How to Influence the Low Frequency Output of Marine Air-gun Arrays

2011 ◽  
Author(s):  
G. E. Parkes ◽  
S. Hegna
Keyword(s):  
Low Frequency ◽  
Air Gun ◽  
Frequency Output ◽  
Marine Air

Delaying the source ghost to improve the ultralow-frequency response of a marine air-gun source

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. P45-P51
Author(s):  
Honglei Shen ◽  
Thomas Elboth ◽  
Chunhui Tao ◽  
Gang Tian ◽  
Hanchuang Wang ◽  
...  
Keyword(s):  
Seismic Data ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Ultralow Frequency ◽  
Full Waveform ◽  
Air Gun ◽  
Marine Source ◽  
Frequency Output ◽  
Marine Seismic ◽  
Marine Air

The competing effect between the fundamental bubble and its source-ghost response results in a strong attenuation of the lowest frequencies (below 7 Hz). This loss cannot be compensated easily by adjusting the source depth. Consequently, the low-frequency content in marine seismic data is not optimal, degrading the performance of low-frequency dependent processing approaches, such as full-waveform inversion. To overcome this, we have developed an additional source to counteract the ghost from the main source. In this situation, the fundamental bubble is characterized by the depth of the main source, whereas the ghost response is characterized by the summed depth of the main and additional sources. This source setup mitigates the competing effect and reduces the suppression of ultralow frequencies. Compared with a conventional horizontal source, our source design will reduce the mid- to high-frequency output, which may be beneficial in situations in which environmental constraints limit the maximum allowed output of a marine source.

Estimation of bubble time period for air-gun clusters using potential isosurfaces

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. P1-P7 ◽  
Author(s):  
Daniel Barker ◽  
Martin Landrø
Keyword(s):  
Kinetic Energy ◽  
Incompressible Flow ◽  
Potential Field ◽  
Arbitrary Number ◽  
Low Frequency ◽  
Air Gun ◽  
Time Period ◽  
Frequency Output ◽  
Equilibrium Radius ◽  
Relative Change

We evaluated a method of estimating the relative bubble time period of air-gun clusters with an arbitrary number of guns. This was done by assuming incompressible flow and representing the bubbles as isosurfaces of the potential field to account for coalescence. The kinetic energy at the equilibrium radius was then compared to the equivalent energy of the single gun to estimate the relative change. The results agreed well with two-gun cluster measurements, but the lack of data does not allow us to compare with clusters containing more guns than that. We found that more compact configurations, such as a triangle instead of three guns in a line, gave a more rapid increase in the bubble time period as the gun separation decreased. This indicated that compact configurations were attractive for enhancing the low-frequency output from an air-gun cluster.

scholarly journals A long-offset seismic reflection and refraction study of the Gippsland and Bass Basins from onshore recording of a marine air-gun source

1989 ◽  
Vol 20 (2) ◽  
pp. 293
Author(s):  
C.D.N. Collins ◽  
J.P. Cull ◽  
J.B. Willcox ◽  
J.B. Colwell
Keyword(s):  
Deep Structure ◽  
Seismic Refraction ◽  
Reflection And Refraction ◽  
Air Gun ◽  
Long Offset ◽  
Deep Crustal Structure ◽  
Basin Formation ◽  
Seismic Refraction Data ◽  
Marine Air ◽  
Refraction Data

Seismic refraction data were obtained for the Bass and Gippsland Basins during the 1988 cruise of the BMR research vessell "Rig Seismic". Seismic recorders were deployed on land by BMR and Monash University to record long-offset wide-angle reflection and refraction data using the ship's air-guns as the energy source. Preliminary results have now been obtained from these data providing information on deep crustal structure related to the basin formation. Two crustal layers have been detected with velocities of 4.5 km/s increasing to 7.4 km/s (unreversed) at depths exceeding 20 km. Additional data have now been obtained over a traverse length of 170 km to provide constraints on the deep structure of Bass Strait and the Lachlan Fold Belt in Victoria and Tasmania.

On the theory of air‐gun bubble interactions

Geophysics ◽  
1988 ◽  
Vol 53 (2) ◽  
pp. 192-200 ◽  
Author(s):  
R. C. Bailey ◽  
P. B. Garces
Keyword(s):  
Ambient Pressure ◽  
Bubble Radius ◽  
Dynamical Equations ◽  
Local Pressure ◽  
Know How ◽  
R And D ◽  
Bubble Interactions ◽  
Interaction Terms ◽  
Air Gun ◽  
Marine Air

Calculation of the seismic signatures of marine air‐gun arrays often requires that the interactions among the bubbles from air guns be taken into account. The standard method of doing this is to use the Giles‐Johnston approximation in which a time‐dependent effective ambient pressure is calculated for each bubble as the sum of the true ambient pressure and the local pressure signals of all the other bubbles in the array. These effects of interaction have a relative importance in the dynamics proportional to (R/D), where R and D are the typical bubble radius and interbubble separation, respectively. To ensure that current methods of calculating signatures are accurate, it is necessary to know how good this approximation is. This paper shows that there are no interaction terms in the full dynamical equations proportional to [Formula: see text] or [Formula: see text], and that the errors of the Giles‐Johnston approximation are only of order [Formula: see text]. The Giles‐Johnston approximation is therefore justified even for fairly accurate signature calculations for noncoalescing bubbles. The analysis here also shows how to incorporate bubble motions and deformations into the dynamical equations, so that the errors can be reduced to order [Formula: see text] if desired.

scholarly journals Streamer depth versus vessel and seismic interference noise

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. P41-P51
Author(s):  
Toan Dao ◽  
Martin Landrø
Keyword(s):  
Noise Level ◽  
Cutoff Frequency ◽  
Normal Modes ◽  
Low Frequency ◽  
Data Set ◽  
The North ◽  
Interference Noise ◽  
Air Gun ◽  
Seismic Surveying ◽  
Marine Seismic

For marine seismic surveying, it is commonly assumed that the noise level decreases with depth. In addition, recent advances in broadband seismic have shown that a greater receiver depth is beneficial in preserving low-frequency data. However, in a heavily trafficked ocean, noise from other ships, including seismic interference, is a counteractive process in which the noise actually varies with depth. Normal modes can be used to explain and predict the ship noise and seismic interference noise level. We find that weather noise is dominant below the first mode’s cutoff frequency (approximately 6 Hz), ship noise is dominant from that frequency to the upper end of the useful seismic frequency band (80 Hz). We have used a data set in which the streamer was towed at 8, 45, and 60 m depths in three passes over the same area in the North Sea. The water depth is 135 m on average. We observe that the noise level at 45 and 60 m depth is approximately 1.6 times stronger than that at 8 m. We find that the air-gun energy is up to 46 dB stronger than the noise from the seismic vessel. However, the total noise from all the ships within several hundred kilometers radius can reduce the data quality.

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