ACTIVE SIGNAL GENERATOR FOR MARINA ONDAMAL

摘要

A source is described capable of generating acoustic signals under water at high cycling rates suitable for providing seismic signals of controlled amplitude and spectral shape and with precise timing for geophysical exploration. The source has a pair of radiating pistons in a housing having a cylindrical sleeve and radial webs. Axial shafts extend outwardly from the pistons and support the pistons in the webs. The peripheral edges of the pistons are in sliding contact with and are guided by the sleeve. The pistons and sleeve define a chamber between the pistons which, under quiescent conditions, contains gas under a low pressure or partial vacuum. The shaft on at least one of the pistons extends into another chamber in the hub of one of the webs. Pressurized hydraulic fluid is caused to flow into this chamber via a valve mechanism to cause the pistons to execute cycles in which they move toward each other to an impact position, due to the ambient pressure of the surrounding water, and then rebound away from each other by virtue of a mass-spring system which is defined by the pistons and may also include the compressed gas in the chamber between the pistons which cushions the impact and shapes the acoustic signal. A control system, which may be responsive to the acoustic signal in the water, detects when the pistons reach impact position, and provides for the timing and duration of the cycle to be precisely controlled, with acoustic signals of desired amplitude being produced precisely at the desired times and with the pistons being reset in their outward position ready for the next cycle in a minimum time and without unwanted acoustic transients such that the acoustic signals can be generated at high cycling rates. The source is suitable for use in arrays where any individual source provides transmitted signals which are timed to occur simultaneously or sequentially in relation to the signals provided by the other sources.