Abstract: An improved system is disclosed for calibrating acoustic pressure-sensitive transducers, particularly hydrophones, down to frequencies in the sub-Hertz range. A transducer under test and a reference transducer, both electrically connected to a voltage measuring device, are mounted in aligned proximity to each other upon a pivotal rocker arm immersed in a water tank. A cam and follower unit driven by a motor oscillates the rocker arm so that the transducers are moved through a vertical displacement equivalent to the desired fluctuation of hydrostatic pressure. As a result, calibrations down to 0.01 Hz are achieved.

Abstract: A sonar fish counter, primarily for counting salmon migrating in streams and for providing a separate count of king salmon, includes a narrow beamwidth side-scanning sonar transducer directed to insonify a volume of water in the stream directly above a mechanical beam which serves as an artificial bottom. The transducer transmits pulses of short duration such as 100 microseconds at regular intervals. After a delay following a transmitted pulse, a receiver is enabled to receive echo signals from any fish crossing the artificial bottom. During the period the receiver is enabled, a ring counter separates the return echoes on the basis of the return time from respective sectors of the bottom structure, and these returns are separately counted for each sector so that the counts may be displayed or printed separately.

Abstract: A sonar system for positive identification of certain resonant body targets such as mines. Two acoustic signals of different frequencies are transmitted toward the target and the acoustic returns are separated into the component frequencies, detected, and thereafter subtracted from one another. A signal, above a threshold value, resulting from the subtraction is indicative of a resonant body target and the indication is displayed and/or recorded.

Abstract: An ultrasonic rangefinder system for use in either an ultrasonic rangefinder camera or a general purpose ultrasonic rangefinder designer's kit provides a plurality of automatic sonic rangefinder functions when embodied in the photographic rangefinder camera while at the same time accommodating independently established control functions overriding the automatic functions when the rangefinder is utilized as part of the general purpose sonar rangefinder designer's kit.

Abstract: A towable, flexible electrode for high density electrical current transfer to sea water is characterized structural improvements including use of hard drawn aluminum wire and a rotatable and slideable aft slip ring to avoid "bird caging", and towing and electrical connectors having a first portion fixed to the electrode and presenting a boss, and a lug portion having a body with a bore receiving the boss and pinned thereto. The electrode features an optional insulating tube for moving the effective length of the electrode rearwardly of a towing platform.

Abstract: A sonar receiver comprises an inwardly curved reflector arranged to direct received sonar signals onto a transducer system. The transducer system comprises an array of transducers distributed over an inwardly curved path facing the reflector. Each transducer is responsive to sonar signals received from a particular direction to provide an output signal indicative of a reflecting object, the amplitude of which signal is related to distance of the reflecting object.

Abstract: An ultrasonic transducer which is suited to be placed in the place exposed to water, comprises an ultrasonic vibrator which transmits and receives ultrasonic wave, a horn which imparts directivity to the ultrasonic wave and a bent wave guide which connects the ultrasonic vibrator and the horn, and a reflecting plate which is provided in the bent portion of the wave guide for guiding the ultrasonic wave into the horn or the ultrasonic vibrator. According to the ultrasonic transducer of the present invention, the ultrasonic vibrator can be positioned above the horn when the horn is horizontally disposed. Therefore, the ultrasonic vibrator is not splashed with water entering from the horn.

Abstract: A circuit arrangement for forming a succession of group signals in the ranging art from received signals originating from an array of adjacent signal receiving transducers, each successive group signal being associated with a respective group characteristic and being based on the signals received by a respective group of adjacent transducers forming part of the array. The succession of group signals is processed to form a representation of the mean, or average, value of a predetermined number of successive group signals, and a representation of the ratio of the value of one of the group signals of that predetermined number of signals to the mean value is produced.

Abstract: An undersea communications system provides for improved data transmission pabilities. Two separate sources of information respectively modulate the upper and the lower sidebands of an acoustic carrier. The discretely modulated sidebands are simultaneously transmitted without the acoustic carrier or the acoustic carrier can be added to allow asynchronous or synchronous demodulation and use of the two modulating informations. Separation of the information in the two discretely modulated sidebands is assured by shifting the modulating information to ultrasonic regions and filtering out upper and lower sidebands of modulating information. Next, the shifted sidebands are modulated by an acoustic carrier which, optionally, is transmitted along with the discretely modulated upper and lower sidebands. A phase locked loop in the receiver portion assures synchronous demodulation or a crystal oscillator allows asynchronous demodulation of the discretely modulated upper and lower sidebands.

