Diffraction imaging by multifocusing

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCA75-WCA81 ◽  
Author(s):  
Alex Berkovitch ◽  
Igor Belfer ◽  
Yehuda Hassin ◽  
Evgeny Landa
Keyword(s):  
Radius Of Curvature ◽  
Correct Identification ◽  
Local Velocity ◽  
Large Area ◽  
Seismic Section ◽  
Diffracted Waves ◽  
Diffraction Imaging ◽  
Time Correction ◽  
Two Parameters ◽  
Correlation Procedure

Correct identification of geologic discontinuities, such as faults, pinch-outs, and small-size scattering objects, is a primary challenge of the seismic method. Seismic response from these objects is encoded in diffractions. Our method images local heterogeneities of the subsurface using diffracted seismic events. The method is based on coherent summation of diffracted waves arising in media that include interface discontinuities and local velocity heterogeneities. This is done using a correlation procedure that coherently focuses diffraction energy on a seismic section by flattening diffraction events using a new local-time-correction formula to parameterize diffraction traveltime curves. This time correction, which is based on the multifocusing method, depends on two parameters: the emergent angle and the radius of curvature of the diffracted wavefront. These parameters are estimated directly from prestack seismic traces. The diffraction multifocusing stack (DMFS) can separate diffracted and reflected energy on a stacked section by focusing diffractions to the diffraction location and defocusing the reflection energy over a large area.

Seismic monitoring of diffraction images for detection of local heterogeneities

Geophysics ◽  
1998 ◽  
Vol 63 (3) ◽  
pp. 1093-1100 ◽  
Author(s):  
Evgeny Landa ◽  
Shemer Keydar
Keyword(s):  
Seismic Signal ◽  
Seismic Monitoring ◽  
Surface Velocity ◽  
Radius Of Curvature ◽  
Seismic Section ◽  
Near Surface ◽  
Geological Processes ◽  
Diffracted Waves ◽  
The Media ◽  
Time Correction

Diffracted waves contain valuable information regarding both the structure and composition of the media they are in. In seismic data processing, however, these waves are usually regarded as noise. In this paper, we present an attempt to use scattered/diffracted waves for the detection of local heterogeneities. The method is based on the detection of diffracted waves by concentrating the signal amplitudes from diffracting points on the seismic section. This is done using a correlation procedure that enhances the amplitude of the seismic signal at the location of the diffractors on the common‐diffraction‐point section (D-section). The new local time correction for diffraction traveltime curve parameterization is based on the radius of curvature of the diffracted wavefront and near‐surface velocity. We use the idea of seismic monitoring for detection and delineating local objects which may occur within the subsurface resulting from human activity or fast geological processes. The method consists of continuous repetition of seismic experiments above an investigated area, constructing D-sections, and comparing the images obtained.

Diffraction imaging by focusing‐defocusing: An outlook on seismic superresolution

Geophysics ◽  
2004 ◽  
Vol 69 (6) ◽  
pp. 1478-1490 ◽  
Author(s):  
V. Khaidukov ◽  
E. Landa ◽  
T. J. Moser
Keyword(s):  
Image Resolution ◽  
Correct Identification ◽  
Structural Elements ◽  
Large Area ◽  
Specular Reflections ◽  
Full Wave ◽  
Geological Discontinuities ◽  
Diffraction Imaging ◽  
And Migration ◽  
Traditional Image

Diffractions always need more advertising. It is true that conventional seismic processing and migration are usually successful in using specular reflections to estimate subsurface velocities and reconstruct the geometry and strength of continuous and pronounced reflectors. However, correct identification of geological discontinuities, such as faults, pinch‐outs, and small‐size scattering objects, is one of the main objectives of seismic interpretation. The seismic response from these structural elements is encoded in diffractions, and diffractions are essentially lost during the conventional processing/migration sequence. Hence, we advocate a diffraction‐based, data‐oriented approach to enhance image resolution—as opposed to the traditional image‐oriented techniques, which operate on the image after processing and migration. Even more: it can be shown that, at least in principle, processing of diffractions can lead to superresolution and the recovery of details smaller than the seismic wavelength. The so‐called reflection stack is capable of effectively separating diffracted and reflected energy on a prestack shot gather by focusing the reflection to a point while the diffraction remains unfocused over a large area. Muting the reflection focus and defocusing the residual wavefield result in a shot gather that contains mostly diffractions. Diffraction imaging applies the classical (isotropic) diffraction stack to these diffraction shot gathers. This focusing‐muting‐defocusing approach can successfully image faults, small‐size scattering objects, and diffracting edges. It can be implemented both in model‐independent and model‐dependent contexts. The resulting diffraction images can greatly assist the interpreter when used as a standard supplement to full‐wave images.

