Method for seismic marine survey

A method of marine seismic prospecting comprising the steps of:

• establishing a bubble containing a high-pressure expanding volume of gas at a sufficient depth to prevent the gas from directly venting to the atmosphere;
• the initial expansion of said gas bubble generating in the water a desired initial acoustic impulse for subsequent reflection from the sub-bottom strata;
• said gas bubble subsequent to said initial expansion collapsing and again expanding to create in the water at least a first bubble acoustic impulse which also becomes reflected from said sub-bottom strata;
• detecting the reflected signals from said initial impulse and said first impulse;
• and
• detecting the unreflected acoustic impulses with at least one pressure detector assembly, said detector assembly comprising:
• (a) a housing having a flexible, pressure-transmitting wall defining a chamber;
• (b) a substantially incompressible dielectric liquid completely filling said chamber,
• (c) a detector probe completely immersed in said liquid, said probe comprising:
• a metallic housing, a quartz crystal mounted on an inner wall portion of said housing, an amplifier in said housing, and circuit means coupling said quartz crystal to the input circuit of said amplifier;
• and
• recording at a remote location the output signals from said amplifier, said output signals representing said unreflected acoustic impulses.