Abstract: An acoustic telemetry system and technique are disclosed for remotely meaing the underwater depth and descent rate of a hydrographic package. Analog signals indicative of hydrostatic pressure exerted on the package and related to its underwater depth are periodically sampled and converted to an N-bit digital word representative of the value of pressure. Each bit of the digital word operates one of a plurality of tone generators of different acoustic frequencies in a narrow band, and the outputs of the tone generators are combined with a reference tone continuously generated to permit resolution of Doppler shifts. Acoustically projected through the water to a remote hydrophone, a composite signal representative of the combined tones is corrected for Doppler shifts by translating the frequency of the signal in accordance with shifts detected in the reference tone.

Abstract: A new circuit is added to the old electrical circuit including two electrodes underwater positioned very close to a gas exhausting gun gaseous exhaust such as an air gun, wherein the exhaust from the firing gas exhausting gun momentarily blows away the conductive sea water from one or both of the electrodes to produce a high voltage pulse due to the large increase in resistance in the circuit indicating the precise moment of firing of the gas exhausting gun.This new circuit added to the above circuit is a circuit polarity reversing circuit which includes particularly a positive current generator, a negative current generator, and a sea ground for forming a third electron source when any of the two electrodes becomes defective, thus forming a fail-safe system.

Abstract: The present invention is directed to a detection system which forms reception beams successively in a series of angular directions. The detection system comprises receiving means for receiving incoming signals in such a manner that the frequency of the incoming signals is varied in accordance with the Doppler effect, and a matched filter for pulse-compressing output signals from said receiving means, with output signals from said matched filter being displayed in an indicator.

Abstract: A fish sonar is capable of detecting ultrasonic waves from a desired direction by shaping the waveforms of the outputs of a pair of vibrators spaced apart by a certain distance, and detecting a delay of the output from one of the vibrators with respect to that of the other of the vibrators so as to detect the direction of the ultrasonic waves coming to the pair of vibrators and to delay the output of the other of the vibrators with respect to the output of one of the vibrators.

Abstract: A sonar array wherein the capacitance associated with the hydrophones of the array are utilized as shunt elements in an artificial transmission line in order to form an acoustic beam. Series inductance elements to the transmission line are variable with d.c. current flowing through coils wound about a magnetic core about which coils forming the series inductance of the line are also wound, thus permitting the sonar beam to be steered to any desired position.

Abstract: The output of an auxiliary sensor, such as a magnetometer or metal detector, is recorded along side a sonar trace record, such as from a side scan sonar or sonar sub-bottom profiler, using the same recorder mechanism. In one embodiment, the added information permits correlation on the same chart between sonar generated impressions and local magnetic field disturbances such as produced by magnetically susceptible objects located on or below the seabed. The sonar record is typically provided as a series of adjacent scan lines, intensity modulated in accordance with the intensity of a received sonar echo. A conversion circuit transforms the output of the auxiliary sensor into a format consistent with the sonar scan trace whereby the sensor output is directly reproduced as a part of the sonar trace record, typically at a peripheral edge portion where the sonar image is absent.

Abstract: A sonar device for use on a boat to indicate the depth of water on a digital display, including a transducer positioned in the water to transmit bursts of sound energy and for receiving echo energy reflected from the bottom, at least one variable gain receiver stage for amplifying the echo signals received by the transducer, a microprocessor for processing the amplified received signals to supply appropriate control signals to the digital display to indicate depth as a function of time required to receive echo signals, a means of controlling the gain of the receiver stage including a means with the microprocessor of supplying a plurality of paralleled output digital signals indicative of the required gain, means for converting the digital signal output to an analog gain control signal, and circuit means for applying the voltage gain control signal to the sonar receiver.

Abstract: An amphibious end plug gauging device and method for determining the axial location of nuclear fuel element end plugs within or without the upper tie plate of a fuel bundle. The gauging device is maneuvered toward an underwater fuel bundle in a reactor service pool and its tip inserted in a preselected tie plate shank hole to engage the end of a fuel element in the bundle. The position of the fuel element relative the upper surface of the tie plate is registered on a dial indicator.

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 apparatus and method of transmitting and receiving information underwa assure improved performance characteristics. Modulating a carrier and appropriately filtering it allows the transmission of only single sideband signals or a carrier along with single sideband signals to increase the range at reduced power consumption levels. Demodulating incoming signals can be done synchronously (when the carrier is present) or asynchronously (only single sideband signals) to extract the information. When a number of carriers are modulated and, simultaneously, are transmitted and received, the system's reliability is enhanced.

Abstract: A method and apparatus are described for holographically generating visual representations of acoustical characteristics of sound sources. A planar array has a lattice of microphone receiving points are disposed such that evanescent wave energy from the sources is detected along with propagating wave energy. The microphone outputs are sampled, resolved into phase and amplitude components, digitized and subjected to fast Fourier transform operations to provide computer graphic display means with holographic reconstruction parameters corresponding to the sources under analysis.