HORIZONTAL AND VERTICAL ARRAYS FOR TELESEISMIC SIGNAL ENHANCEMENT

Geophysics ◽  
1965 ◽  
Vol 30 (4) ◽  
pp. 597-608 ◽  
Author(s):  
Robert B. Roden
Keyword(s):  
Surface Mode ◽  
Propagation Theory ◽  
Vertical Array ◽  
Signal To Noise ◽  
Coherent Noise ◽  
Maximum Dimension ◽  
Uncorrelated Noise ◽  
Vertical Arrays ◽  
Theoretical Results ◽  
Incoherent Noise

A model of teleseismic signal and surface‐mode noise is derived from wave‐propagation theory. Optimum Wiener multichannel frequency domain filters are designed to operate on the outputs of six seismometer arrays so as to pass signals and reject noise. The arrays studied include two 19‐element surface arrays, two 19‐element shallow‐buried arrays and two 6‐element vertical arrays where a 20‐db reduction in spatially uncorrelated noise is assumed to result from seismometer burial. It is found that there is very little difference among the outputs of the filter systems designed for the two surface arrays and the two vertical arrays. The performance of the systems designed for the shallow‐buried arrays found to be considerably better. For one particular array, the predicted signal‐to‐noise improvement resulting from the assumed effect of shallow burial varies from 5 to 15 db. The theoretical results are sensitive to the amount of uncorrelated noise assumed in the model. However, when the levels of incoherent noise are equal, it appears that a surface array will generally possess greater capability for rejection of coherent noise than will a vertical array with the same size and number of receivers. The performance of an array of either type appears to be quite insensitive to changes of geometry if the number of receivers and the maximum dimension are not changed very much. Although a vertical array will always be superior to a single deeply buried seismometer, the improvement in performance which may be obtained by increasing the number of receivers in a vertical array is much less than in the case of a surface array.

SOME DATA PROCESSING RESULTS FOR A VERTICAL ARRAY OF TRIAXIAL SEISMOMETERS

Geophysics ◽  
1970 ◽  
Vol 35 (2) ◽  
pp. 337-343 ◽  
Author(s):  
Zoltan A. Der
Keyword(s):  
Data Processing ◽  
Signal To Noise Ratio ◽  
Vertical Component ◽  
Poor Performance ◽  
P Wave ◽  
Oil Well ◽  
Vertical Array ◽  
Signal To Noise ◽  
Vertical Arrays ◽  
Three Components

A vertical array of three component (triaxial) seismometers was operated in an abandoned oil well near Grapevine, Texas. The experiment was designed to investigate the effectiveness of teleseismic P‐wave enhancement by utilization of all three components of motion at various depths within the well. Previous experiments with vertical arrays which only recorded the vertical component of motion showed that optimum processors did not significantly improve the signal‐to‐noise ratio (Roden, 1968). The reason for this poor performance was found to be a similarity in the changes of signal and noise properties with depth.

THE VERTICAL ARRAY IN REFLECTION SEISMOLOGY—SOME EXPERIMENTAL STUDIES

Geophysics ◽  
1976 ◽  
Vol 41 (2) ◽  
pp. 219-232 ◽  
Author(s):  
Paul C. Wuenschel
Keyword(s):  
Field Test ◽  
Signal To Noise Ratio ◽  
Experimental Studies ◽  
Seismic Energy ◽  
Reflection Seismology ◽  
Vertical Array ◽  
Signal To Noise ◽  
Near Surface ◽  
Vertical Arrays ◽  
Reflected Signal

There are several advantages in using vertical arrays for recording reflected signal. Signal‐to‐noise ratio can be controlled to any desired level when the noise is due to scattering from layers shallower than the depth to the array. By the use of vertical arrays, the band width of useable seismic energy can be increased, events can be properly identified, the signal that eventually produces near surface induced multiples can be measured, as well as the direct pulse radiated from the source and its accompanying ghosts. A field test documents these predictions.

