Seismic attenuation tomography using the frequency shift method

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 895-905 ◽  
Author(s):  
Youli Quan ◽  
Jerry M. Harris
Keyword(s):  
Frequency Shift ◽  
Low Frequency ◽  
Seismic Signal ◽  
Seismic Attenuation ◽  
Seismic Survey ◽  
Shift Method ◽  
Geometric Spreading ◽  
Frequency Independent ◽  
Q Model ◽  
Frequency Components

We present a method for estimating seismic attenuation based on frequency shift data. In most natural materials, seismic attenuation increases with frequency. The high‐frequency components of the seismic signal are attenuated more rapidly than the low‐frequency components as waves propagate. As a result, the centroid of the signal's spectrum experiences a downshift during propagation. Under the assumption of a frequency‐independent Q model, this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically. The frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation. In comparison to some other methods of estimating attenuation, our frequency shift method is relatively insensitive to geometric spreading, reflection and transmission effects, source and receiver coupling and radiation patterns, and instrument responses. Tests of crosswell attenuation tomography on 1-D and 2-D geological structures are presented.

Quantifying uncertainties in attenuation estimation at methane-hydrate-bearing zones using sonic waveform logs

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. D339-D353 ◽  
Author(s):  
Hiroyuki Suzuki ◽  
Jun Matsushima
Keyword(s):  
Frequency Shift ◽  
Methane Hydrate ◽  
Seismic Attenuation ◽  
Estimation Methods ◽  
Ratio Method ◽  
Median Frequency ◽  
Waveform Data ◽  
Shift Method ◽  
Sonic Logging ◽  
Attenuation Estimation

Application of seismic attenuation estimation using sonic waveform data is limited because the estimation methods have not yet been fully developed. Although the median frequency shift method is considered to be effective and robust compared to the conventional spectral ratio method, we demonstrated that the median frequency shift methods strongly depend on reference data under lower signal-to-noise ratios. We modified an existing median frequency shift method not to depend on arbitrarily choosing a reference value and to quantify the uncertainties in attenuation estimation. Furthermore, we implied the optimum selection of receiver pairs used for more stable attenuation analysis. Our numerical experiments supported the advantage of the proposed method. Although our main findings by applying the proposed methods in methane hydrate-bearing sediments are almost consistent with past field sonic logging measurements, we find some differences in the magnitude of attenuation values compared to existing sonic attenuation measurements and discuss various possible factors. We believe that more stable and reliable attenuation results can lead to clarifying various factors affecting attenuation estimation, such as the effect of scattering, near-field effects, and source-coupling effects. Furthermore, we emphasized the importance of scattering effect caused by the heterogeneity of the formation and demonstrated the limitation of characterizing the 1D heterogeneity using the sonic logging data spatially sampled at 0.15 m to adequately estimate the effect of scattering attenuation.

Robust prestack Q-determination using surface seismic data: Part 1 — Method and synthetic examples

Geophysics ◽  
2012 ◽  
Vol 77 (1) ◽  
pp. R45-R56 ◽  
Author(s):  
Carl Reine ◽  
Roger Clark ◽  
Mirko van der Baan
Keyword(s):  
Reservoir Characterization ◽  
Accurate Determination ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Spectral Interference ◽  
Seismic Survey ◽  
Time Frequency ◽  
Frequency Independent ◽  
Variable Window ◽  
Amplitude Variation With Angle

The accurate determination of seismic attenuation, or [Formula: see text], is useful for signal enhancement and reservoir characterization. To arrive at the necessary accuracy however, a number of issues must be addressed in the measurement technique. Specifically, spectral interference from closely spaced reflections is a major concern, in addition to the assumptions and errors associated with the raypath geometries of the reference and measured reflections. We have developed a robust method for measuring attenuation from prestack surface seismic gathers that helps minimize these issues. In our prestack [Formula: see text]-inversion technique; the presence of spectral interference was first reduced by making use of a variable-window time-frequency transform. To minimize the effects of the remaining interference, we then made use of an inversion scheme operating simultaneously in the frequency and traveltime-difference coordinates. A by-product of this inversion was a collection of the frequency-independent amplitude changes, which in the absence of geometric spreading, contains valuable amplitude variation with angle information, free from attenuation amplitude losses. Furthermore, under the assumption of locally 1D velocity and attenuation distributions, we made use of the [Formula: see text] transform to operate on traces of constant horizontal slowness. This allowed angle-dependent effects in the overburden such as attenuation anisotropy and source or receiver directivity to be eliminated. In the second part of our study, published separately, this technique was also demonstrated upon a shallow 3D seismic survey, and the measurements compared to another Q-estimation technique, as well as measurements from a vertical seismic profile.

