Ellipticity of Rayleigh waves recorded in the Midwest

1977 ◽  
Vol 67 (2) ◽  
pp. 369-382
Author(s):  
John L. Sexton ◽  
A. J. Rudman ◽  
Judson Mead
Keyword(s):  
Local Structure ◽  
Rayleigh Waves ◽  
Signal To Noise Ratio ◽  
Interference Effects ◽  
Signal To Noise ◽  
Period Range ◽  
Model Studies ◽  
Single Station ◽  
Special Value ◽  
The Time Domain

Abstract Measurements of ellipticity of Rayleigh waves recorded in the U.S. Midwest have been examined for azimuth dependence, effects of interference, and repeatability, as well as the hypothesis that a single station may be used to determine local structure. Time- and frequency-domain analyses were performed for each event, with more consistent results from the time-domain method. Results indicate that for the period range of 10 to 50 sec, ellipticity depends primarily upon local structure and does not exhibit significant azimuthal dependence. Most ellipticity values for a given period are repeatable within 5 per cent of other measured values from all source regions, with the greatest deviation being about 10 per cent. The cause of the deviations is attributed to interfering waves and/or poor signal-to-noise ratios. Interference effects result in scatter in ellipticity values. An ellipticity peak in the period range of 18 to 22 sec has variable magnitude for different events, depending upon the amount of interference present and the signal-to-noise ratio. Interference effects also manifest themselves as sharp decreases in group-velocity observations even after filtering. Model studies show that ellipticity peaks can exist, which are due to the layered structure and not necessarily to interference effects. Ellipticity measurements (10- to 50-sec-period range) from a single station are useful for determination of a crustal model for the vicinity of the recording station, but should be used in conjunction with other available geophysical and geological data. Ellipticity measurements are shown to be of special value for model determination in areas with sedimentary layering, a result in agreement with the Boore-Toksöz 1969) study.

Rayleigh waves from high-gain long-period stations: Signal extraction, amplitude determination, and separation of overlapping wave trains

1975 ◽  
Vol 65 (6) ◽  
pp. 1761-1778 ◽  
Author(s):  
Eduard Berg
Keyword(s):  
Rayleigh Waves ◽  
Signal To Noise Ratio ◽  
High Gain ◽  
Clear Separation ◽  
Novaya Zemlya ◽  
Oceanic Surface ◽  
Single Station ◽  
Wave Trains ◽  
Short Time

abstract For a signal-to-noise ratio between 0.2 and 0.1 on the original single-component records, amplitudes for Rayleigh waves over oceanic paths of 155° at station MAT and 98° at station KIP have been determined as 12 mμ and 24 mμ peak-to-peak, respectively, with a standard error of less than 11 per cent. In each case the processed correlation signal is the highest in a half-hour record. The method makes use of preliminary high-pass filtering and normalized reference earthquake-matched filtering, and takes full advantage of the well-dispersed oceanic surface wave. The method also provides high resolution of co-located events with short time separation, or of widely spaced events with Rayleigh waves arriving nearly simultaneously at a single station, when the summed vertical and radial matched filtered components are used. Examples include: (1) clear separation and amplitude determination at stations KIP and MAT of two MS = 6.5 earthquakes located 0.7° and 145 sec apart off the coast of central Chile; (2) clear separation at station KIP of a Novaya Zemlya mb = 4.8 event from interfering Rayleigh waves of an mb = 5.0 Kermadec Island earthquake arriving 120 to 140 sec prior to the searched event, with almost complete elimination of interference on the summed vertical and radial processed components; and (3) clear separation at station KIP of two co-located mb = 4.4 and 4.5 earthquakes 6 min apart off the coast of Chile, with determination of their amplitudes in the presence of interfering Rayleigh waves from two central Alaska earthquakes, the first (mb = 4.1) arriving 15 min prior to the first Chile Rayleigh wave and the second between the two Chile arrivals. The single-station threshold reached (10 and 25 digital units, p-p) for stations MAT and KIP at 155° and 98°, respectively, corresponds to an MS = 3.3 and probably can be improved further.

scholarly journals Evaluation of Nonlinear Interference Effects in a Dispersion Managed (DM) Optical Fiber: Performance and Transmission Analysis of 16QAM Modulation using Split Step Fourier Method

2020 ◽  
Author(s):  
Reinhardt Rading
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Optical Fiber ◽  
Signal To Noise Ratio ◽  
Fourier Method ◽  
Interference Effects ◽  
Signal To Noise ◽  
Optical Links ◽  
Noise Ratio ◽  
The Impact

<div>This paper investigates the impact on the optical</div><div>signal-to-noise ratio (OSNR) of the residual per span (RDPS) in a N × 100km dispersion managed system with zero total accumulated dispersion from input to output using split step Fourier method (SSFM) -Monte Carlo simulation. </div><div><br></div><div>This paper shows that the nonlinear interference NLI does in-fact impact the performance yielding different best working power depending on the value of Nx100 km span and the type of dispersion managed link. The paper shows that dispersion uncompensated optical links are preferable to dispersion managed fibers in equalizing NLI effects in long haul optical links.</div>

