DAMPING OF SECONDARY BUBBLE OSCILLATIONS FOR TOWED AIR-GUNS WITH A SCREEN

A method for damping unwanted bubble oscillations from a horizontally towed seismic air gun is presented. The air bubble is destroyed by a p erforated screen mounted at an optimal radius about the gun. Once the primary pressure peak has been generated by the emerging bubble, the b ubble continues to expand and is destroyed by the screen, leading to a corresponding decrease in the measured pressure amplitude of the seco ndary bubble oscillations. For a stationary gun fired first without, a nd then with, the screen fitted, the primary-to-bubble ratio improves in the near held 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-bub ble 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 filte red with an out-128 Hz (72 dB/Oct) DFS V filter.