers for Wave Energy Devices Compared." Journal of Marine Science and Engineering 8, no. 10 (October 13, 2020): 793. http://dx.doi.org/10.3390/jmse8100793.
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The design of controllers for wave energy devices has evolved from early monochromatic impedance-matching methods to complex numerical algorithms that can handle panchromatic seas, constraints, and nonlinearity. However, the potential high performance of such numerical controller comes at a computational cost, with some algorithms struggling to implement in real-time, and issues surround convergence of numerical optimisers. Within the broader area of control engineering, practitioners have always displayed a fondness for simple and intuitive controllers, as evidenced by the continued popularity of the ubiquitous PID controller. Recently, a number of energy-maximising wave energy controllers have been developed based on relatively simple strategies, stemming from the fundamentals behind impedance-matching. This paper documents this set of (5) controllers, which have been developed over the period 2010–2020, and compares and contrasts their characteristics, in terms of energy-maximising performance, the handling of physical constraints, and computational complexity. The comparison is carried out both analytically and numerically, including a detailed case study, when considering a state-of-the-art CorPower-like device.
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Djikpéssé, Hugues A., and Albert Tarantola. "Multiparameter 𝓁1 norm waveform fitting: Interpretation of Gulf of Mexico reflection seismograms." GEOPHYSICS 64, no. 4 (July 1999): 1023–35. http://dx.doi.org/10.1190/1.1444611.
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Estimation of the elastic properties of the crust from surface seismic recordings is of great importance for the understanding of lithology and for the detection of mineral resources. Although in marine reflection experiments only P-waves are recorded, information on shear properties of the medium is contained in multioffset reflection seismograms. Being able to retrieve both dilatational and shear properties gives stronger constraints on the lithology. It is therefore desirable to recover isotropic elastic parameters from multioffset seismograms. Unfortunately, most classical waveform fitting methods used for extracting shear properties of the subsurface are based on a 1-D earth model assumption and on linear approximations of the wave equations. In this paper, a 2.5-D elastic waveform inversion method is used to extract the variations of acoustic impedance and Poisson’s ratio from marine multioffset reflection seismograms collected in the Gulf of Mexico area. A complete seismic profile is interpreted, including complex physical phenomena apparent in the data, such as unconsolidated sediment reflections and seismic refraction events. The amplitude of the reflections cannot be explained by one parameter related to the dilatational properties (P-impedance) only, when trying to minimize the least absolute fit between observed and synthetic seismograms. When adding an additional parameter related to shear properties (Poisson’s ratio), the fit between observed and synthetic seismograms improves. The resulting 2-D models of P-impedance and Poisson’s ratio contrasts are anticorrelated almost everywhere in depth, except where hydrocarbons are present. The estimation of physical P-impedance and Poisson’s ratio models by a full waveform fitting allows lithology characterization and, therefore, the delineation of a shale‐over‐gas sand reservoir.
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Ross, R., L. Leger, P. Martin, and R. Roy. "Sensitivity of bioelectrical impedance to detect changes in human body composition." Journal of Applied Physiology 67, no. 4 (October 1, 1989): 1643–48. http://dx.doi.org/10.1152/jappl.1989.67.4.1643.
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The purpose of this study was to compare the estimates of lean body mass (LBM) and percent body fat (%BF), as predicted by bioelectrical impedance (BIA) and sum of skinfolds (SF), with those derived by hydrostatic weighing (HW) obtained before and after a 10-wk diet and exercise regimen. The experimental (E) group consisted of 17 healthy male subjects; 20 healthy males served as the control (C) group. Post hoc Scheffe contrasts computed on E group data indicated that, for both LBM and %BF, the Lukaski and Segal BIA equations, as well as the Durnin SF equation, derived mean values that were not significantly different (0.05 significance level) from HW in both pre- and postregimen conditions. For LBM, the same equations derived the following significant (P less than 0.01) correlation coefficients for both pre- and postregimen data: Lukaski, 0.87 and 0.85; Segal, 0.89 and 0.87; and Durnin, 0.90 and 0.88. For %BF, the correlation coefficients were slightly lower but remained statistically significant (P less than 0.01). The findings of this study suggest that the BIA method, by use of either the Lukaski or Segal prediction equations, is a valid means of predicting changes in human body composition as measured by the Siri transformation of body density.
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Dai, Wen Jin, and Xiang Jie Chen. "Analysis for TCSC in Single Phase Power System Simulation." Advanced Materials Research 179-180 (January 2011): 20–27. http://dx.doi.org/10.4028/www.scientific.net/amr.179-180.20.