Periodically poled KTA crystal investigated using coherent X-ray beams

2000 ◽  
Vol 33 (4) ◽  
pp. 1149-1153 ◽  
Author(s):  
P. Pernot-Rejmánková ◽  
P. A. Thomas ◽  
P. Cloetens ◽  
F. Lorut ◽  
J. Baruchel ◽  
...  
Keyword(s):  
Phase Difference ◽  
Domain Walls ◽  
Structural Information ◽  
Periodically Poled ◽  
Synchrotron Source ◽  
X Ray ◽  
Diffracted Waves ◽  
Coherent Beams ◽  
Diffraction Imaging ◽  
The Difference

The distribution of inverted ferroelectric domains on the surface and within the bulk of a periodically poled KTA (KTiOAsO4) single crystal has been observed using a simple X-ray diffraction imaging setup which takes advantage of the highly coherent beams available at a third-generation synchrotron source, such as the ESRF. This technique allows one to reveal the phase difference between the waves that are Bragg diffracted from adjacent domainsviafree-space propagation (Fresnel diffraction). The phase difference of the diffracted waves is mainly produced by the difference in phases of the structure factors involved, and contains precise structural information about the nature of the domain walls.

scholarly journals Selection of CVD Diamond Crystals for X-ray Monochromator Applications Using X-ray Diffraction Imaging

Crystals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 396 ◽  
Author(s):  
Stanislav Stoupin ◽  
Thomas Krawczyk ◽  
Zunping Liu ◽  
Carl Franck
Keyword(s):  
Spline Interpolation ◽  
Cvd Diamond ◽  
Effective Radius ◽  
Radius Of Curvature ◽  
X Ray Diffraction ◽  
Average Width ◽  
Rocking Curve ◽  
X Ray ◽  
Single Crystal Diamond ◽  
Diffraction Imaging

A set of 20 single crystal diamond plates synthesized using chemical vapor deposition (CVD) was studied using X-ray diffraction imaging to determine their applicability as side-bounce (single-reflection) Laue monochromators for synchrotron radiation. The crystal plates were of optical grade (as provided by the supplier) with (001) nominal surface orientation. High dislocation density was found for all samples. Distortions in the crystal lattice were quantified for low-index Laue reflections of interests using rocking curve topography. Maps of effective radius of curvature in the scattering plane were calculated using spline interpolation of the rocking curve peak position across the studied plates. For several selected plates, nearly flat regions with large effective radius of curvature were found ( R 0 ≳ 30 - 70 m, some regions as large as 1 × 4 mm 2 ). The average width of the rocking curve for these regions was found to be about 150 μ rad (r.m.s.). These observations suggest that the selected CVD diamond plates could be used as intermediate-bandwidth monochromators refocusing the radiation source to a specific location downstream with close to 1:1 distance ratio.

Cracks Emanating From an Erosion in a Pressurized Autofrettaged Thick-Walled Cylinder—Part II: Erosion Depth and Ellipticity Effects

1998 ◽  
Vol 120 (4) ◽  
pp. 354-358 ◽  
Author(s):  
M. Perl ◽  
C. Levy ◽  
H. Fang
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Radius Of Curvature ◽  
Mode I ◽  
Constant Depth ◽  
Erosion Depth ◽  
Short Cracks ◽  
Order Of Magnitude ◽  
Two Parameters ◽  
Walled Cylinder

