Page 76 - Acquisition and Processing of Marine Seismic Data

2.2 AIR GUN ARRAYS 67

FIG. 2.24 (A) Typical near-field signature of a single air gun. (B) Amplitude spectrum of the far-field signature of an air gun
signal fired at 6 m depth.

fired with a small time interval via two dedicated which produces the air bubble and the primary
discharge ports (Fig. 2.25). A GI gun basically seismic signal (Fig. 2.25A). Then the bubble starts
worksastwoindependentconventionalairguns. to expand and, whenever it reaches its maximum
When a shot point is reached, the generator size, the injector chamber is fired directly into
chamber is fired first at the air gun aim point, the existing air bubble just before it starts to

FIG. 2.25 Schematic illustration of the working principle of a GI gun. (A) Generator chamber is fired first to generate the air
bubble and seismic signal. (B) During the expansion of bubble, the injector chamber is fired directly into the air bubble when it
reaches its maximum size. (C) Firing of the injector increases the internal pressure of the bubble and prevents shrinking.