Seismic investigation of underwater geological formations - using bubble-noise-suppressing, air-cannon acoustic source at shallow depths

摘要

Acoustic signals for seismic exploration are generated by allowing compressed gas to escape at a predetermined depth in a volume of water. The first emitted sections of the acoustic signals are amplified and the later emitted sections are damped by echo signals derived from the generated signals and reflected from the surface of the water, whilst the acoustic signals derived from the generated signals and propagated through the ground formations beneath the water are detected. Specifically, during generation, acoustic signals are originated at a predetermined depth. This has the result that twice the acoustic transmission time from the depth to the surface of the water, is about equal to the duration of the first half cycle of the first emitted section of each signal generated. The signals are generated at a depth of pref. 1.50-4.50 m, esp. 3m beneath the surface of the water. Method overcomes problems of bubble oscillation, and provides a means of transmitting considerably improved signals from an underwater acoustic source.