An automatic means to discriminate between earthquakes and quarry blasts

1990 ◽  
Vol 80 (6B) ◽  
pp. 2143-2160
Author(s):  
Michael A. H. Hedlin ◽  
J. Bernard Minster ◽  
John A. Orcutt
Keyword(s):  
Fourier Transform ◽  
Spectral Features ◽  
Single Event ◽  
Vertical Array ◽  
Signal To Noise ◽  
Spectral Character ◽  
Frequency Pattern ◽  
Time Frequency ◽  
Cepstral Analysis ◽  
Double Fourier Transform

Abstract In this article we discuss our efforts to use the NORESS array to discriminate between regional earthquakes and ripple-fired quarry blasts (events that involve a number of subexplosions closely grouped in space and time). The method we describe is an extension of the time versus frequency “pattern-based” discriminant proposed by Hedlin et al. (1989b). At the heart of the discriminant is the observation that ripple-fired events tend to give rise to coda dominated by prominent spectral features that are independent of time and periodic in frequency. This spectral character is generally absent from the coda produced by earthquakes and “single-event” explosions. The discriminant originally proposed by Hedlin et al. (1989b) used data collected at 250 sec−1 by single sensors in the 1987 NRDC network in Kazakhstan, U.S.S.R. We have found that despite the relatively low digitization rate provide by the NORESS array (40 sec−1) we have had good success in our efforts to discriminate between earthquakes and quarry blasts by stacking all vertical array channels to improve signal-to-noise ratios. We describe our efforts to automate the method, so that visual pattern recognition is not required, and to make it less susceptible to spurious time-independent spectral features not originating at the source. In essence, we compute a Fourier transform of the time-frequency matrix and examine the power levels representing energy that is periodic in frequency and independent of time. Since a double Fourier transform is involved, our method can be considered as an extension of “cepstral” analysis (Tribolet, 1979). We have found, however, that our approach is superior since it is cognizant of the time independence of the spectral features of interest. We use earthquakes to define what cepstral power is to be expected in the absence of ripple firing and search for events that violate this limit. The assessment of the likelihood that ripple firing occurred at the source is made automatically by the computer and is based on the extent to which the limit is violated.

ROBUST SVD FILTERING FOR LOW SIGNAL-TO-NOISE RATIO SEISMIC DATA

Geophysics ◽  
2021 ◽  
pp. 1-51
Author(s):  
Chao Wang ◽  
Yun Wang
Keyword(s):  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Singular Values ◽  
New Method ◽  
Signal To Noise ◽  
Coherent Noise ◽  
Edge Preserving ◽  
Singular Vectors ◽  
Reduced Rank ◽  
Noise Ratio

Reduced-rank filtering is a common method for attenuating noise in seismic data. As conventional reduced-rank filtering distinguishes signals from noises only according to singular values, it performs poorly when the signal-to-noise ratio is very low, or when data contain high levels of isolate or coherent noise. Therefore, we developed a novel and robust reduced-rank filtering based on the singular value decomposition in the time-space domain. In this method, noise is recognized and attenuated according to the characteristics of both singular values and singular vectors. The left and right singular vectors corresponding to large singular values are selected firstly. Then, the right singular vectors are classified into different categories according to their curve characteristics, such as jump, pulse, and smooth. Each kind of right singular vector is related to a type of noise or seismic event, and is corrected by using a different filtering technology, such as mean filtering, edge-preserving smoothing or edge-preserving median filtering. The left singular vectors are also corrected by using the filtering methods based on frequency attributes like main-frequency and frequency bandwidth. To process seismic data containing a variety of events, local data are extracted along the local dip of event. The optimal local dip is identified according to the singular values and singular vectors of the data matrices that are extracted along different trial directions. This new filtering method has been applied to synthetic and field seismic data, and its performance is compared with that of several conventional filtering methods. The results indicate that the new method is more robust for data with a low signal-to-noise ratio, strong isolate noise, or coherent noise. The new method also overcomes the difficulties associated with selecting an optimal rank.

scholarly journals Shielding of Piezoelectric Ultrasonic Probes in Hall Effect Imaging

