Damping of secondary bubble oscillations for towed air guns with a screen

Abstract A method for damping unwanted bubble oscillations from a horizontally towed seismic air gun is presented. The air bubble is destroyed by a perforated screen mounted at an optimal radius about the gun. Once the primary pressure peak has been generated by the emerging bubble, the bubble continues to expand and is destroyed by the screen, leading to a corresponding decrease in the measured pressure amplitude of the secondary bubble oscillations. For a stationary gun fired first without, and then with, the screen fitted, the primary-to-bubble ratio improves in the near field from 1.7 to 5.2, respectively, at a firing depth of 3 m and from 1.5 to 5.5, respectively, at 5 m depth. The primary-to-bubble ratio for a towed air gun in the quasi-far-field improves from 2.0 to 11.0 at 4 m depth and from 1.5 to 8.7 at 7 m depth when the screen is fitted. The boat speed was 1.6 knots and the signatures were filtered with an out-128 Hz (72 dB/Oct) DFS V filter.