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This paper carries on the stable state simulation and transition condition simulation for the single phase power systems, which are without TCSC and with TCSC systems. Both without TCSC and with TCSC circuits in the single-phase power system, have been carried out a detailed steady state and transition condition simulation, and studied the influence for TCSC that on power system load voltage and load power. In addition, applies the TCSC conventional PID impedance control mode, with TCSC fuzzy PID impedance control in the electrical power system, contrasts their function that display in the electrical power system operation, and demonstrate the two controllers’ advantage and disadvantage. In the stable state simulation, establishes the systems operation separately in the two kind of situations that rated load and overload, observes the respective load voltage profile, and carries on the comparison with other, in order to study the function for TCSC that work s in the single phase power system normal operation time . In the transition condition simulation, establishment short trouble, views the system transition condition’s load voltage, makes its profile the comparison, and studies TCSC in the single phase power system transition condition function. At the same time, considered the difference for TCSC impedance control modes, as well each as the influence which produces to the TCSC performance characteristic, makes the TCSC conventional PID impedance control mode and TCSC fuzzy PID impedance control mode to apply in the single phase power system separately, and carries on the two's simulation profile in detail contrastive analysis . The simulation result indicated that TCSC has the tidal current control and the damping line power vibration, enhances the electrical power system transition condition stably many kinds of functions, in the stable state condition, TCSC can increase system's transportation power, and reduce the electric transmission loss; under the transition condition, TCSC can suppress the system power oscillation and enhance the system stability.
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Qi, Chen, and Fred Hilterman. "Well ties for seismic with severe stratigraphic filtering." GEOPHYSICS 82, no. 5 (September 1, 2017): IM31—IM39. http://dx.doi.org/10.1190/geo2016-0695.1.
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Stratigraphic filtering (SF), or short-period multiples, is prominent in cyclically stratified sedimentation with large impedance contrasts that result in normal-incident reflection magnitudes greater than 0.5. Because SF attenuates and delays the propagating wavelet, similar to the effects of [Formula: see text] attenuation, the integrity of well ties is often jeopardized. A method is proposed to obtain better well ties in areas with severe SF. Starting with a well-log acoustic impedance curve, two-way transmitted wavefields and their equivalent inverse filters are generated at each time sample. Because a time-varying convolution of the transmitted wavefields with the primary-only reflectivity yields the multiple reflectivity, a time-varying deconvolution of the multiple synthetic with the inverse filters yields the primary-only reflectivity. In essence, when the multiple synthetic matches the near-angle stack at a well location, the near-angle stack is deconvolved in a time-varying fashion to match the primary-only synthetic, which then constitutes a correlation with the acoustic impedance yielding a good well tie. This new well-tie technique preserves the integrity of the lithologic interpretation because stretching and squeezing the time scale of the primary-only synthetic to force a seismic match are avoided. Our well-tie method is applied to the synthetic and field data from Cooper Basin, Australia, where more than 30 coal beds are observed within a 1000 ft (304 m) interval.
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Kumar Katiyar, Sudhir, and Mohan Gupta. "Modulation Control of Impedance Inverter to achieve Simple and Maximum Boosted Output." Journal of Futuristic Sciences and Applications 2, no. 2 (2019): 31–39. http://dx.doi.org/10.51976/jfsa.221905.
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India has seen a notable increase in adoption of the renewable energy, Various policies and schemes had been proposed in India to focalize on renewable energy sector. For solar energy conversion, an AC module that functions as a grid-connected inverter after a PV module is needed. ZSI is being used to alleviate a myriad of issues that VSI and CSI have. An impedance source inverter provided with triggering pulses generated by maximum boost control modulation technique is presented in this paper. The shoot-through control approach that is utilized to generate pulses that are sent to semiconductor switches is directly related to the output voltage of the ZSI. Among the several techniques that can be used, the one that involves the least amount of complexity is the one that is used here. The output of PV module which is mostly of lower range must be increased in able to link to the grid due to its inconsistent and fluctuating nature. This study compares and contrasts the modulation techniques used for 3-ZSI in order to highlight their fundamental differences. It then offers a practical method for obtaining high output voltage with minimal voltage stress on the inverter's switching components.
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Jerome, Thomas S., and Mark F. Hamilton. "Born approximation of acoustic radiation force and torque." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A89. http://dx.doi.org/10.1121/10.0010752.
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The Born approximation provides a simple method for calculating acoustic radiation force and torque on compressible objects of arbitrary shape, which may be inhomogeneous. The specific acoustic impedance throughout the object must not differ significantly from that of the background fluid. Also, the incident field must not be too similar to a progressive plane wave, because the approximation is associated with radiation forces due to time-averaged energy density gradients in the incident field. Comparisons with a complete theory for radiation force and torque exerted by standing plane waves on compressible spheroids, based on expansions of the incident and scattered fields in spheroidal wave functions, indicate that the Born approximation is accurate for impedance contrasts up to at least 30% and for spheroids with sizes on the order of a wavelength. This presentation will review the derivation, validation, and applications of the Born approximation. Closed-form solutions for spheres and finite cylinders are presented and for selected distributions of material inhomogeneity. Applications include acoustofluidic separation of biological targets, and acoustic forces on nonspherical objects near interfaces. The approximation also serves as a useful benchmark for other methods of calculation. [T.S.J. was supported by an ARL:UT McKinney Fellowship in Acoustics.]
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Jones, Ian F., and Ian Davison. "Seismic imaging in and around salt bodies." Interpretation 2, no. 4 (November 1, 2014): SL1—SL20. http://dx.doi.org/10.1190/int-2014-0033.1.
