A COMPARISON BETWEEN SONOBUOY AND OCEAN BOTTOM SEISMOGRAPH DATA AND CRUSTAL STRUCTURE OF THE TEXAS SHELF ZONE

Geophysics ◽  
1978 ◽  
Vol 43 (3) ◽  
pp. 514-527 ◽  
Author(s):  
Abou‐Bakr K. Ibrahim ◽  
Gary V. Latham
Keyword(s):  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Vertical Component ◽  
Shelf Zone ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Distance Curve ◽  
Resonant Frequencies ◽  
Ocean Bottom Seismograph ◽  
Better Than

Three refraction profiles were shot in the Gulf of Mexico 100 nautical miles south of Galveston. Recordings were made using free floating and anchored sonobuoys deployed near an ocean bottom seismograph (OBS). Explosions and airgun sources were used. Vertical component geophones with resonant frequencies of 4.5 Hz and 8 Hz were used in the OBS system. We compared seismic data recorded by the conventional sonobuoy and the OBS. The signal‐to‐noise ratio for the OBS is about three to four times better than that of the sonobuoy, facilitating the interpretation of the three profiles. Based on the first and later arrivals obtained from the OBS records, traveltime curves and an amplitude distance curve are constructed. The results show that the velocities at the experimental sites vary between 1.7 km/sec at the surface to 7.7 km/sec at a depth of 14.5 km. The 7.7 km/sec layer may be lower crust or anomalous mantle. The low velocity sediments (1.7 – 3.3 km/sec) thicken westward from the deployment point.

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.

scholarly journals Infrared Stripe Correction Algorithm Based on Wavelet Analysis and Gradient Equalization

2019 ◽  
Vol 9 (10) ◽  
pp. 1993 ◽  
Author(s):  
Ende Wang ◽  
Ping Jiang ◽  
Xukui Hou ◽  
Yalong Zhu ◽  
Liangyu Peng
Keyword(s):  
Wavelet Analysis ◽  
Infrared Imaging ◽  
Signal To Noise Ratio ◽  
Vertical Component ◽  
Infrared Image ◽  
Structural Similarity ◽  
Correction Algorithm ◽  
Uncooled Infrared Imaging ◽  
Correction Result ◽  
Better Than

In the uncooled infrared imaging systems, owing to the non-uniformity of the amplifier in the readout circuit, the infrared image has obvious stripe noise, which greatly affects its quality. In this study, the generation mechanism of stripe noise is analyzed, and a new stripe correction algorithm based on wavelet analysis and gradient equalization is proposed, according to the single-direction distribution of the fixed image noise of infrared focal plane array. The raw infrared image is transformed by a wavelet transform, and the cumulative histogram of the vertical component is convolved by a Gaussian operator with a one-dimensional matrix, in order to achieve gradient equalization in the horizontal direction. In addition, the stripe noise is further separated from the edge texture by a guided filter. The algorithm is verified by simulating noised image and real infrared image, and the comparison experiment and qualitative and quantitative analysis with the current advanced algorithm show that the correction result of the algorithm in this paper is not only mild in visual effect, but also that the structural similarity (SSIM) and peak signal-to-noise ratio (PSNR) indexes can get the best result. It is shown that this algorithm can effectively remove stripe noise without losing details, and the correction performance of this method is better than the most advanced method.

scholarly journals Integrated magnetotelluric and seismic investigation of Cenozoic graben structure near Obrzycko, Poland

2021 ◽  
Author(s):  
Adam Cygal ◽  
Michał Stefaniuk ◽  
Anna Kret
Keyword(s):  
Seismic Data ◽  
Geophysical Methods ◽  
Geological Structure ◽  
Data Sets ◽  
Low Velocity ◽  
Shallow Subsurface ◽  
Geophysical Model ◽  
Novel Approach ◽  
Loose Deposits ◽  
Static Corrections

AbstractThis article presents the results of an integrated interpretation of measurements made using Audio-Magnetotellurics and Seismic Reflection geophysical methods. The obtained results were used to build an integrated geophysical model of shallow subsurface cover consisting of Cenozoic deposits, which then formed the basis for a detailed lithological and tectonic interpretation of deeper Mesozoic sediments. Such shallow covers, consisting mainly of glacial Pleistocene deposits, are typical for central and northern Poland. This investigation concentrated on delineating the accurate geometry of Obrzycko Cenozoic graben structure filled with loose deposits, as it was of great importance to the acquisition, processing and interpretation of seismic data that was to reveal the tectonic structure of the Cretaceous and Jurassic sediments which underly the study area. Previously, some problems with estimation of seismic static corrections over similar grabens filled with more recent, low-velocity deposits were encountered. Therefore, a novel approach to estimating the exact thickness of such shallow cover consisting of low-velocity deposits was applied in the presented investigation. The study shows that some alternative geophysical data sets (such as magnetotellurics) can be used to significantly improve the imaging of geological structure in areas where seismic data are very distorted or too noisy to be used alone

