Comparison of Some Theoretical Noise Models with the NORSOR Microseismic Noise Field PDF Download
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Author: Eivind Rygg
Publisher:
ISBN:
Category :
Languages : en
Pages : 24
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The effectiveness of large arrays in mapping the noise field is well known. The paper describes an attempt to estimate the noise field by using a small number of sensors. The noise fields are defined by their power densities in the frequency-wavenumber space and their validity will be judged by comparing coherence estimates of real data with coherence computations on the basis of the models. The real data-base have been recordings from Oyer array - the first large installation in the NORSAR area. (Author).
Author: Eivind Rygg
Publisher:
ISBN:
Category :
Languages : en
Pages : 24
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Book Description
The effectiveness of large arrays in mapping the noise field is well known. The paper describes an attempt to estimate the noise field by using a small number of sensors. The noise fields are defined by their power densities in the frequency-wavenumber space and their validity will be judged by comparing coherence estimates of real data with coherence computations on the basis of the models. The real data-base have been recordings from Oyer array - the first large installation in the NORSAR area. (Author).
Author: Eivind Rygg
Publisher:
ISBN:
Category : Microseisms
Languages : en
Pages : 28
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Author:
Publisher:
ISBN:
Category : Technology
Languages : en
Pages : 188
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Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 194
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Author: Abdullatif Al-Shuhail
Publisher: Springer Nature
ISBN: 3030329488
Category : Technology & Engineering
Languages : en
Pages : 190
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Book Description
This book examines the effects of incoherent noise and how it leads to the misinterpretation of seismic data. It also reviews common noise reduction approaches and their drawbacks, focusing on developments that have occurred in the past decade. The main features of this book include: • Hands-on implementation in MATLAB and/or C • In-depth discussions of both theoretical and practical aspects of the subject • Supplementary, real-world seismic data • Detailed descriptions of structure-enhancing filters. Connecting the theory and practical implementation of noise reduction, the book helps readers fill the gap from equations to code, and from classical filters to the preservation and enhancement of a robust structure. Lastly, it highlights cutting-edge research in the area. As such, it is of interest to researchers in the fields of petroleum engineering, exploration seismology, and geophysics, as well as to practitioners working in the petroleum industry.
Author: Christopher R. Bradley
Publisher:
ISBN:
Category : Microseisms
Languages : en
Pages : 490
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Book Description
Ambient noise in the sea has been observed for over 100 years. Previous studies conclude that the primary source of microseisms is nonlinear interaction of surface gravity waves at the sea surface. Though this source relationship is generally accepted, the actual processes by which the wave generated acoustic noise in the water column couples and propagates to and along the sea floor are not well understood. In this thesis, the sources and propagation of sea floor and sub-sea floor microseismic noise between 0.2 and 10 Hz are investigated. This thesis involves a combination of theoretical, observational and numerical analysis to probe the nature of the microseismic field in the Blake Bahama Basin. Surface waves are the primary mechanism for noise propagation in the crust and fall into two separate groups depending on the relative wavelength/water depth ratio. Asymptotic analysis of the Sommerfeld integral in the complex ray parameter plane shows results that agree with previous findings by Strick (1959) and reveal two fundamental interface wave modes for short wavelength noise propagation in the crust: the Stoneley and pseudo-Rayleigh wave. For ocean sediments, where the shear wave velocity is less than the acoustic wave velocity of water, only the Stoneley interface wave can exist. For well consolidated sediments and basalt, the shear velocity exceeds the acoustic wave velocity of water and the pseudo-Rayleigh wave can also exist. Both interface waves propagate with retrograde elliptic motion at the sea floor and attenuate with depth into the crust, however the pseudo-Rayleigh wave travels along the interface with dispersion and attenuation and "leaks" energy into the water column for a half-space