Abstract: In order to sense the presence of sound in a remote underwater location, a neutrally buoyant reflector (20) is deployed underwater, and a laser (12) disposed at a remote location aims coherent light at the reflector (20). A detector (24) senses the coherent light reflected from the reflector (20) and compares it in phase with coherent light split from the outgoing beam. The system then provides an indication of the presence of sound by, for instance, amplifying the result of the phase detection to a speaker (26).

Abstract: This invention is a hydrophone (element) sited beamformer which is coupled to an array cable of a horizontal line array. A hydrophone-sited beamformer is coupled to each hydrophone in the array. The element-sited beamformer directly forms beams from the data detected by the hydrophones by delaying and selecting some of the hydrophone detected data and summing this data with the proper shading value.

Abstract: An ambient sea noise elimination system is disclosed in which the outputs of a directional hydrophone and an omnidirectional hydrophone are filtered and summed such that the effective receiving pattern below approximately 300 Hz is a vertically oriented dipole pattern having a null in the horizontal direction and such that the effective receiving pattern above 300 Hz is a cardioid having its null either pointing upwardly or pointing downwardly in a vertical direction. The option of simple omnicoverage at the high frequencies can also be easily implemented. This system thus takes advantage of the discovery that ambient sea noise under 300 Hz primarily travels in a horizontal direction whereas ambient sea noise above 300 Hz generally travels in a vertical direction.

Abstract: 1. In a method for communicating information between a submerged vessel and a buoy, the improvement comprising the steps ofA. allowing said buoy to assume substantially the same horizontal velocity as the water in which it is floating,B. feeding out a communication cable interconnecting said buoy with said vessel at substantially the rate at which the distance between said vessel and said buoy increases,C. destroying said buoy upon command, andD. releasing the fed-out cable from said vessel.

Abstract: Discrimination of long range targets from short range targets is provided by generating a vertical dipole beam and a narrow uni-directional horizontal beam which may be steered. Targets in the dipole beam are short range targets whose acoustic signals arrive at angles to the horizontal plane, whereas long range targets are those in the horizontal beam, since acoustic signals from long range targets come in on the horizontal plane.

Abstract: A hydrophone array system comprising a plurality of hydrophones fastened to a cable is deployed beneath the sea in a substantially horizontal straight line. A small powered thruster fastened to one end of the cable urges it in a first direction and this urging is resisted by a member, such as a drogue or an anchored subsurface float, fastened to the other end of the cable. Individual signals from each of the hydrophones are conducted to the surface where they are processed and transmitted by a radio link to a nearby aircraft or surface vessel. Beam forming and analysis is performed aboard the aircraft or surface vessel.