1998 ◽  
Vol 20 (3) ◽  
pp. 206-220 ◽  
Author(s):  
Han Wen ◽  
Eric Bennett ◽  
David G. Wiesler
Keyword(s):  
Hall Effect ◽  
Electromagnetic Interference ◽  
Thermal Noise ◽  
Signal To Noise Ratio ◽  
High Sensitivity ◽  
Excitation Pulse ◽  
Signal To Noise ◽  
Coherent Noise ◽  
Electrical Pulses ◽  
Coupling Mechanisms

This paper addresses significant sources of electromagnetic noise in Hall effect imaging. Hall effect imaging employs large electrical pulses for signal generation and high sensitivity ultrasonic probes for signal reception. Coherent noise arises through various coupling mechanisms between the excitation pulse and the probe. In this paper, the coupling mechanisms are experimentally isolated and theoretically analyzed. Several methods of shielding the probe from electromagnetic interference are devised and tested. These methods are able to reduce the noise to levels below the random thermal noise, thereby improving the signal-to-noise ratio in HEI by two orders of magnitude.

SEISMIC EXPERIMENTS WITH VERTICAL ARRAYS

Geophysics ◽  
1968 ◽  
Vol 33 (2) ◽  
pp. 270-284 ◽  
Author(s):  
Robert B. Roden
Keyword(s):  
Ambient Noise ◽  
Vertical Component ◽  
P Wave ◽  
Signal Interference ◽  
Vertical Array ◽  
Reflected Waves ◽  
Deep Well ◽  
Vertical Arrays ◽  
Multichannel Filtering ◽  
Selection Of

Experiments with vertical arrays of seismometers were conducted from 1963 to 1965. Data of exceptionally high quality were obtained through the use of special 1‐cps, deep‐well seismometers and direct digital recording techniques. Arrays studied experimentally contained up to 7 vertical‐component seismometers and extended to depths as great as 3.1 km. P‐wave signals observed at depth are generally distorted because of interference between incident and surface‐reflected waves. It is shown that the outputs of two or more deep‐well instruments can be combined to reconstruct signal waveforms. Small additional improvements were obtained through the application of optimum multichannel filtering to vertical array outputs, but the best signal‐to‐noise ratios obtained were never more than 6 db above those available from single deep‐well seismometers located at points of constructive signal interference. Results obtained from analysis of experimental data support the hypothesis that severe attenuation of seismic noise with depth is a characteristic only of sites where ambient noise is very intense at the surface. It is concluded that improvements in record quality which can be obtained through the application of vertical array processing at noisy sites are probably not greater than the improvements which would result from careful selection of a quiet site.

3-D coherency filtering

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1310-1314 ◽  
Author(s):  
Qing Li ◽  
Kris Vasudevan ◽  
Frederick A. Cook
Keyword(s):  
Seismic Data ◽  
Seismic Event ◽  
Signal To Noise Ratio ◽  
Random Noise ◽  
Three Dimensions ◽  
Coherent Noise ◽  
Coherent Signal ◽  
Frequency Space ◽  
Time Space ◽  
Incoherent Noise

Coherency filtering is a tool used commonly in 2-D seismic processing to isolate desired events from noisy data. It assumes that phase‐coherent signal can be separated from background incoherent noise on the basis of coherency estimates, and coherent noise from coherent signal on the basis of different dips. It is achieved by searching for the maximum coherence direction for each data point of a seismic event and enhancing the event along this direction through stacking; it suppresses the incoherent events along other directions. Foundations for a 2-D coherency filtering algorithm were laid out by several researchers (Neidell and Taner, 1971; McMechan, 1983; Leven and Roy‐Chowdhury, 1984; Kong et al., 1985; Milkereit and Spencer, 1989). Milkereit and Spencer (1989) have applied 2-D coherency filtering successfully to 2-D deep crustal seismic data for the improvement of visualization and interpretation. Work on random noise attenuation using frequency‐space or time‐space prediction filters both in two or three dimensions to increase the signal‐to‐noise ratio of the data can be found in geophysical literature (Canales, 1984; Hornbostel, 1991; Abma and Claerbout, 1995).

