AIR-GUN BUBBLE DAMPING BY A SCREEN

A method for damping unwanted bubble oscillations from a seismic air g un is presented. The method exploits the fact that the primary pressur e peak generated by an air gun is produced during the first 5-10 ms af ter firing. The air bubble is destroyed by mounting a perforated scree n with an optimal radius about the gun. Once the primary pressure peak has been generated by the bubble, the bubble is destroyed by the scre en, leading to a corresponding decrease in the measured pressure ampli tude of the secondary bubble oscillations. Controlled near-field measu rements of 40-cubic inch and 120-cubic inch air guns with and without damping screens are used. The primary to bubble ratio improves from 1. 4 without a screen to 4.4 with a screen in the near-field. The corresp onding values for estimated far-field signatures are 1.8 to 9.0 when t he signatures are filtered with an out-128 Hz (72 dB/Oct) DFS V filter .