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

Abstract

We have refined our system for calculating the signa; ture 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.

Vertical movements and material transport during hotspot activity: Seismic reflection profiling offshore La Réunion

“…Theoretically, the far-field source signature can be estimated from near-field measurements [Ziolkowski et al, 1982;Parkes et al, 1984]. Each gun was equipped with a near-field hydrophone, but most of them ceased to work as soon as the guns were put in the water, which meant that it would be impossible to follow the procedure described by Ziolkowski [1987].…”

Tools and Techniques: Marine Seismic Methods

“…In such cases, clustered air guns are typically used (Dragoset, 1990). Ziolkowski et al (1982) and Parkes et al (1984) showed how the monopole source function (termed the 'notional source signature' by them) could be measured using a hydrophone placed about 1 m from the air gun bubble. The VSP source obtains its spectral flatness by using clusters rather than by using a large mix of volumes.…”

“…Landr and Sollie (1992) constrained them to be solutions of the bubble equation of motion (described in the succeeding text); Amundsen (1993a) allowed them to be arbitrary functions. These two methods and that of Ziolkowski et al (1982) combined with Parkes et al (1984) were compared by Laws et al (1998) to measurements made with a farfield hydrophone, and the three methods were found to be of similar accuracy. Ziolkowski (1980) had proposed a method using 'scaled arrays,' but this involved doubling the shot interval and was not adopted.…”

ENERGY‐INTERACTION: THE LONG‐RANGE INTERACTION OF SEISMIC SOURCES1

“…For each experiment, the near-field measurements were used to compute the notional signatures after the method described by Parkes, Ziolkowski, Hatton and Haugland (1984). From the notional signatures thus obtained, the field may be computed at any point in space; in particular, the far-field values are easily determined.…”