ENHANCEMENT OF SIGNAL‐TO‐NOISE RATIO IN MAGNETOTELLURIC DATA

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 103-110 ◽  
Author(s):  
Dominic W. Kao ◽  
David Rankin
Keyword(s):  
Confidence Limit ◽  
Signal To Noise Ratio ◽  
Data Selection ◽  
Cyclic Process ◽  
Signal To Noise ◽  
Magnetotelluric Data ◽  
Cyclic Operation ◽  
Noise Ratio ◽  
A New Technique ◽  
Incoherent Noise

A new technique has been developed which can be employed for the enhancement of the signal‐to‐noise ratio of magnetotelluric data and/or for the establishment of a confidence limit as a criterion for final data selection. This technique functions in a consecutively cyclic process which can finally remove the noise from the autopower estimates of MT data if the crosspower estimates are noise free and, consequently, the predicted coherencies can be improved. When noise exists in both autopower and crosspower estimates, the cyclic operation can establish a confidence limit which reveals a direct measure of incoherent noise content and thus is a more reliable criterion than the predicted coherency itself for data selection. The technique is tested using actual MT data and the result shows the adequacy of the technique. It selects useful data from those originally having moderate or low predicted coherencies; thus it appears to be important when the predicted coherency of the majority of the collected data is not high.

Application of frequency-dependent multichannel Wiener filters to detect events in 2D three-component seismometer arrays

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. V133-V141 ◽  
Author(s):  
J. Wang ◽  
F. Tilmann ◽  
R. S. White ◽  
P. Bordoni
Keyword(s):  
Least Squares Method ◽  
Signal To Noise Ratio ◽  
Noise Levels ◽  
Signal To Noise ◽  
Coherent Noise ◽  
Gas Field ◽  
Frequency Dependent ◽  
Wiener Filters ◽  
Noise Ratio

Hydraulic fracture-induced microseismic events in producing oil and gas fields are usually small, and noise levels are high at the surface as a result of the heavy equipment in use. Similarly, in nonhydrocarbon settings, arrays for detecting local earthquakes will benefit from reduced noise levels and the ability to detect smaller events will be increased. We propose a frequency-dependent multichannel Wiener filtering technique with linear constraints that uses an adaptive least-squares method to remove coherent noise in seismic array data. The noise records on several reference channels are used to predict the noise on a primary channel and then can be subtracted from the observed data. On a test with an unconstrained version of this filter, maximal noise suppression leads to signal distortion. Two methods of im-posing constraints then achieve signal preservation. In one case study, synthetic signals are added to noise from a pilot deployment of a hexagonal array (nine three-component seismometers, approximately [Formula: see text]) above a gas field; noise levels are suppressed by up to [Formula: see text] (at [Formula: see text]). In a second case study, natural seismicity recorded at a dense array ([Formula: see text] spacing) in Italy is used, where the application of the filter improves the signal-to-noise ratio (S/N) more than [Formula: see text] (at [Formula: see text]) using 35 stations. In both cases, the performance of the multichannel Wiener filters is significantly better than stacking, espe-cially at lower frequencies where stacking does not help to suppress the coherent noise. The unconstrained version of the filter yields the best improvement in signal-to-noise ratio, but the constrained filter is useful when waveform distortion is unacceptable.

Numerical and Theoretical Study of Concrete Spall Damage under Blast Loads

2014 ◽  
Vol 553 ◽  
pp. 774-779 ◽  
Author(s):  
Jun Li ◽  
Hong Hao
Keyword(s):  
Theoretical Study ◽  
Numerical Study ◽  
Concrete Columns ◽  
Impact Loads ◽  
High Velocity Impact ◽  
Propagation Theory ◽  
Structural Element ◽  
Dynamic Tensile Strength ◽  
Spall Damage ◽  
Theoretical Results

Spall damage is a typical failure mode of concrete structures under blast or high velocity impact loads. At the opposite side from which the structural element was impulsively loaded, spall will occur if the net primary stresses over an area exceed the dynamic tensile strength of concrete. Fragments of structural element could eject with large velocities, and this kind of damage can cause severe threats to equipment and personnel. In the present study, reinforced concrete columns subjected to the blast loading is investigated and the numerical study of concrete spall is conducted. The spall depth is recorded and compared with the theoretical results derived from wave propagation theory. The parameters that affect the concrete spall damage are investigated.

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