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Seismic imaging of evaporite bodies is notoriously difficult due to the complex shapes of steeply dipping flanks, adjacent overburden strata, and the usually strong acoustic impedance and velocity contrasts at the sediment-evaporite interface. We consider the geology of salt bodies and the problems and pitfalls associated with their imaging such as complex raypaths, seismic velocity anisotropy, P- and S-wave mode conversions, and reflected refractions. We also review recent developments in seismic acquisition and processing, which have led to significant improvements in image quality and in particular, reverse time migration. We tried to call attention to the form, nature, and consequences of these issues for meaningful interpretation of the resulting images.
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Adam, Erick, Bernd Milkereit, Marianne Mareschal, Arthur E. Barnes, Claude Hubert, and Matthew Salisbury. "The application of reflection seismology to the investigation of the geometry of near-surface units and faults in the Blake River Group, Abitibi Belt, Quebec." Canadian Journal of Earth Sciences 29, no. 9 (September 1, 1992): 2038–45. http://dx.doi.org/10.1139/e92-160.
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Reprocessing of part of a Lithoprobe high-resolution seismic reflection line across the southern part of the Abitibi Belt has improved the imaging of shallow reflections and allowed correlation of the data with surface geology. Enhancement of early reflections was accomplished by focusing on the high-frequency content of the data. This improved resolution of reflections at two-way traveltime as early as 0.3 s and attenuated noise such as shear waves. The shallow reflections are interpreted as impedance contrasts at the contact between a metadiabase–diorite body and metavolcanics rocks. Offsets of the reflectors correlate with faults mapped at the surface and indicate a downdropped block, which may be of interest for mineral exploration.
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Koemets, Iuliia, Niccolò Satta, Hauke Marquardt, Ekaterina S. Kiseeva, Alexander Kurnosov, Thomas Stachel, Jeff W. Harris, and Leonid Dubrovinsky. "Elastic properties of majoritic garnet inclusions in diamonds and the seismic signature of pyroxenites in the Earth's upper mantle." American Mineralogist 105, no. 7 (July 1, 2020): 984–91. http://dx.doi.org/10.2138/am-2020-7136ccby.
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Abstract Majoritic garnet has been predicted to be a major component of peridotite and eclogite in Earth's deep upper mantle (>250 km) and transition zone. The investigation of mineral inclusions in diamond confirms this prediction, but there is reported evidence of other majorite-bearing lithologies, intermediate between peridotitic and eclogitic, present in the mantle transition zone. If these lithologies are derived from olivine-free pyroxenites, then at mantle transition zone pressures majorite may form monomineralic or almost monomineralic garnetite layers. Since majoritic garnet is presumably the seismically fastest major phase in the lowermost upper mantle, the existence of such majorite layers might produce a detectable seismic signature. However, a test of this hypothesis is hampered by the absence of sound wave velocity measurements of majoritic garnets with relevant chemical compositions, since previous measurements have been mostly limited to synthetic majorite samples with relatively simple compositions. In an attempt to evaluate the seismic signature of a pyroxenitic garnet layer, we measured the sound wave velocities of three natural majoritic garnet inclusions in diamond by Brillouin spectroscopy at ambient conditions. The chosen natural garnets derive from depths between 220 and 470 km and are plausible candidates to have formed at the interface between peridotite and carbonated eclogite. They contain elevated amounts (12–30%) of ferric iron, possibly produced during redox reactions that form diamond from carbonate. Based on our data, we model the velocity and seismic impedance contrasts between a possible pyroxenitic garnet layer and the surrounding peridotitic mantle. For a mineral assemblage that would be stable at a depth of 350 km, the median formation depth of our samples, we found velocities in pyroxenite at ambient conditions to be higher by 1.9(6)% for shear waves and 3.3(5)% for compressional waves compared to peridotite (numbers in parentheses refer to uncertainties in the last given digit), and by 1.3(13)% for shear waves and 2.4(10)% for compressional waves compared to eclogite. As a result of increased density in the pyroxenitic layer, expected seismic impedance contrasts across the interface between the monomineralic majorite layer and the adjacent rocks are about 5–6% at the majorite-eclogite-interface and 10–12% at the majoriteperidotite-boundary. Given a large enough thickness of the garnetite layer, velocity and impedance differences of this magnitude could become seismologically detectable.
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Paolucci, Enrico, Giuseppe Cavuoto, Giuseppe Cosentino, Monia Coltella, Maurizio Simionato, Gian Paolo Cavinato, Isabella Trulli, and Dario Albarello. "Regional Seismic Characterization of Shallow Subsoil of Northern Apulia (Southern Italy)." Geosciences 11, no. 10 (October 6, 2021): 416. http://dx.doi.org/10.3390/geosciences11100416.
