The signature of an air gun array: Computation from near‐field measurements including interactions—practical considerations

1982 ◽  
Author(s):  
G. E. Parkes ◽  
A. Ziolkowski ◽  
L. Hatton ◽  
T. Haugland
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Air Gun

Single water gun far‐field pressure signatures estimated from near‐field measurements

Geophysics ◽  
1985 ◽  
Vol 50 (2) ◽  
pp. 257-261 ◽  
Author(s):  
M. H. Safar
Keyword(s):  
High Resolution ◽  
Data Acquisition ◽  
Seismic Data ◽  
Near Field ◽  
Field Measurements ◽  
Reference Source ◽  
Far Field ◽  
Air Gun ◽  
Seismic Data Acquisition ◽  
Marine Seismic

An important recent development in marine seismic data acquisition is the introduction of the Gemini technique (Newman, 1983, Haskey et al., 1983). The technique involves the use of a single Sodera water gun as a reference source together with the conventional air gun or water gun array which is fired a second or two after firing the reference source. The near‐field pressure signature radiated by the reference source is monitored continuously. The main advantage of the Gemini technique is that a shallow high;resolution section is recorded simultaneously with that obtained from the main array.

On: “The signature of an air gun array: Computation from near field measurements including interactions” by A. Ziolkowski, G. Parkes, L. Hatton, and T. Haugland (GEOPHYSICS, v. 47, p. 1413–1421, October, 1982).

Geophysics ◽  
1984 ◽  
Vol 49 (11) ◽  
pp. 2067-2068
Author(s):  
M. H. Safar
Keyword(s):  
Hydrostatic Pressure ◽  
Dynamic Pressure ◽  
Near Field ◽  
Field Measurements ◽  
Air Bubbles ◽  
Surrounding Water ◽  
Radiation Impedance ◽  
Air Bubble ◽  
Air Gun ◽  
Third Law

I would like to make two comments regarding the discussion on interaction between air bubbles given by Ziolkowski et al. The first concerns their statement that their approach for treating interaction is exactly the same as my approach (Safar, 1976), namely, that interaction is treated as a modulation of the hydrostatic pressure just outside the air bubbles. I would like to emphasize that, in fact, this was the approach used by Giles and Johnston (1973) and not the approach that I used in my paper. Since the problem of interaction between seismic sources forming an array is of considerable importance from the operational viewpoint, I give a summary of the analysis which I gave in my paper. Consider the case of two identical air guns placed at the same depth. When only one gun is fired, one air bubble is produced. From Newton’s third law, the effective pressure acting on the pulsating air bubble is not equal to the hydrostatic pressure as was stated by Ziolkowski et al., but equal to the hydrostatic pressure [Formula: see text] plus the dynamic pressure exerted by the surrounding water which is given by [Formula: see text], (1) where the dot denotes differentiation with respect to time t, v(t) and [Formula: see text] are the air bubble instantaneous volume and radiation impedance.

On: “The signature of an air gun array: Computation from near‐field measurements including interactions”, by A. Ziolkowski, G. Parkes, L. Hatton, and T. Haugland (GEOPHYSICS, 47, p. 1413–1421.)

Geophysics ◽  
1983 ◽  
Vol 48 (9) ◽  
pp. 1293-1293
Author(s):  
Erhard Wielandt
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Air Gun ◽  
Pressure Term ◽  
Flow Pressure ◽  
Bubble Oscillations

I wish to put forward a few arguments in favor of the after‐flow pressure term which Keller and Kolodner (1956) retain in their calculation of bubble oscillations and which Ziolkowski et al consider as “absolutely negligible.”

The signature of an air gun array: Computation from near‐field measurements including interactions—Practical considerations

Geophysics ◽  
1984 ◽  
Vol 49 (2) ◽  
pp. 105-111 ◽  
Author(s):  
G. E. Parkes ◽  
A. Ziolkowski ◽  
L. Hatton ◽  
T. Haugland
Keyword(s):  
Pressure Field ◽  
Near Field ◽  
Field Measurements ◽  
Weather Conditions ◽  
Normal Operation ◽  
Far Field ◽  
Iterative Technique ◽  
Forward Motion ◽  
Air Gun ◽  
Bad Weather

We have refined our system for calculating the signature of an interacting air gun array from near‐field measurements of its pressure field. We use an iterative technique to calculate a notional array of noninteracting sources from the near‐field hydrophone measurements. The notional signatures form the basis for calculating the array signature in any direction. The success of our iterative technique depends upon prudent positioning of the hydrophones, one close to each air gun. In normal operation the forward motion of the hydrophones and upward motion of the air gun bubbles are important effects which must be included in the equations. A linear model for this motion is adequate and improves the method significantly. The vertically traveling “far‐field” signature calculated by our extended method matches an equivalent “far‐field” measurement very closely. We present array signatures obtained in very bad weather conditions (force 8). In this extreme test the signatures are very stable from shot to shot. Therefore it is not necessary to calculate the array signature every shot; however, continuous recording of near‐fields should still be carried out as a check on signature stability.