Seismic attenuation of Atlantic margin basalts: Observations and modeling

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. B211-B221 ◽  
Author(s):  
Jennifer Maresh ◽  
Robert S. White ◽  
Richard W. Hobbs ◽  
John R. Smallwood
Keyword(s):  
Seismic Energy ◽  
Seismic Signal ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Thin Layers ◽  
Seismic Survey ◽  
Rock Properties ◽  
Intrinsic Attenuation ◽  
High Impedance ◽  
1D Modeling

Paleogene basalts are present over much of the northeastern Atlantic European margin. In regions containing significant thicknesses of layered basalt flows, conducting seismic imaging within and beneath the volcanic section has proven difficult, largely because the basalts severely attenuate and scatter seismic energy. We use data from a vertical seismic profile (VSP) from well 164/07-1 that penetrated [Formula: see text] of basalt in the northern Rockall Trough west of Britain to measure the seismic attenuation caused by the in-situ basalts. The effective quality factor [Formula: see text] of the basalt layer is found from the VSP to be 15–35, which is considerably lower (more attenuative) than the intrinsic attenuation measured on basalt samples in the laboratory. We then run synthetic seismogram models to investigate the likely cause of the attenuation. Full waveform 1D modeling of stacked sequences of lava flows based on rock properties from the same well indicates that much of the seismic attenuation observed from the VSP can be accounted for by the scattering effects of multiple thin layers with high impedance contrasts. Phase-screen seismic modeling of the rugose basalt surface at the top-of-basalt sediment interface, with the magnitude and wavelength of the relief constrained by a 3D seismic survey around the well, suggests that surface scattering from this interface plays a much smaller role than internal scattering in attenuating the seismic signal as it passes through the basalt sequence.

A sparse spectrum technique for gridding and separating potential field anomalies

Geophysics ◽  
2000 ◽  
Vol 65 (4) ◽  
pp. 1154-1161 ◽  
Author(s):  
Fernando Guspí ◽  
Beatriz Introcaso
Keyword(s):  
Fourier Transform ◽  
High Resolution ◽  
Potential Field ◽  
Low Frequency ◽  
Seismic Signal ◽  
Separation Procedure ◽  
Virtual Absence ◽  
Large Matrix ◽  
Frequency Components ◽  
The Difference

The separation of regional and residual potential field anomalies, regarded as a spectral problem, can be greatly facilitated when a spectrum estimate shows a clear break between low‐ and high‐frequency components, a feature that normal fast‐Fourier‐transform (FFT) methods fail to present. In this work, we model the discrete Fourier transform of a potential field, measured at stations irregularly distributed on a surface, by means of a high‐resolution sparse estimate derived originally for seismic signal processing. The coefficients of this estimate, which are distributed according to the Cauchy probability law, produce a model with only few components having a significant value. A steepest‐descent algorithm gives a computing alternative to large matrix multiplications and inversions. Advantages of taking this approach are twofold. First, the high‐resolution transform can be used as a gridding tool to evaluate the potential field either on a horizontal plane or on the topographic surface. The enhancement of the spectral peaks and the virtual absence of sidelobes prevents oscillations and edge effects in the result. Secondly, the sparse distribution of the spectral elements allows the interpreter to locate clearly the low‐frequency components related to the regional field. After a second and faster pass, the values of those coefficients can be redefined in order to obtain a more robust separation, ajusting the residuals by the Cauchy criterion. A theoretical noise‐free example to separate the magnetic anomaly of a prism from a polynomial background illustrates well the difference between sparse and FFT spectra. An example with real Bouguer anomalies in the Interserrana basin, Argentina, shows that gridding results, in this case reduced to sea level, compare well with those obtained by other gridding methods, and that the separation procedure is able to outline well defined areas of positive and negative residual anomalies.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

ANALYSIS OF STAND RESEARCH RESULTS OF AXIAL DYNAMIC FORCE IN DRILLING BY THREE ROLLER CONE BIT

2019 ◽  
pp. 81-93
Author(s):  
В. М. Мойсишин ◽  
M. V. Lyskanych ◽  
R. A. Zhovniruk ◽  
Ye. P. Majkovych
Keyword(s):  
Low Frequency ◽  
Maximum Energy ◽  
Dynamic Force ◽  
Low Frequency Oscillation ◽  
Drilling Tool ◽  
Rock Destruction ◽  
Frequency Components ◽  
Harmonic Components ◽  
Experimental Values ◽  
Harmful Effects

The purpose of the proposed article is to establish the causes of oscillations of drilling tool and the basic laws of the distribution of the total energy of the process of changing the axial dynamic force over frequencies of spectrum. Variable factors during experiments on the classical plan were the rigidity of drilling tool and the hardness of the rock. According to the results of research, the main power of the process of change of axial dynamic force during drilling of three roller cone bits is in the frequency range 0-32 Hz in which three harmonic frequency components are allocated which correspond to the theoretical values of low-frequency and gear oscillations of the chisel and proper oscillations of the bit. The experimental values of frequencies of harmonic components of energy and normalized spectrum as well as the magnitude of the dispersion of the axial dynamic force and its normalized values at these frequencies are presented. It has been found that with decreasing rigidity of the drilling tool maximum energy of axial dynamic force moves from the low-frequency oscillation region to the tooth oscillation area, intensifying the process of rock destruction and, at the same time, protecting the tool from the harmful effects of the vibrations of the bit. Reducing the rigidity of the drilling tool protects the bit from the harmful effects of the vibrations generated by the stand. The energy reductions in these fluctuations range from 47 to 77%.