Adaptation of Telegraph Diffusion Equation for Noise Reduction on Images

2017 ◽  
Vol 17 (02) ◽  
pp. 1750010 ◽  
Author(s):  
Pandry Koffi Ghislain ◽  
Georges Lausanne Loum ◽  
Ouattara Nouho
Keyword(s):  
Diffusion Equation ◽  
Noise Reduction ◽  
Local Structure ◽  
Signal To Noise Ratio ◽  
Input Image ◽  
Weak Signal ◽  
Signal To Noise ◽  
Reduction Processes ◽  
Fine Structures

The Telegraph Diffusion Equation (TDE) used in some noise reduction processes in an image includes two main parameters: the damping coefficient and the relaxation time. Classically, the first is determined globally for a given input image, while the second one is set constant. In this paper, we propose to determine the values of these parameters according to the information and the image local structure. We then get an adaptive diffusion equation that permits to better control the degree of smoothness and preserve fine structures and image contours avoiding speckles phenomena and staircase. The acquired results show that the proposed method improves the quality of images that have a weak signal-to-noise ratio, comparatively to the methods based on the TDE whose parameters are not adaptive.

Prestack structurally constrained impedance inversion

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. R89-R103 ◽  
Author(s):  
Haitham Hamid ◽  
Adam Pidlisecky ◽  
Larry Lines
Keyword(s):  
Seismic Data ◽  
Local Structure ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Simultaneous Inversion ◽  
Common Depth Point ◽  
Inversion Methods ◽  
Impedance Inversion ◽  
Regularization Operator ◽  
Complex Geology

Classical prestack impedance inversion methods are based on performing a common-depth point (CDP) by CDP inversion using Tikhonov-type regularization. We refer to it as lateral unconstrained inversion (1D-LUI). Prestack seismic data usually have a low signal-to-noise ratio, and the 1D-LUI approach is sensitive to noise. The inversion results can be noisy and lead to an unfocused transition between vertical formation boundaries. The lateral constrained inversion (1D-LCI) can suppress the noise and provide sharp boundaries between inverted 1D models in regions where the layer dips are less than 20°. However, in complex geology, the disadvantage of using the 1D-LC approach is the lateral smearing of the steeply dipping layers. We have developed a structurally constrained inversion (1D-SCI) approach to mitigate the smearing associated with 1D-LCI. SCI involves simultaneous inversion of all seismic CDPs using a regularization operator that forces the solution to honor the local structure. The results of the 1D-SCI were superior compared with the 1D-LUI and 1D-LCI approaches. The steeply dipping layers are clearly visible on the SCI inverted results.

Shear‐wave processing of sonic log waveforms in a limestone reservoir

Geophysics ◽  
1988 ◽  
Vol 53 (5) ◽  
pp. 668-676 ◽  
Author(s):  
David Goldberg ◽  
William T. Gant
Keyword(s):  
Shear Wave ◽  
Rayleigh Waves ◽  
Wave Attenuation ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Signal To Noise ◽  
Sonic Log ◽  
Compositional Changes ◽  
Sonic Logs ◽  
Full Waveforms

Sonic full waveforms were recorded in a shale‐limestone interval with an experimental 12-channel acoustic logging device. Well-defined shear (pseudo‐Rayleigh) waves were observed throughout most of the 142 m interval and were used to distinguish lithologic boundaries and zones of fracturing as interpreted by logs. The high signal‐to‐noise ratio of the waveforms permitted meaningful shear velocities to be obtained by intervals in this well. A correlation of changes in the [Formula: see text] ratio with depth aided in identifying some compositional changes in the well, but such a correlation could not be used to distinguish fracturing in the limestone. Shear‐wave amplitudes, however, were effective for identifying lithologic changes, as well as fractures, from the sonic log. Shear amplitudes were lower in the shale than in the limestone, and shear‐wave attenuation increased in fractured zones. There was no strong correlation between the degree of fracturing and the attenuation of Stoneley waves. In general, shear‐wave processing of sonic logs is recommended for interpretation of lithology and fracturing in any well in which full waveforms are recorded and shear waves propagate.