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A first-order seismic characterization of Northern Apulia (Southern Italy) has been provided by considering geological information and outcomes of a low-cost geophysical survey. In particular, 403 single-station ambient vibration measurements (HVSR techniques) distributed within the main settlements of the area have been considered to extract representative patterns deduced by Principal Component Analysis. The joint interpretation of these pieces of information allows the identification of three main domains (Gargano Promontory, Bradanic Through and Southern Apennines Fold and Thrust Belt), each characterized by specific seismic resonance phenomena. In particular, the Bradanic Through is homogeneously characterized by low frequency (<1 Hz) resonance effects associated with relatively deep (>100 m) seismic impedance, which is contrasting corresponding to the buried Apulian carbonate platform and/or sandy horizons located within the Plio-Pleistocene deposits. In the remaining ones, relatively high frequency (>1 Hz) resonance phenomena are ubiquitous due to the presence of shallower impedance contrasts (<100 m), which do not always correspond to the top of the geological bedrock. These general indications may be useful for a preliminary regional characterization of seismic response in the study area, which can be helpful for an effective planning of more detailed studies targeted to engineering purposes.
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Saldaña, Gaizka, José Ignacio San Martín, Inmaculada Zamora, Francisco Javier Asensio, and Oier Oñederra. "Analysis of the Current Electric Battery Models for Electric Vehicle Simulation." Energies 12, no. 14 (July 18, 2019): 2750. http://dx.doi.org/10.3390/en12142750.
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Electric vehicles (EVs) are a promising technology to reduce emissions, but its development enormously depends on the technology used in batteries. Nowadays, batteries based on lithium-ion (Li-Ion) seems to be the most suitable for traction, especially nickel-manganese-cobalt (NMC) and nickel-cobalt-aluminum (NCA). An appropriate model of these batteries is fundamental for the simulation of several processes inside an EV, such as the state of charge (SoC) estimation, capacity and power fade analysis, lifetime calculus, or for developing control and optimization strategies. There are different models in the current literature, among which the electric equivalent circuits stand out, being the most appropriate model when performing real-time simulations. However, impedance models for battery diagnosis are considered very attractive. In this context, this paper compares and contrasts the different electrical equivalent circuit models, impedance models, and runtime models for battery-based EV applications, addressing their characteristics, advantages, disadvantages, and usual applications in the field of electromobility. In this sense, this paper serves as a reference for the scientific community focused on the development of control and optimization strategies in the field of electric vehicles, since it facilitates the choice of the model that best suits the needs required.
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Joshi, Sharad, Ishwer Datt Gupta, Lalitha R. Pattanur, and Pranesh B. Murnal. "Investigating the Effect of Depth and Impedance of Foundation Rock in Seismic Analysis of Gravity Dams." International Journal of Geotechnical Earthquake Engineering 5, no. 2 (July 2014): 1–18. http://dx.doi.org/10.4018/ijgee.2014070101.
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The inhomogenieties of the foundation can be modeled explicitly in standard FEM procedure, however, the results vary significantly with the extent of foundation block modeled and mechanism of applying the input earthquake excitation. The substructure approach provides mathematically exact solution but assumes average properties for the entire foundation as viscoelastic half space. This paper has carried out detailed investigations with varying impedance contrasts and different size of foundation block to show that the results, with suitably deconvoluted free-field ground acceleration time-history applied at the base of foundation block in the FEM approach, are in good agreement with the substructure approach. However, the other variants of the FEM approach may lead to erroneous and overestimated stresses in the dam body. As the foundation of gravity dams can generally be approximated as an equivalent homogeneous half-space, the more accurate and efficient substructure approach can be used to model the dam-foundation rock interaction (SSI) effects in most practical situations.
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Meng, Zi Jun, Saurav Z. K. Sajib, Munish Chauhan, Rosalind J. Sadleir, Hyung Joong Kim, Oh In Kwon, and Eung Je Woo. "Numerical Simulations of MREIT Conductivity Imaging for Brain Tumor Detection." Computational and Mathematical Methods in Medicine 2013 (2013): 1–10. http://dx.doi.org/10.1155/2013/704829.
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Magnetic resonance electrical impedance tomography (MREIT) is a new modality capable of imaging the electrical properties of human body using MRI phase information in conjunction with external current injection. Recentin vivoanimal and human MREIT studies have revealed unique conductivity contrasts related to different physiological and pathological conditions of tissues or organs. When performingin vivobrain imaging, small imaging currents must be injected so as not to stimulate peripheral nerves in the skin, while delivery of imaging currents to the brain is relatively small due to the skull’s low conductivity. As a result, injected imaging currents may induce small phase signals and the overall low phase SNR in brain tissues. In this study, we present numerical simulation results of the use of head MREIT for brain tumor detection. We used a realistic three-dimensional head model to compute signal levels produced as a consequence of a predicted doubling of conductivity occurring within simulated tumorous brain tissues. We determined the feasibility of measuring these changes in a time acceptable to human subjects by adding realistic noise levels measured from a candidate 3 T system. We also reconstructed conductivity contrast images, showing that such conductivity differences can be both detected and imaged.
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Halverson, Jens R. "Seismic expression of the Upper Morrow sands, western Anadarko Basin." GEOPHYSICS 53, no. 3 (March 1988): 290–303. http://dx.doi.org/10.1190/1.1442463.
