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- Volume 6, Issue 9, 1988
First Break - Volume 6, Issue 9, 1988
Volume 6, Issue 9, 1988
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A changing philosophy in seismic data acquisition
More LessThe primary task of seismic data acquisition is to produce a data set from which the recorded wavefield can be reconstructed at any time and at any place with maximum fidelity. This should be followed in the processing phase by the full inversion of the wavefield in order to reconstruct our exploration targets. The technical requirement for such acquisition is a spatially wide-band recording system with minimum distortion. As far as possible, the desired and undesired events should remain separable, and the ability to correct for imperfections should be retained. Traditionally, one task of seismic data acquisition has been to immediately commence improvements of the apparent signal-to-noise ratio in the field. The main tools for this have been the use of geometrical shot and receiver arrays to suppress dominant noise arrivals. Unfortunately this has usually been done by comparing field records acquired with different experimental parameters, but without the primary physical objectives kept in mind. Neither spatial distortion, whether linear or non-linear nor the spatial or temporal separability of wanted and unwanted events, can be assessed by looking at raw field records. The physics of the discrete recording, anti-alias filtering and re-sampling, with the objective of maintaining the information within a defined bandwidth, is well known, in particular for time series. There is no reason why spatial samples should not be handled in the same way as temporal samples. Therefore, one could record spatially with an essentially similar approach to that used for the time domain, and provide selectivity later in the subsequent processing phase. This would simplify the data acquisition to a general measuring system and would provide endless processing possibilities without initial acquisition commitment. In addition a high degree of standardization would be obtained. Such a system for 'hands-off' acquisition was described by Ongkiehong and Askin (1988) and has already been implemented in worldwide operations. Additional hardware developments could make this method and any other seismic system even more powerful.
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The marine vibrator source
Authors G. Baeten, J. Fokkema and A. ZiolkowskiAfter the introduction of thc Vibroseis principle in seismic exploration in the early 1960s, considerable effort has been put in the development of a marine version of the land vibrator. Figure 1 shows one of the latest versions of the marine vibrator. The incentive for the development of thc marine vibrator was the feeling that further refinement of available marine sources was insufficient tor future explorarion needs. The marine vibrator's ability to fill this gap lies mainly in the perfect control that one has, at least in principle, over the emitted source signal. Further the marine vibrator can be used in shallow water areas, where conventional seismic sources are difficult to deploy. Our aim is to investigate some gcophysical issues related to the performance of the marine vibrator. For this purpose, we start with a description of the Vibroseis principle. Since the Vibroseis method has been and is being used extensively on land, problems and important aspects of the marine vibrator performance can he deduced from more than 20 years of experience with land vibrators. Also, differences in performance between land and marine vibrators will be discussed. A particular issue that deserves attention is the choice of the signal that should be monitored on the vibrator for phase and amplitude control. This choice is intimately related to the way the wavefield behaves in the far field. Also, the power output of the vibrator is of great practical importance and is investigated here. To analyse these problems we develop a model of the marine vibrator and its surrounding medium. The model contains three elements: (1) a description of the propagation of seismic waves in the medium, (2) a formulation of the boundary conditions at the surface of the vibrator, and (3) a description of the mechanical properties of the vibrator. Finally, some real data examples are shown, and a comparison is made between the model results and the measurements.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)