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US 4,305,141 AGranted
Low-frequency directional sonar systems
AssigneeThe Stoneleigh Trust
InventorFrank Massa
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AssigneeThe Stoneleigh Trust
InventorFrank Massa
Estimating the term…
A portable sonar surveillance system is disclosed which operates in the audible-frequency region where low attenuation loss minimizes the power requirement for achieving long-range detection capability. A light-weight, high-power transmitting transducer array approximately 1 ft. diameter, which operates efficiently in the 4-6 kHz range, is utilized in combination with a novel tri-cardioid hydrophone receiving array whose diameter is only a few inches to achieve a bearing resolution of 5.degree.. The inventive system replaces enormous sized conventional low-frequency scanning sonar systems weighing tens of thousands of pounds. The disclosed system can be very effectively used as a long-range, light-weight "dunking sonar" for submarine surveillance patrol operations from helicopters or small patrol craft. The disclosed sonar system is economically practical for use in the 1 kHz frequency region, thus achieving ultra-long-range detection capability which cannot be obtained with conventional scanning sonar systems.
In combination in a directional sonar system for the detection of the presence and the location of the position of an underwater sound reflecting target, a sound transmitting transducer adapted for the generation of a tone burst signal lying within the audible-frequency range upon being supplied with a tone burst of audio-frequency electrical power, a source of audio-frequency power, electrical switching means connecting said source of audio-frequency power to said transducer, control means for operating said switching means, a plurality of directional receiving hydrophone assemblies characterized in that the receiving sensitivity S of each hydrophone assembly as a function of angle .theta. from its normal axis of maximum sensitivity is defined by the approximate relationship s=(1+cos .theta.) over an angle of approximately .+-.120.degree. from its normal axis, structural support means for mounting said plurality of directional hydrophone assemblies in an array with the axis of maximum sensitivity of each hydrophone assembly pointing 120.degree. apart in relative bearing from each other, said transmitting transducer characterized in that its horizontal dimension when operationally submerged underwater is less than two wavelengths of the radiated sound at the frequency of operation, said receiving hydrophone array characterized in that its horizontal dimension when operationally submerged under water is less than 1/2 wavelength of the received sound at the frequency of operation, a signal processor, electronic circuit means connecting the output of each directional hydrophone assembly to said signal processor, said signal processor characterized in that it includes means for comparing the ratios of the magnitudes of the output signal levels from each directional hydrophone assembly when said hydrophone array is activated by a sonar signal which is arriving from a direction whose bearing angle is unknown, and indicator means selectively responsive to the ratios of the magnitudes of said output signal levels from said directional hydrophone assemblies, whereby said indicator means indicates said unknown bearing angle.
In combination in a portable light-weight directional sonar system for the detection of the presence and location of the position of an underwater sound reflecting target, a sound transmitting transducer line array adapted for operation within the audio-frequency range below 15 kHz to generate an audio-frequency tone burst signal upon being supplied with a tone burst of audio-frequency electrical power, a tri-cardioid receiving hydrophone, means for mounting said tri-cardioid hydrophone in a fixed position relative to said transducer line array, said hydrophone mounting means characterized in that the axis of maximum sensitivity of each cardioid hydrophone element is displaced in azimuth 120.degree. from its neighboring cardioid hydrophone element, a source of audio-frequency power, electrical switching means for connecting said source of audio power to said transmitting transducer, control means for operating said switching means, a signal processor, electronic circuit means for connecting the output of each cardioid hydrophone element to said signal processor, said signal processor characterized in that it includes means for comparing the ratios of the magnitudes of the output signal from each of the three cardioid hydrophone elements when said tri-cardioid hydrophone is activated by a sonar signal arriving from a direction of unknown bearing angle, and indicator means selectively responsive to the ratios of the magnitudes of the output signal levels from the three cardioid hydrophone receiving elements, whereby said indicator means indicates said unknown bearing angle.
In combination in a portable light-weight directional sonar system for the indication of bearing and range of an underwater sound reflecting target, an explosive underwater sound source, means for activating said underwater explosive sound source, whereby a shock wave signal is generated by said underwater sound source, a tri-cardioid receiving hydrophone comprising three cardioid receivers mounted with their axes of maximum sensitivity displaced in azimuth 120.degree. from its neighboring cardioid receivers, a signal processor, electronic circuit means for connecting the output of each cardioid hydrophone receiver to said signal processor, said signal processor characterized in that it includes means for comparing the ratios of the magnitudes of the output signals from each of the three cardioid hydrophone receivers when said tri-cardioid hydrophone is activated by a shock wave signal which is arriving from an unknown bearing angle, and indicator means selectively responsive to the ratios of the magnitudes of the output signal levels from the three cardioid hydrophone receiving elements, whereby said indicator means indicates said unknown bearing angle.
Dependencies are inferred from the claim text.