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In the western Anadarko Basin, the Lower Pennsylvanian Upper Morrow sands are both a prolific and an elusive exploration target. Initial production from some of these sands can reach well over 1000 barrels of oil per day, and yet an offset well just 350 m away from a good producer can miss the Morrow sand entirely and result in a dry hole. One‐dimensional merged log modeling, two‐ dimensional log interpolation modeling, color seismic inversion processing, and seismic facies mapping techniques have been applied to the Lear and Darden fields, two Upper Morrow sand fields in the Texas Panhandle. Here the Morrow sands reach an isopach thickness of 10 to 15 m at a depth of 2500 to 3000 m. These Morrow sands are within the thin‐bed regime (below the tuning point) so that there is a correlation between the amplitude of the reflection and the thickness of the sand. The velocity and density contrasts of the shales and sands are sufficient to produce a good acoustic impedance contrast, making the sands detectable on seismic data with good signal‐to‐noise ratios. The comparison of geologic isopach mapping and geophysical seismic facies mapping shows an excellent correlation in the delineation of the Upper Morrow sands.
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Haines, A. J., and Jaishun Yu. "Observation and synthesis of spatially-incoherentweak-motion wavefields at Alfredton basin, New Zealand." Bulletin of the New Zealand Society for Earthquake Engineering 30, no. 1 (March 31, 1997): 14–31. http://dx.doi.org/10.5459/bnzsee.30.1.14-31.
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To observe and model the detailed pattern of ground motion amplification in a small soft-soil basin an experiment was conducted at Alfredton, New Zealand. 19 seismometers were deployed for 5 weeks at closely spaced sites in and around a 400-500 m diameter, sediment-filled depression in soft, sandstone basement. During this period 112 earthquakes, with "weak" ground motions, were detected by at least some of the instruments, and 15 well-recorded events were selected for detailed analysis. Geotechnical data obtained to provide the parameters for the 3-dimensional modelling included measurements of the shear-wave velocity. Across the basin this is 60 m/s at the surface, increasing steadily to 300+ m/s at the bottom of the basin, and the shear-wave velocity in the basement is 850 m/s. Thus, there are no boundaries where the contrast in shear-wave impedance is especially large.
In contrast to situations where there are large contrasts in shear-wave impedance to trap seismic energy in soft-soil layers, the amplifications observed in the basin at Alfredton were small. The small amplifications are confirmed by the 3-dimensional modelling. Another feature of the observed wavefields is that in all cases the incident motions, recorded at the basement sites around the basin, were spatially incoherent. In other words, the wavefields arriving at the basin were of a complex, seemingly random nature. This is the first occasion that the spatial coherency of wavefields has been measured in a fine-scale experiment in New Zealand. Apart from the small amplications and the observed lack of coherency between the basement sites, the most striking result, which was obtained from both the observations and the modelling of similarly incoherent wavefields, is that for short-duration events in which the main motions last for no more than a second, the amplifications in the basin are larger than for events in which the motions are of longer duration; that is, the extent to which differently propagating incoherent wave packets interfere destructively inside the basin increases with the duration of the wavefields.
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Ramos, Antonio C. B., and Thomas L. Davis. "3-D AVO analysis and modeling applied to fracture detection in coalbed methane reservoirs." GEOPHYSICS 62, no. 6 (November 1997): 1683–95. http://dx.doi.org/10.1190/1.1444268.
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Over the years, amplitude variation with‐offset (AVO) analysis has been used successfully to predict reservoir properties and fluid contents, in some cases allowing the spatial location of gas‐water and gas‐oil contacts. In this paper, we show that a 3-D AVO technique also can be used to characterize fractured reservoirs, allowing spatial location of crack density variations. The Cedar Hill Field in the San Juan Basin, New Mexico, produces methane from the fractured coalbeds of the Fruitland Formation. The presence of fracturing is critical to methane production because of the absence of matrix permeability in the coals. To help characterize this coalbed reservoir, a 3-D, multicomponent seismic survey was acquired in this field. In this study, prestack P‐wave amplitude data from the multicomponent data set are used to delineate zones of large Poisson's ratio contrasts (or high crack densities) in the coalbed methane reservoir, while source‐receiver azimuth sorting is used to detect preferential directions of azimuthal anisotropy caused by the fracturing system of coal. Two modeling techniques (using ray tracing and reflectivity methods) predict the effects of fractured coal‐seam zones on angle‐dependent P‐wave reflectivity. Synthetic common‐midpoint (CMP) gathers are generated for a horizontally layered earth model that uses elastic parameters derived from sonic and density log measurements. Fracture density variations in coalbeds are simulated by anisotropic modeling. The large acoustic impedance contrasts associated with the sandstone‐coal interfaces dominate the P‐wave reflectivity response. They far outweigh the effects of contrasts in anisotropic parameters for the computed models. Seismic AVO analysis of nine macrobins obtained from the 3-D volume confirms model predictions. Areas with large AVO intercepts indicate low‐velocity coals, possibly related to zones of stress relief. Areas with large AVO gradients identify coal zones of large Poisson's ratio contrasts and therefore high fracture densities in the coalbed methane reservoir. The 3-D AVO product and Poisson's variation maps combine these responses, producing a picture of the reservoir that includes its degree of fracturing and its possible stress condition. Source‐receiver azimuth sorting is used to detect preferential directions of azimuthal anisotropy caused by the fracturing system of coal.