A Novel Adaptive PET/CT Image Fusion Algorithm

2019 ◽  
Vol 14 (7) ◽  
pp. 658-666
Author(s):  
Kai-jian Xia ◽  
Jian-qiang Wang ◽  
Jian Cai
Keyword(s):  
Lung Cancer ◽  
Image Fusion ◽  
High Frequency ◽  
Malignant Tumors ◽  
Low Frequency ◽  
Combination Method ◽  
Ct Image ◽  
Fusion Algorithm ◽  
Pet Ct ◽  
Frequency Components

Background: Lung cancer is one of the common malignant tumors. The successful diagnosis of lung cancer depends on the accuracy of the image obtained from medical imaging modalities. Objective: The fusion of CT and PET is combining the complimentary and redundant information both images and can increase the ease of perception. Since the existing fusion method sare not perfect enough, and the fusion effect remains to be improved, the paper proposes a novel method called adaptive PET/CT fusion for lung cancer in Piella framework. Methods: This algorithm firstly adopted the DTCWT to decompose the PET and CT images into different components, respectively. In accordance with the characteristics of low-frequency and high-frequency components and the features of PET and CT image, 5 membership functions are used as a combination method so as to determine the fusion weight for low-frequency components. In order to fuse different high-frequency components, we select the energy difference of decomposition coefficients as the match measure, and the local energy as the activity measure; in addition, the decision factor is also determined for the high-frequency components. Results: The proposed method is compared with some of the pixel-level spatial domain image fusion algorithms. The experimental results show that our proposed algorithm is feasible and effective. Conclusion: Our proposed algorithm can better retain and protrude the lesions edge information and the texture information of lesions in the image fusion.

Underwater Image Enhancement Method Combining color and Luminance

2020 ◽  
Vol 13 ◽  
Author(s):  
ZHAO Baiting ◽  
WANG Feng ◽  
JIA Xiaofen ◽  
GUO Yongcun ◽  
WANG Chengjun
Keyword(s):  
Image Enhancement ◽  
Color Space ◽  
Low Frequency ◽  
Brightness Enhancement ◽  
Color Distortion ◽  
Underwater Image ◽  
Enhancement Method ◽  
Frequency Components ◽  
Image Contour ◽  
Objective Indicators

Background:: Aiming at the problems of color distortion, low clarity and poor visibility of underwater image caused by complex underwater environment, a wavelet fusion method UIPWF for underwater image enhancement is proposed. Methods:: First of all, an improved NCB color balance method is designed to identify and cut the abnormal pixels, and balance the color of R, G and B channels by affine transformation. Then, the color correction map is converted to CIELab color space, and the L component is equalized with contrast limited adaptive histogram to obtain the brightness enhancement map. Finally, different fusion rules are designed for low-frequency and high-frequency components, the pixel level wavelet fusion of color balance image and brightness enhancement image is realized to improve the edge detail contrast on the basis of protecting the underwater image contour. Results:: The experiments demonstrate that compared with the existing underwater image processing methods, UIPWF is highly effective in the underwater image enhancement task, improves the objective indicators greatly, and produces visually pleasing enhancement images with clear edges and reasonable color information. Conclusion:: The UIPWF method can effectively mitigate the color distortion, improve the clarity and contrast, which is applicable for underwater image enhancement in different environments.

Despeckling of Sar Images Using Shrinkage of Two-Dimensional Discrete Orthonormal S-Transform

2020 ◽  
pp. 2150023
Author(s):  
Priya R. Kamath ◽  
Kedarnath Senapati ◽  
P. Jidesh
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Relevant Information ◽  
Detection Algorithm ◽  
Two Dimensional ◽  
Sar Images ◽  
S Transform ◽  
Processing Step ◽  
Frequency Components ◽  
Shock Filter

Speckles are inherent to SAR. They hide and undermine several relevant information contained in the SAR images. In this paper, a despeckling algorithm using the shrinkage of two-dimensional discrete orthonormal S-transform (2D-DOST) coefficients in the transform domain along with shock filter is proposed. Also, an attempt has been made as a post-processing step to preserve the edges and other details while removing the speckle. The proposed strategy involves decomposing the SAR image into low and high-frequency components and processing them separately. A shock filter is used to smooth out the small variations in low-frequency components, and the high-frequency components are treated with a shrinkage of 2D-DOST coefficients. The edges, for enhancement, are detected using a ratio-based edge detection algorithm. The proposed method is tested, verified, and compared with some well-known models on C-band and X-band SAR images. A detailed experimental analysis is illustrated.

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