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FIG. R-5. Rayleigh-Willis relation for representative energy sources. Source depth=9 m. (Courtesy Bendix United Geophysical.)

An oscillating bubble of gases, such as formed by an explosion in water. Most marine seismic sources generate bubbles; the bubble oscillation frequency is given by the Rayleigh-Willis relation (see Figure R-5). Various arrangements such as wave-shape kits are used to attenuate bubble effects or (as with Maxipulse) to correct for them. Bubble oscillations can be prevented if the source is so close to the surface that the gases vent before the bubble collapses. This occurs if an explosive of w pounds of dynamite is fired shallower than d ft, where d=3.8w1/3. See Figure B-10.

FIG. B-10. Bubble pulses from a small underwater explosion. The time between successive implosions decreases as energy is dissipated. Successive pulses effectively generate additional records superimposed on the first; the result is bubble noise. One measure of the effectiveness of a marine source is the ratio of the amplitudes of the primary to the first bubble. See also Figure S-16. (Courtesy Chevron Oil Co.)

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