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Wang, Siheng, Ting Chen, Nao Cai, Xintong Qi, Adrian Fiege, Robert C. Liebermann, and Baosheng Li. "Pressure-induced velocity softening in natural orthopyroxene at mantle temperature." American Mineralogist 104, no. 8 (August 1, 2019): 1173–79. http://dx.doi.org/10.2138/am-2019-6935.
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Abstract In this study, we have measured the compressional and shear wave velocities of (Mg1.77Fe0.22Ca0.01)Si2O6 natural orthopyroxene up to 13.5 GPa and 873 K using ultrasonic interferometry in conjunction with in situ synchrotron X-ray diffraction and imaging techniques. Previous acoustic experiments on orthoenstatite (OEn) MgSiO3 indicated that both compressional and shear velocities (VP and VS) of OEn undergo continuous velocity softening above 9 GPa at room temperature, which has been attributed to the phase transition from OEn to the metastable, high-pressure clinoenstatite HPCEn2. For the first time, our results suggest that pressure-induced velocity softening can occur in natural orthopyroxene at high-temperature conditions relevant to the Earth's cold subduction zones. Estimates of the impedance and velocity contrasts between orthopyroxene (Opx) and high-pressure clinopyroxene (HPCpx) have been calculated, and the possibility of this phase transformation being a plausible candidate for seismic X-discontinuities at depth around 250–350 km is re-evaluated.
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Titze, Ingo R., Anil Palaparthi, Karin Cox, Amanda Stark, Lynn Maxfield, and Brian Manternach. "Vocalization with semi-occluded airways is favorable for optimizing sound production." PLOS Computational Biology 17, no. 3 (March 29, 2021): e1008744. http://dx.doi.org/10.1371/journal.pcbi.1008744.
Full textAbstract:
Vocalization in mammals, birds, reptiles, and amphibians occurs with airways that have wide openings to free-space for efficient sound radiation, but sound is also produced with occluded or semi-occluded airways that have small openings to free-space. It is hypothesized that pressures produced inside the airway with semi-occluded vocalizations have an overall widening effect on the airway. This overall widening then provides more opportunity to produce wide-narrow contrasts along the airway for variation in sound quality and loudness. For human vocalization described here, special emphasis is placed on the epilaryngeal airway, which can be adjusted for optimal aerodynamic power transfer and for optimal acoustic source-airway interaction. The methodology is three-fold, (1) geometric measurement of airway dimensions from CT scans, (2) aerodynamic and acoustic impedance calculation of the airways, and (3) simulation of acoustic signals with a self-oscillating computational model of the sound source and wave propagation.
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Liang, Zhimeng, Chunyi Cui, Kun Meng, Yu Xin, Huafu Pei, and Haijiang Li. "New Analytical Solutions for Longitudinal Vibration of a Floating Pile in Layered Soils with Radial Heterogeneity." Mathematics 8, no. 8 (August 5, 2020): 1294. http://dx.doi.org/10.3390/math8081294.
Full textAbstract:
Based on the theory of wave propagation in three-dimensional (3D) continuum, a new analytical approach for the longitudinal vibration characteristics of a floating pile in layered soils with radial heterogeneity is developed by employing a viscous-type damping model. Firstly, an analytical solution for the longitudinal complex impedance at the pile head is deduced by employing the Laplace transform and complex stiffness technique with the compatibility conditions of the pile and radially inhomogeneous surrounding soil. Secondly, a semi-analytical solution in the time domain is further acquired by using the inverse Fourier transform method. Furthermore, the corresponding analytical solutions are validated through contrasts with previous solutions. Finally, parametric analyses are underway to investigate the effect of radial heterogeneity of surrounding soils on longitudinal vibration characteristics of floating piles. It is indicated that the proposed approach and corresponding solutions can provide a more wide-ranging application than the simple harmonic vibration for longitudinal vibration analysis of a floating pile in soils.
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GATMIRI, B., S. LE PENSE, and P. MAGHOUL. "A MULTI-SCALE SEISMIC RESPONSE OF TWO-DIMENSIONAL SEDIMENTARY VALLEYS DUE TO THE COMBINED EFFECTS OF TOPOGRAPHY AND GEOLOGY." Journal of Multiscale Modelling 03, no. 03 (September 2011): 133–49. http://dx.doi.org/10.1142/s1756973711000455.