scholarly journals No mafic layer in 80 km thick Tibetan crust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gaochun Wang ◽  
Hans Thybo ◽  
Irina M. Artemieva
Keyword(s):  
Seismic Data ◽  
P Wave ◽  
Indian Plate ◽  
Low Velocity ◽  
Crustal Earthquakes ◽  
Tectonic Processes ◽  
P Wave Velocity ◽  
Juvenile Crust ◽  
Mafic Lower Crust ◽  
Thick Crust

AbstractAll models of the magmatic and plate tectonic processes that create continental crust predict the presence of a mafic lower crust. Earlier proposed crustal doubling in Tibet and the Himalayas by underthrusting of the Indian plate requires the presence of a mafic layer with high seismic P-wave velocity (Vp > 7.0 km/s) above the Moho. Our new seismic data demonstrates that some of the thickest crust on Earth in the middle Lhasa Terrane has exceptionally low velocity (Vp < 6.7 km/s) throughout the whole 80 km thick crust. Observed deep crustal earthquakes throughout the crustal column and thick lithosphere from seismic tomography imply low temperature crust. Therefore, the whole crust must consist of felsic rocks as any mafic layer would have high velocity unless the temperature of the crust were high. Our results form basis for alternative models for the formation of extremely thick juvenile crust with predominantly felsic composition in continental collision zones.

scholarly journals Velody 2—Resilient High-Capacity MIDI Steganography for Organ and Harpsichord Music

2020 ◽  
Vol 11 (1) ◽  
pp. 39
Author(s):  
Eric Järpe ◽  
Mattias Weckstén
Keyword(s):  
Mean Absolute Error ◽  
Signal To Noise Ratio ◽  
High Capacity ◽  
Absolute Error ◽  
Music Technology ◽  
Alternative Methods ◽  
File Size ◽  
User Friendly ◽  
Different Levels ◽  
Better Than

A new method for musical steganography for the MIDI format is presented. The MIDI standard is a user-friendly music technology protocol that is frequently deployed by composers of different levels of ambition. There is to the author’s knowledge no fully implemented and rigorously specified, publicly available method for MIDI steganography. The goal of this study, however, is to investigate how a novel MIDI steganography algorithm can be implemented by manipulation of the velocity attribute subject to restrictions of capacity and security. Many of today’s MIDI steganography methods—less rigorously described in the literature—fail to be resilient to steganalysis. Traces (such as artefacts in the MIDI code which would not occur by the mere generation of MIDI music: MIDI file size inflation, radical changes in mean absolute error or peak signal-to-noise ratio of certain kinds of MIDI events or even audible effects in the stego MIDI file) that could catch the eye of a scrutinizing steganalyst are side-effects of many current methods described in the literature. This steganalysis resilience is an imperative property of the steganography method. However, by restricting the carrier MIDI files to classical organ and harpsichord pieces, the problem of velocities following the mood of the music can be avoided. The proposed method, called Velody 2, is found to be on par with or better than the cutting edge alternative methods regarding capacity and inflation while still possessing a better resilience against steganalysis. An audibility test was conducted to check that there are no signs of audible traces in the stego MIDI files.

Sub-Moho seismic profile in the Mariana Basin — Ocean bottom seismograph long-range explosion experiment

1981 ◽  
Vol 53 (1) ◽  
pp. 93-102 ◽  
Author(s):  
S. Nagumo ◽  
T. Ouchi ◽  
J. Kasahara ◽  
S. Koresawa ◽  
Y. Tomoda ◽  
...  
Keyword(s):  
Long Range ◽  
Seismic Profile ◽  
Ocean Bottom ◽  
Ocean Bottom Seismograph ◽  
Explosion Experiment

Downward and upward continuation of 2-D seismic data to eliminate ocean bottom topography’s effect

2010 ◽  
Vol 7 (2) ◽  
pp. 149-157 ◽  
Author(s):  
Xiang-Chun Wang ◽  
Chang-Liang Xia ◽  
Xue-Wei Liu
Keyword(s):  
Seismic Data ◽  
Ocean Bottom ◽  
Upward Continuation
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