In Part I of this paper, the effects of constant depth erosion on the mode I stress intensity factor (SIF) were determined for a crack emanating from the erosion deepest point in a pressurized, autofrettaged, thick-walled cylinder. The erosion geometries investigated included semi-circular erosions and several arc erosions of various radii of curvature. Due to the trends found in that portion of the study, erosion depth and ellipticity are believed to have equally important impact on the SIFs. The present paper delves further into these two parameters using the following configurations: (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, W; and (b) semi-elliptical erosions with ellipticities of d/h = 0.3 – 2.0. Deep cracks are found to be practically unaffected by the erosion, similar to the results presented in Part I of the paper. The effective SIF for relatively short cracks is found to be dramatically enhanced by the stress concentration factor (SCF), which encompasses the depth of the erosion as well as its radius of curvature at the tip. As a result of the increased effective SIF, a significant decrease in the vessel’s fatigue life of up to an order of magnitude may occur.

Streamwise Corners with Curvature Independent of Streamwise Distance

1981 ◽  
Vol 32 (4) ◽  
pp. 319-337
Author(s):  
W.H. Barclay ◽  
A.H. Ridha
Keyword(s):  
Layer Thickness ◽  
Symmetry Plane ◽  
Its Region ◽  
Radius Of Curvature ◽  
Sharp Corner ◽  
Dimensional Boundary ◽  
Two Parameters ◽  
Corner Layer ◽  
Streamwise Distance ◽  
Stream Direction

SummaryA two parameter approximate solution is presented for the flow along a streamwise corner having large, possibly infinite, curvature in its region of transition between the two quarter infinite planes which form its asymptotes. The two parameters are the angle between the asymptotes and a quantity proportional to the ratio of the local two-dimensional boundary layer thickness and the radius of curvature of the corner at the symmetry plane. Relative to the corner of infinite curvature (sharp corner) a finite curvature always tends to modify the solution towards that for a flat plate. This implies that for corner angles less than 180° the corner layer thickness in the symmetry plane is less than that for the sharp corner of the same angle and the shear stress is higher, the converse holding for angles greater than 180°. The flow in planes normal to the free stream direction is rather complex and typically there is a reversal in its direction within the symmetry plane.

scholarly journals Diffraction imaging using geometric-mean reverse time migration and common-reflection surface

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. S355-S364 ◽  
Author(s):  
Jianhang Yin ◽  
Nori Nakata
Keyword(s):  
Geometric Mean ◽  
Critical Role ◽  
Seismic Exploration ◽  
Small Scale ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Diffracted Waves ◽  
Common Reflection Surface ◽  
Diffraction Imaging

Diffracted waves contain a great deal of valuable information about small-scale subsurface structure such as faults, pinch-outs, karsts, and fractures, which are closely related to hydrocarbon accumulation and production. Therefore, diffraction separation and imaging with high spatial resolution play an increasingly critical role in seismic exploration. We have applied the geometric-mean reverse time migration (GmRTM) method to diffracted waves for imaging only subsurface diffractors based on the difference of the wave phenomena between diffracted and reflected waves. Numerical tests prove the advantages of this method on diffraction imaging with higher resolution as well as fewer artifacts compared to conventional RTM even when we only have a small number of receivers. Then, we developed a workflow to extract diffraction information using a fully data-driven method, called common-reflection surface (CRS), before we applied GmRTM. Application of this workflow indicates that GmRTM further improves the quality of the image by combining with the diffraction-separation technique CRS in the data domain.

Efficient wave-equation-based diffraction imaging

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. S389-S399 ◽  
Author(s):  
Dongliang Zhang ◽  
Tong W. Fei ◽  
Constantine Tsingas ◽  
Yi Luo
Keyword(s):  
Wave Equation ◽  
Seismic Waves ◽  
Secondary Sources ◽  
Propagating Waves ◽  
Diffracted Waves ◽  
Diffraction Imaging ◽  
Left And Right ◽  
Zero Offset ◽  
Left Image ◽  
The Right