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It is well known that the response of a site to seismic excitation depends on the local topographical and geological conditions. The current building codes already take into account unidimensional site effects but ignore complex site effects due to two-dimensional irregular configurations. The aim of this work is to contribute to the establishment of a simple predictive method to estimate site effects. The horizontal ground movements at the surface of sedimentary valleys subjected to SV waves with vertical incidence are calculated by using the HYBRID program, combining finite elements in the near field and boundary elements in the far field (FEM/BEM). A parametric study is conducted to examine the combined effects of topography and geology on the amplification of the response spectrum at various points across the valley. The influence of different parameters is considered, such as filling ratios (from empty to full valleys), impedance contrasts between bedrock and sediments, and dimensions.
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Fountain, David M., and Matthew H. Salisbury. "Seismic properties of rock samples from the Pikwitonei granulite belt – God's Lake domain crustal cross section, Manitoba." Canadian Journal of Earth Sciences 33, no. 5 (May 1, 1996): 757–68. http://dx.doi.org/10.1139/e96-058.
Full textAbstract:
Laboratory measurements of compressional and shear wave velocity to confining pressures of 600 MPa for a suite of representative samples collected from the Pikwitonei granulite belt and God's Lake domain, an Archean crustal cross section in the northwestern Superior Province, provide the basis of comparison of these terranes with the seismic characteristics of Archean lower crust. We found that felsic rocks in the Pikwitonei granulite belt and God's Lake domain, which make up the bulk of these terranes, have a similar average compressional wave velocity of 6.5 km/s at 600 MPa, indicating that felsic rocks show little velocity change across the amphibolite–granulite facies transition. Compressional wave velocities for mafic rocks from each terrane are between 7.1 and 7.3 km/s. Apparent Poisson's ratio ranges from 0.24 to 0.26 and 0.26 to 0.28 for felsic and mafic rocks, respectively. These velocity data compare favorably with data for similar lithologies from the Kapuskasing uplift. Using the relative abundances of the constituent lithologies, the weighted average compressional wave velocities of the God's Lake domain and Pikwitonei granulite belt at 600 MPa are 6.56 and 6.63 km/s, respectively. These values, coupled with velocity distribution functions based on the population statistics and relative abundance for each lithology, show that there is no correspondence between the seismic characteristics of the Pikwitonei granulite belt and typical Archean and Proterozoic lower crust. The average properties of the Pikwitonei granulite belt and God's Lake domain, however, correspond well with typical Archean and Proterozoic middle crust. This suggests that either the Pikwitonei granulite belt represents an extreme felsic end member of Archean lower crust or that the deepest levels of the Superior Province crust are not exposed in the Pikwitonei granulite belt. Similar distribution function diagrams for acoustic impedance show that the Pikwitonei granulite belt is characterized by high acoustic impedance contrasts, but the high-impedance component is low in abundance. If the strong reflections observed under the Pikwitonei granulite belt in recent Lithoprobe surveys are not due to other causes, such as favorably oriented bodies of metamorphosed banded iron formation, diabase, or rock units not exposed in this region but present at depth, then they are caused by surprisingly small volumes of mafic metavolcanic rocks.
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Snieder, R., M. Y. Xie, A. Pica, and A. Tarantola. "Retrieving both the impedance contrast and background velocity: A global strategy for the seismic reflection problem." GEOPHYSICS 54, no. 8 (August 1989): 991–1000. http://dx.doi.org/10.1190/1.1442742.
Full textAbstract:
Recorded seismic reflection waveforms contain information as to the small‐scale variations of impedance and the large‐scale variations of velocity. This information can be retrieved by minimizing the misfit between the recorded waveforms and synthetic seismograms as a function of the model parameters. Because of the different physical characters of the velocity and the impedance, we update these parameters in an alternating fashion, which amounts to a relaxation approach to the minimization of the waveform misfit. As far as the impedance is concerned, this minimization can be performed efficiently using gradient algorithms. For the inversion for seismic velocities, gradient methods do not work nearly as well; therefore, we use different minimization methods for determining impedances and velocities. However, the determination of the impedance and the determination of the velocity are strongly coupled; relaxation is most effective when this coupling is as weak as possible. Weak coupling can be achieved partially by parameterizing the impedances not as a function of depth but as a function of traveltime. A nonlinear, nonlocal method is presented for determining the smooth reference velocity from seismic reflection data. This technique is applied both to synthetic seismograms and to real marine data. In both cases, the velocity information implicitly contained in the curvature of the reflection hyperbolas was fully retrieved using nonlinear waveform optimization. In this way, it is possible to reconstruct both the impedance contrast and the smooth reference velocity from band‐limited seismic reflection data using a single waveform‐fit criterion.
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Johansen, Ståle, Espen Granberg, Donatella Mellere, Børge Arntsen, and Torben Olsen. "Decoupling of seismic reflectors and stratigraphic timelines: A modeling study of Tertiary strata from Svalbard." GEOPHYSICS 72, no. 5 (September 2007): SM273—SM280. http://dx.doi.org/10.1190/1.2759479.