Air‐gun bubble damping by a screen

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1765-1772 ◽  
Author(s):  
Jan Langhammer ◽  
Martin Landrø ◽  
James Martin ◽  
Eivind Berg
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Far Field ◽  
Pressure Amplitude ◽  
Air Bubble ◽  
Air Gun ◽  
Pressure Peak ◽  
Bubble Oscillations ◽  
Measured Pressure ◽  
Optimal Radius

A method for damping unwanted bubble oscillations from a seismic air gun is presented. The method exploits the fact that the primary pressure peak generated by an air gun is produced during the first 5–10 ms after firing. The air bubble is destroyed by mounting a perforated screen with an optimal radius about the gun. Once the primary pressure peak has been generated by the bubble, the bubble is destroyed by the screen, leading to a corresponding decrease in the measured pressure amplitude of the secondary bubble oscillations. Controlled near‐field measurements of 40‐cubic inch and 120‐cubic inch air guns with and without damping screens are used. The primary to bubble ratio improves from 1.4 without a screen to 4.4 with a screen in the near‐field. The corresponding values for estimated far‐field signatures are 1.8 to 9.0 when the signatures are filtered with an out‐128 Hz (72 dB/Oct) DFS V filter.

Estimation of source signatures from air guns fired at various depths: A field test of the source scaling law

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. P13-P22 ◽  
Author(s):  
Kjetil E. Haavik ◽  
Martin Landrø
Keyword(s):  
Correction Term ◽  
Near Field ◽  
Scaling Law ◽  
Field Measurements ◽  
Air Gun ◽  
Time Period ◽  
Source Scaling ◽  
Seismic Data Acquisition ◽  
The Difference ◽  
The Given

Recent advances in marine broadband seismic data acquisition have led to a range of new air-gun source configurations. The air-gun arrays have conventionally been kept at a constant depth, but to attenuate the source-side ghost reflection, new source strategies involving multiple source depths have been proposed. The bubble-time period for an air-gun bubble is dependent on, among many parameters, the firing depth. We use quasi near-field measurements of air-gun signatures to validate a version of the well-known source scaling law in which the characteristic bubble-time period is used as the scale. We find that the source scaling law can be used to estimate a source signature from one depth knowing the source signature at a different depth from the same gun. Furthermore, we derive a correction term to the Rayleigh-Willis bubble-time equation to correct for the fact that interaction between the bubble and free surface reduces the bubble-time period. This correction term improves our results significantly for air guns positioned close to the air-water interface. The error between the estimated and measured source signatures is dependent on the difference in source depth. For a depth difference of [Formula: see text], we estimate signatures that have NRMS differences ranging between 5% and 6% from the measured signature at the given depth and between 8% and 12% when the difference is [Formula: see text].

The signature of an air gun array: Computation from near‐field measurements including interactions

Geophysics ◽  
1982 ◽  
Vol 47 (10) ◽  
pp. 1413-1421 ◽  
Author(s):  
A. Ziolkowski ◽  
G. Parkes ◽  
L. Hatton ◽  
T. Haugland
Keyword(s):  
Seismic Waves ◽  
Pressure Field ◽  
Near Field ◽  
Patent Application ◽  
Field Measurements ◽  
Linear Superposition ◽  
Underlying Assumption ◽  
Spherical Waves ◽  
Air Gun ◽  
Made In

We designed a system to enable the signature of an air gun array to be calculated at any point in the water from a number of simultaneous independent measurements of the near‐field pressure field [subject of a patent application]. The number of these measurements must not be less than the number of guns in the array. The underlying assumption in our method is that the oscillating bubble produced by an air gun is small compared with the wavelengths of seismic interest. Each bubble thus behaves as a point source, both in the generation of seismic waves and in its response to incident seismic radiation produced by other nearby bubbles. It follows that the interaction effects between the bubbles may be described in terms of spherical waves. The array of interacting guns is equivalent to a notional array of noninteracting guns whose combined seismic radiation is identical. The seismic signatures of the equivalent independent elements of this notional array can be determined from the near‐field measurements. The seismic radiation pattern emitted by the whole array can be computed from these signatures by linear superposition, with a spherical correction applied. The method is tested by comparing far‐field signatures computed in this way with field measurements made in deep water. The computed and measured signatures match each other very closely. By comparison, signatures computed neglecting this interaction are a poor match to the measurements.

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