Effects of the durations of crosscorrelated microtremor records on broadband dispersion measurements using seismic interferometry

Geophysics ◽  
2014 ◽  
Vol 79 (3) ◽  
pp. Q11-Q19 ◽  
Author(s):  
Kosuke Chimoto ◽  
Hiroaki Yamanaka
Keyword(s):  
Time Series ◽  
Power Law ◽  
Signal To Noise Ratio ◽  
Wave Dispersion ◽  
Theoretical Work ◽  
Seismic Interferometry ◽  
Surface Wave Dispersion ◽  
Period Range ◽  
Long Time ◽  
The Time Domain

For ambient noise, a long time series is typically used for measuring surface-wave dispersion in seismic interferometry. It is preferable to measure dispersions with a broad period range. The reliability of such measurements is often studied using the signal-to-noise ratio (S/N) of the crosscorrelation function (CCF). While many studies have revealed that the S/N evolves as the length of a time series increases, the required conditions for such measurements remain unclear. We maximized the period range suitable for dispersion measurements by examining variations in the amplitudes of the signals and noise of CCFs. For these purposes, and to preserve the broadband amplitude information, we do not apply filtering in the frequency domain or signal normalization in the time domain. The preserved signals and the trailing noise levels of the CCFs exhibit different time-varying features that agree with the predictions of theoretical work on amplitudes. Specifically, as the duration of the crosscorrelated time series increases, the amplitude of the signal remains constant while the trailing noise decreases. Moreover, the trailing noise exhibits a power-law dependence on the period. The period range in which the maximum CCF amplitude exceeds the level expected for this power law corresponds to the period range in which dispersion measurements can be made appropriately with frequency-time analysis (FTAN). This approach can be used to quantitatively determine the optimal period range for dispersion measurements. Results obtained with this method indicate that long-duration records used for crosscorrelation provide not only high S/Ns but also broaden the period range in which dispersion measurements can be made.

scholarly journals Reduction of Phase Noise in Interferometry with State-space Analysis

1979 ◽  
Vol 49 ◽  
pp. 103-110
Author(s):  
Ali Okatan ◽  
J. P. Basart
Keyword(s):  
Phase Noise ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
State Space Analysis ◽  
The Common ◽  
The Time Domain ◽  
Fringe Frequency ◽  
Incoherent Averaging ◽  
Averaging Techniques

In radio mapping, one of the problems encountered is the random bias in the visibility estimate. The bias can be divided into two parts: (a) the positive bias due to the common sky background seen by all elements of the interferometer, and (b) the negative bias due to phase noise present in the system. The first kind of bias can be easily removed by subtracting the correlation between the signals at two interferometer sites when the source is not in the antenna beams from that measured with the source in the antenna beams. This bias will therefore not be considered here. In contrast, the second kind of bias is more difficult to remove. When the signal-to-noise ratio of the interferometer system is high, incoherent averaging techniques can be utilized in the fringe frequency or in the time domain (Clark et al., 1969; Moran, 1973).

scholarly journals Evaluation of Nonlinear Interference Effects in a Dispersion Managed (DM) Optical Fiber: Performance and Transmission Analysis of 16QAM Modulation using Split Step Fourier Method

2020 ◽  
Author(s):  
Reinhardt Rading
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Optical Fiber ◽  
Signal To Noise Ratio ◽  
Fourier Method ◽  
Interference Effects ◽  
Signal To Noise ◽  
Optical Links ◽  
Noise Ratio ◽  
The Impact

<div>This paper investigates the impact on the optical</div><div>signal-to-noise ratio (OSNR) of the residual per span (RDPS) in a N × 100km dispersion managed system with zero total accumulated dispersion from input to output using split step Fourier method (SSFM) -Monte Carlo simulation. </div><div><br></div><div>This paper shows that the nonlinear interference NLI does in-fact impact the performance yielding different best working power depending on the value of Nx100 km span and the type of dispersion managed link. The paper shows that dispersion uncompensated optical links are preferable to dispersion managed fibers in equalizing NLI effects in long haul optical links.</div>

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

Experiments in Bright-Field Imaging with Hollow-Cone Illumination

1981 ◽  
Vol 39 ◽  
pp. 226-227
Author(s):  
W. Kunath ◽  
K. Weiss ◽  
E. Zeitler
Keyword(s):  
Signal To Noise Ratio ◽  
Carbon Support ◽  
Electronic System ◽  
Optic Axis ◽  
Hollow Cone ◽  
Signal To Noise ◽  
Bright Field ◽  
Noise Ratio ◽  
Single Field ◽  
Field Imaging

Bright-field images taken with axial illumination show spurious high contrast patterns which obscure details smaller than 15 ° Hollow-cone illumination (HCI), however, reduces this disturbing granulation by statistical superposition and thus improves the signal-to-noise ratio. In this presentation we report on experiments aimed at selecting the proper amount of tilt and defocus for improvement of the signal-to-noise ratio by means of direct observation of the electron images on a TV monitor.Hollow-cone illumination is implemented in our microscope (single field condenser objective, Cs = .5 mm) by an electronic system which rotates the tilted beam about the optic axis. At low rates of revolution (one turn per second or so) a circular motion of the usual granulation in the image of a carbon support film can be observed on the TV monitor. The size of the granular structures and the radius of their orbits depend on both the conical tilt and defocus.

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