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.

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.

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.

Analysis of grid operation state based on improved maximum eigenvalue sample covariance matrix algorithm

2021 ◽  
pp. 095965182110012
Author(s):  
Dinghui Wu ◽  
Juan Zhang ◽  
Bo Wang ◽  
Tinglong Pan
Keyword(s):  
Covariance Matrix ◽  
Signal To Noise Ratio ◽  
Poor Performance ◽  
Sample Covariance Matrix ◽  
Maximum Eigenvalue ◽  
Signal To Noise ◽  
Matrix Algorithm ◽  
Sample Covariance ◽  
Noise Ratio ◽  
Application Fields

Traditional static threshold–based state analysis methods can be applied to specific signal-to-noise ratio situations but may present poor performance in the presence of large sizes and complexity of power system. In this article, an improved maximum eigenvalue sample covariance matrix algorithm is proposed, where a Marchenko–Pastur law–based dynamic threshold is introduced by taking all the eigenvalues exceeding the supremum into account for different signal-to-noise ratio situations, to improve the calculation efficiency and widen the application fields of existing methods. The comparison analysis based on IEEE 39-Bus system shows that the proposed algorithm outperforms the existing solutions in terms of calculation speed, anti-interference ability, and universality to different signal-to-noise ratio situations.

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.

scholarly journals Towards standardized processing of eddy covariance flux measurements of carbonyl sulfide

2019 ◽  
Author(s):  
Kukka-Maaria Kohonen ◽  
Pasi Kolari ◽  
Linda M. J. Kooijmans ◽  
Huilin Chen ◽  
Ulli Seibt ◽  
...  
Keyword(s):  
Data Processing ◽  
Eddy Covariance ◽  
Signal To Noise Ratio ◽  
Carbonyl Sulfide ◽  
Lag Time ◽  
Maximum Effect ◽  
Signal To Noise ◽  
Flux Data ◽  
Flux Measurements ◽  
Noise Ratio

Abstract. Carbonyl sulfide (COS) flux measurements with the eddy covariance (EC) technique are growing in popularity with the recent development in using COS to estimate gross photosynthesis at the ecosystem scale. Flux data intercomparison would benefit from standardized protocols for COS flux data processing. In this study, we analyze how various data processing steps affect the final flux and provide a method for gap-filling COS fluxes. Different methods for determining the lag time between COS mixing ratio and the vertical wind velocity (w) resulted in a maximum of 12 % difference in the cumulative COS flux. Due to limited COS measurement precision, small COS fluxes (below approximately 3 pmol m−2 s−1) could not be detected when the lag time was determined from maximizing the covariance between COS and w. We recommend using a combination of COS and carbon dioxide (CO2) lag times in determining the COS flux, depending on the flux magnitude compared to the detection limit of each averaging period. Different high frequency spectral corrections had a maximum effect of 10 % on COS flux calculations and different detrending methods only 1.2 %. Relative total uncertainty was more than five times higher for low COS fluxes (absolute flux lower than 3 pmol m−2 s−1) than for low CO2 fluxes (lower than 1.5 μmol m−2 s−1), indicating a low signal-to-noise ratio of COS fluxes. Due to similarities in ecosystem COS and CO2 exchange, and the low signal-to-noise ratio of COS fluxes that is similar to methane, we recommend a combination of CO2 and methane flux processing protocols for COS EC fluxes.

Long-period seafloor seismology and deformation under ocean waves

1999 ◽  
Vol 89 (6) ◽  
pp. 1535-1542 ◽  
Author(s):  
Spahr C. Webb ◽  
Wayne C. Crawford
Keyword(s):  
Shallow Water ◽  
Signal To Noise Ratio ◽  
Wave Spectrum ◽  
Vertical Component ◽  
Ocean Waves ◽  
Vertical Acceleration ◽  
Noise Levels ◽  
Signal To Noise ◽  
Long Period ◽  
Noise Ratio

Abstract The deformation of the seafloor under loading by long-period ocean waves raises vertical component noise levels at the deep seafloor by 20 to 30 dB above noise levels at good continental sites in the band from 0.001 to 0.04 Hz. This noise substantially limits the detection threshold and signal-to-noise ratio for long-period phases of earthquakes observed by seafloor seismometers. Borehole installation significantly improves the signal-to-noise ratio only if the sensor is installed at more than 1 km below the seafloor because the deformation signal decays slowly with depth. However, the vertical-component deformation signal can be predicted and suppressed using seafloor measurements of pressure fluctuations observed by differential pressure gauges. The pressure observations of ocean waves are combined with measurements of the transfer function between vertical acceleration and pressure to predict the vertical component deformation signal. Subtracting the predicted deformation signal from pressure observations can reduce vertical component noise levels near 0.01 Hz by more than 25 dB, significantly improving signal-to-noise ratios for long-period phases. There is also a horizontal-component deformation signal but it is smaller than the vertical-component signal and only significant in shallow water (<1-km deep). The amplitude of the deformation signal depends both on the long-period ocean-wave spectrum and the elastic-wave velocities in the oceanic crust. It is largest at sedimented sites and in shallow water.

A comparison of streamer and OBC seismic data at Beryl Alpha field, U. K. North Sea

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. B69-B80 ◽  
Author(s):  
Jonathan Stewart ◽  
Andrew Shatilo ◽  
Charlie Jing ◽  
Tommie Rape ◽  
Richard Duren ◽  
...  
Keyword(s):  
North Sea ◽  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Vertical Component ◽  
Hard Water ◽  
Detailed Comparison ◽  
P Wave ◽  
Data Sets ◽  
Ocean Bottom ◽  
Streamer Data

Compressional P-wave ocean-bottom-cable (OBC) seismic data from the Beryl Alpha field in the U. K. North Sea provide a superior image of the subsurface compared to heritage streamer seismic data. To determine the reason for the superiority of OBC data, the results of a detailed comparison of these OBC and streamer data sets are compared. The streamer and OBC data sets are reprocessed using a strategy that attempts to isolate the roles of processing, fold, azimuth, PZ combination, and hydrophone and geophone data have on the improved OBC image. The vertical component of the geophone (OBC Z) provides the major contribution to the improved OBC image. The imaged OBC Z datacontain fewer multiples and have a higher signal-to-noise ratio than the streamer. The OBC data have a lower level of multiple contamination because of the contribution from the OBC Z component, together with an effective suppression of receiver-side water-column reverberations as a result of the combination of the OBC hydrophone and geophone traces (PZ combination). The increased fold and wider azimuths of OBC data improve the OBC image slightly. Wider azimuths improve fault imaging, especially for faults oriented obliquely to the inline and crossline directions. The particular conditions at Beryl Alpha field that make the OBC survey successful are the relatively hard water bottom and the presence of multiples that are difficult to remove from streamer data using standard demultiple techniques.

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