ocean over elastic crust model. For finite depth ocean models, the pseudo-Rayleigh wave is no longer leaky and approaches the Rayleigh wave velocity of the crust. The analysis shows that longer wavelength noise propagates as Rayleigh and Stoneley modes of the ocean+crust waveguide. These long wavelength modes are the fundamental mechanism for long range noise propagation. During the Low Frequency Acoustic Seismic Experiment (LFASE) a four-node, 12- channel borehole array (SEABASS) was deployed in the Blake Bahama Basin off the coast of eastern Florida (DSDP Hole 534B). This experiment is unique and is the first use of a borehole array to measure microseismic noise below the sea floor. Ambient background noise from a one week period is compared between an Ocean Bottom Seismometer (OBS) and SEABASS at sub-bottom depths of 10, 40, 70 and 100 meters below the sea floor. The 0.3 H z microseism peak is found to be nearly invariant with depth and has a power level of 65 and 75 dB rel 1 (nm/ s2)2)/ H z for the vertical and horizontal components respectively. At 100 m depth, the mean microseismic noise levels above 0.7 Hz are 10 dB and 15-20 dB quieter for the vertical and horizontal components respectively. Most of this attenuation occurs in the upper 10 m above 1.0 Hz, however higher modes in the spectra show narrow bandwidth variability in the noise field that is not monotonic with depth. Dispersion calculations show normal mode Stoneley waves below 0.7 Hz and evidence of higher modes above 0.8 Hz. A strong correlation between noise levels in the borehole and local sea state conditions is observed along with clear observation of the nonlinear frequency doubling effect between ocean surface waves and microseisms. Particle motion analysis further verifies that noise propagates through the array as Rayleigh/Stoneley waves. Polarization direction indicates at least two sources; distant westerly swell during quiescent times and local surface waves due to a passing storm. Above 1.0 Hz the LFASE data shows little coherence and displays random polarization. Because of this, we believe scattered energy is a significant component of the noise field in the Blake Bahama Basin. A fully 3-D finite difference algorithm is used to model both surface and volume heterogeneities in the ocean crust. Numerical modeling of wave propagation for hard and soft bottom environments shows that heterogeneities on the order of a seismic wavelength radiate energy into the water column and convert acoustic waves in the water into small wavelength Stoneley waves observed at the borehole. Sea floor roughness is the most important elastic scattering feature of the ocean crust. Comparisons of 2D and 3D rough sea floor models show that out-of-plane effects necessitate the use of 3D methods. The out-of-plane energy that is present in the LFASE data comes from either heterogeneities in the source field (i.e. mixed gravity wave directions) or, equally likely, scattering of the source field from surface or volume heterogeneities in the sea floor.
Author:
Publisher:
ISBN:
Category : Engineering
Languages : en
Pages : 966
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Author: Lawrence J. Fusillo
Publisher:
ISBN:
Category :
Languages : en
Pages : 216
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Author: BENJAMIN F. CRON
Publisher:
ISBN:
Category :
Languages : en
Pages : 1
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OBSERVATIONS INDICATE THAT NOISE IN THE OCEAN I A SUPERPOSITION OF AN ISOTROPIC NOISE FIELD AND AN ANISOTROPIC NOI E FIELD ORIGINATING AT THE SURFACE. Models which produce such noise fields are described, and the spatial correlation functions are ob ained. The volume noise model, which produces an isotropic noise field, consists of noise sources uniformly distributed within a sphere. A single frequency of each noise source is considered; the frequency and mean square output of each are the same, the relative phases are random, and inverse spreading occurs. For a very large sphere the spatial correlation is the same as that given by Marsh for a homogeneous isotropic noise field and by the Faran and Hills noi e model, which consists of noise sources on the surface of a large sphere. The surface noise model consists of noise sources uniformly distributed on a large circular area of a plane. The noise sources are assumed to be directional in addition to having the properties listed above. The spatial correlation i obtained as a function of the directionality of the noise sources, the spacing of the receivers and their orientation with respect to the surface, and the elec rical delay. Results for the two noise models are compared in relation to signal-to-noise gain of hydrophone arrays. (Author).
Author: Carina C. Juretzek
Publisher:
ISBN:
Category :
Languages : en
Pages :
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