Low frequency portable lightweight sonar systems and their method of deployment for greatly increasing the efficiency of submarine surveillance over large areas
A novel configuration of a low-frequency lightweight sonar system is described comprising a coaxial assembly of a transmitting transducer and a directional receiving array contained within a cigar-shaped streamlined cylindrical housing less than 1 ft. diameter which operates in the 3 to 4 kHz frequency region and achieves submarine target detection ranges in the order of 20,000 meters with a bearing accuracy within 2.degree.. The small cylindrical streamlined structural assembly results in a very great reduction in drag resistance while it is being towed underwater at high speeds as compared to conventional sonar domes which must be an order of magnitude larger in diameter to accommodate the larger conventional scanning sonar transducers which are several wavelengths in diameter at the operating frequency. The enormous reduction in drag resistance and the novel method of deployment permits the described low-frequency lightweight sonar system assembly to be pulled through the water at very high speeds by small patrol craft or helicopters to achieve very effective long-range low-cost high-speed sonar surveillance of very large areas of the sea.
A process of acoustic emission for sonar with a separate emission array from the receiving array. The emission array has the shape of a linear acoustic array and can either be towed simultaneously with linear acoustic receiving array or be suspended from a helicopter to form a "dipping" type sonar. Detection using this type of sonar is facilitated by increasing the sound level via the directivity index, while reducing the level of reverberation originating from the bed and from the surface of the sea.
A compact, modular sonar assembly for use on the bow of a ship having separate transmitting and receive arrays confined within a single acoustic housing. The narrow and compact design fits much better into the hydrodynamically desirable bulbous bow deign than the typical bow dome sonar design and achieves good performance at a low cost with reduced size and weight.
