Abstract: The present invention relates to a system and a method for substantially eliminating flow noise from the signal output of each hydrophone in a hull mounted acoustic array. The system comprises a plurality of hydrophones forming an acoustic array mounted to a hull of a marine vessel, at least one reference hydrophone mounted to the hull in a laminar region of fluid flow over the hull, and a computational device for generating an output signal for each hydrophone in the acoustic array which is substantially free of flow noise using signals inputted from the acoustic array hydrophones and the at least one reference hydrophone.

Abstract: A simple mechanical device is provided which generates acoustic signals at ne or more specified depths. The device consists of a spring loaded piston placed in a wall of a housing, the spring loading biasing the piston away from the housing. The piston is subjected to a pressure differential between the exterior and interior of the housing such that the piston moves against the spring force and into the housing as the pressure differential, corresponding to a depth of the housing beneath a water surface, increases. As the piston moves further into the housing, it contacts a series of latches, each latch being used to detain spring loaded striker. The latches are spaced along the travel path of the piston such that each striker is associated with a specific piston movement, or depth. When the piston contacts a latch, the striker is released and strikes against a ledge within the housing, creating one of the acoustic signals.

Abstract: A simple, mechanical device is provided which produces an acoustic signal a specified depth. The device consists of a shear plug in an exterior wall of the device housing which prevents the movement of a spring biased piston. The plug is subjected to increasing differential pressure between the exterior and interior of the housing as the depth of the device beneath the water surface increases. At a known pressure differential, corresponding to a specified depth, the shear plug fails, allowing for the actuation of the piston. The spring biased piston strikes against a ledge in the device, creating the acoustic signal.

Abstract: A fiber optic bundle towed line array having a central strength member and plurality of longitudinal optical fibers spaced around the bundle near the array outer circumference. Each fiber has at least one in-line intensity modulated optical fiber hydrophone inserted at different preselected locations therealong. Patting material is molded around and embeds the optical fibers and the strength member so as to form a small diameter integral array unit.

Abstract: A sonobuoy for forming a plurality of virtual vertical arrays, the sonobuoy aving means for receiving and expelling water to cause said sonobuoy automatically to descend and rise in a water environment, whereby to form sequentially a plurality of virtual vertical arrays.

Abstract: The apparatus and method for determining the direction of an incoming sonar ignal using a towed array having at least two auxiliary transducers positioned along the array. Each auxiliary transducer contains a plurality of small transducers. By summing the output from each of the small transducers, thereby forming the outputs of the auxiliary transducers, and combining the output of the auxiliary transducers with the output of the towed array, the direction of arrival of a sonar signal impinging upon the towed array is determined.

Abstract: A water-activated sonobuoy system is provided to release a plurality of sle, water-activated sound sources into a water environment. In the preferred embodiment, a plurality of water-impenetrable tubes are attached and sealed at one end to a float and are open on their other end. A plurality of water-activated sound sources are stored within each tube. Water-degradable barriers are used to isolate each of the sound sources within the tubes. Water-degradable endcaps are used to seal the open end of each tube. Upon being placed in the water, the endcaps dissolve to release the first sound source in each tube. This in turn exposes the first barrier in the tube to water. Each exposed barrier subsequently dissolves in the water to release the next water-activated sound source in each tube. This process continues until all sound sources have been released into the water. Appropriate venting is provided in both the barriers and the float to permit controlled water entry from the bottom of the tubes.

Abstract: A means for extending the useful aperture of a multi-hydrophone towed array by using the overlap of the successive positions of the array hydrophones as the array moves forward through the water. The overlap information is used by an overlap correlator to provide phase correction factors for a synthetic aperture signal processing scheme. The overlap correlator continues to refine the correction factors using later in time hydrophone measurement data.

Abstract: A narrow band compensating beamformer for a receiving array that conforms some surface other than a plane and thus is, in general, three dimensional. The array comprises a number of sensing elements arranged in a non-planar pattern. Each sensing element has its output signal delayed or phase shifted as a function of the receiving angle by the beamformer in such a way as to produce an equivalent "projected planar array" in a particular direction. This arrangement has the same beam pattern in the selected direction as an equivalent planar array with its lower side lobe characteristics permitting the taking of advantage of well known, low side lobe shading techniques.

Abstract: A plurality of transducers, closely conforming to the surface of a low-drag ose, are baffle mounted in close pack configurations to eliminate grating lobes. The baffle assembly is mounted outside a pressure hull within a thin acoustically transparent fairing. A plurality of pressure compensators also attach outside the pressure hull. The cavity between pressure hull and fairing is filled with pressure compensating acoustic fluid. Larger portions of unused volume are first filled with a syntactic foam to minimize the amount of fluid required. The pressure compensators balance fluid pressure against external sea pressure to prevent fairing collapse. This array maximizes available nearby internal nose volume thus allowing beamforming electronics to be located within the pressure hull in close proximity to the array elements, connecting thereto via a plurality of short coaxial cables.