We have developed an efficient and practical wave-equation-based technique to image subsurface geologic features such as isolated scatterers, reflector edges, fault, fracture zones, and erosion whose information is mainly contained in diffracted waves. This technique has the ability to directly reveal and differentiate important geologic features compared with results obtained using reflected seismic waves. This new technique comprises three steps. First, the source and receiver wavefields are decomposed into left- and right-downgoing propagating waves, respectively. Second, applying the imaging condition to the right-downgoing source and receiver wavefields to generate the so-called right-right image. Similarly, a left-left image is generated. Third, the left-left and right-right images are multiplied sample-by-sample to form the final diffraction-based image. The key idea of this method is based on the fact that any dipping reflector exhibits a particular dip direction, so its subsurface image can exist either in the left-left or the right-right image, but not in both. As a result, the sample-by-sample multiplication of the two images eliminates the reflector images. Alternatively, because diffractions are generated by subsurface geologic features, which act as secondary sources and radiate in all directions, ranging from [Formula: see text] to 90°, their energy can exist in both images. After multiplication of both images, only the diffractors remain, whereas the reflectors are suppressed. Our method is applicable only for diffracting objects that radiate in all directions. An exception occurs when reflectors exhibit zero dip. In such a case, zero-dip reflectors could be present in both images and leak into the final diffractor image. We mitigate this problem in several ways, such as omitting near zero-offset input data, muting vertical-propagation components, or applying an [Formula: see text]-[Formula: see text] filter on the final diffraction image.

A critical analysis on the uncertainty computation in ground-penetrating radar-retrieved dry snow parameters

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. H39-H49
Author(s):  
Federico Di Paolo ◽  
Barbara Cosciotti ◽  
Sebastian E. Lauro ◽  
Elisabetta Mattei ◽  
Elena Pettinelli
Keyword(s):  
Wave Velocity ◽  
Ground Penetrating Radar ◽  
Snow Water Equivalent ◽  
Radar Data ◽  
Published Data ◽  
Physical Parameters ◽  
Large Area ◽  
Essential Information ◽  
Two Parameters ◽  
Ground Penetrating

The use of the ground-penetrating-radar (GPR) technique to estimate snow parameters such as thickness, density, and snow water equivalent (SWE) is particularly promising because it allows for surveying a large area in a relatively short amount of time. However, this application requires an accurate evaluation of the physical parameters retrieved from the radar measurements, which requires estimating each quantity involved in the computation along with its associated uncertainty. Conversely, the uncertainties are rarely reported in GPR snow studies, even if they represent essential information for data comparisons with other techniques such as the snow rod or snow pit methods. Snow parameters can be estimated from radar data as follows: The snow thickness can be computed from two-way traveltime if the snow average wave velocity is known; the snow density can be estimated from wave velocity using an appropriate mixing formula, and SWE can be computed once these two parameters have been calculated. Starting from published data, we have estimated the accuracy achievable by computing the overall uncertainty for each GPR-retrieved snow parameter and evaluated the influence of the different sources of uncertainties. The computation was made for three antenna frequencies (250, 500, and 1000 MHz) and various snow depths (0–5 m). We find that for snow thicknesses of less than 3 m, the main contribution to the uncertainties associated with snow parameters is given by the uncertainty on two-way traveltime estimation, especially for low antenna frequencies. However, for thicker snow depths, other factors such as the uncertainty on the antenna separation affect the overall accuracy and cannot be neglected. Our studies highlight the importance of the uncertaintiy assessment and suggest a rigorous way for their computation in the field of quantitative geophysics.

Bloch's Law for Brief Flashes of Large Angular Subtense

1973 ◽  
Vol 36 (3_suppl) ◽  
pp. 1055-1061 ◽  
Author(s):  
William W. Dawson ◽  
Joseph M. Harrison
Keyword(s):  
Stimulus Duration ◽  
Visual Angle ◽  
Critical Period ◽  
Large Area ◽  
Peak Intensity ◽  
Time Correction ◽  
Angular Subtense ◽  
Linear Intensity

Stimuli which subtended a 61° visual angle were used to measure ΔI against a concentric field at 273 trolands. Peak intensity was adjusted to threshold as the stimulus duration was reduced in steps from 1 sec. to 100 microsec. Data from 10 observers allowed the calculation of a variance measure and a slope constant. Reciprocity held only at very short durations. The critical period for this stimulus was about 1 msec. Large errors may be encountered if linear intensity-time correction techniques like the troland-second are applied to large-area brief flashes.

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