Full textAbstract:
In sequence stratigraphic interpretations, the key premise is that stratal surfaces effectively represent geologic timelines. When applied to seismic sections, the fundamental assumption is that primary reflections generally mimic stratigraphic timelines. The main objective of this study was to test how well key reflectors in a seismic section couple to timelines. To achieve the high level of ground control needed for such testing, we combined photogrammetry and traditional sedimentologic fieldwork to optimize the geologic model. We relied further on petrophysical analysis to derive a numerical model suitable for the simulation of seismic data. In spite of laterally discontinuous vertical-impedance contrasts (VICs), false seismic continuity was created, and we observed frequent decoupling of seismic reflectors and stratigraphic timelines. These observations demonstrate how the low-frequency seismic method fails to image normal complexity in a stratigraphic unit. A seismic correlation test showed that the interpreters made numerous mistakes and that such mistakes are very difficult to avoid. The failure of a fundamental assumption, as illustrated here, creates serious problems for the sequence stratigraphic concept when applied to detailed correlation analysis on seismic sections.
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Gómez, Julián L., and Claudia L. Ravazzoli. "Reflection characteristics of linear carbon dioxide transition layers." GEOPHYSICS 77, no. 3 (May 1, 2012): D75—D83. http://dx.doi.org/10.1190/geo2011-0428.1.
Full textAbstract:
Seismic monitoring of underground [Formula: see text] accumulations is a subject of growing interest in applied geophysics. Due to their large impedance contrasts, attention is focused on accumulations of high [Formula: see text] saturation in most cases. However, low-saturation zones with dispersed carbon dioxide, or saturation transition layers, may have an important role in the propagation of waves within the reservoir, giving rise to amplitude and phase changes of the seismic signals. With this motivation, we studied the reflectivity response of a simple reservoir model with a given [Formula: see text] saturation-depth profile, on a theoretical basis. We investigated the influence of the overall saturation, vertical extent, and spatial fluid distribution of a carbon dioxide transition zone in the reflectivity of a reservoir. The parametric analysis entails the computation of the generalized P-wave reflection coefficient and its variations with ray angle (AVA) and frequency (AVF). The combined analysis of AVA and AVF can help to characterize and monitor [Formula: see text] transition layers within geological storage sites.
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Jarchow, Craig M., Rufus D. Catchings, and William J. Lutter. "Large‐explosive source, wide‐recording aperture, seismic profiling on the Columbia Plateau, Washington." GEOPHYSICS 59, no. 2 (February 1994): 259–71. http://dx.doi.org/10.1190/1.1443588.
Full textAbstract:
Clear subsurface seismic images have been obtained at low cost on the Columbia Plateau, Washington. The Columbia Plateau is perhaps the most notorious of all “bad‐data” areas because large impedance contrasts in surface flood basalts severely degrade the seismic wavefield. This degradation was mitigated in this study via a large‐explosive source, wide‐recording aperture shooting method. The shooting method emphasizes the wide‐angle portion of the wavefield, where Fermat’s principle guarantees reverberation will not interfere with the seismic manifestations of crucial geologic interfaces. The basalt diving wave, normally discarded in standard common midpoint (CMP) seismic profiling, can be used to image basalt velocity structure via traveltime inversion. Maximum depth‐penetration of the diving wave tightly constrains basalt‐sediment interface depth. An arrival observed only at shot‐receiver offsets greater than 15 km can be used to determine the velocity and geometry of basement via simultaneous inversion. The results from this study suggest that previous geologic hypotheses and hydrocarbon play concepts for the Columbia Plateau may have been in error.
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Peng, Suping, Huajing Chen, Ruizhao Yang, Yunfeng Gao, and Xinping Chen. "Factors facilitating or limiting the use of AVO for coal-bed methane." GEOPHYSICS 71, no. 4 (July 2006): C49—C56. http://dx.doi.org/10.1190/1.2217137.
Full textAbstract:
There are similarities and differences in employing amplitude variation with offset (AVO) to explore for gas-sand reservoirs, as opposed to coal-bed methane (CBM) reservoirs. The main similarity is that large Poisson’s ratio contrasts, resulting in AVO gradient anomalies, are expected for both kinds of reservoirs. The main difference is that cleating and fracturing raise the Poisson’s ratio of a coal seam as it improves its reservoir potential for CBM, while gas always lowers the Poisson’s ratio of a sandstone reservoir. The top of gas sands usually has a negative AVO gradient, leading to a class one, two, or three anomaly depending on the impedance contrast with the overlying caprock. On the other hand, the top of a CBM reservoir has a positive AVO gradient, leading to a class four anomaly. Three environmental factors may limit the usage of AVO for CBM reservoirs: the smaller contrast in Poisson’s ratio between a CBM reservoir and its surrounding rock, variations in the caprock of a specific CBM reservoir, and the fact that CBM is not always free to collect at structurally high points in the reservoir. However, other factors work in favor of using AVO. The strikingly high reflection amplitude of coal improves signal/noise ratio and hence the reliability of AVO measurements. The relatively simple characteristics of AVO anomalies make them easy to interpret. Because faults are known to improve the quality of CBM reservoirs, faults accompanied by AVO anomalies would be especially convincing. A 3D-AVO example offered in this paper shows that AVO might be helpful to delineate methane-rich sweet spots within coal seams.