Underwater target detection apparatus

Target detection and enabler apparatus for an active acoustic guidance system of a torpedo having also azimuth and depth steering means, comprising in combination:

• a transducer, transmitter means for periodically energizing the transducer to project a pulse of acoustic energy, a receiver for producing electrical signals corresponding to resultant reverberation and echo-pulses, a discriminator circuit connected to the receiver for producing first and second discriminator signals, a reactance tube circuit for adjusting the frequency of the transmitted pulse, the first discriminator signal being adapted and applied to the reactance tube circuit to adjust the frequency of the transmitted pulse so that the frequency of the resultant reverberation as received is substantially the same as the center frequency of the discriminator, a demodulator connected to the receiver for demodulating said echo-pulse signals, a coincidence circuit, the second discriminator signals and the demodulated echo-pulse signals being applied to the coincidence circuit, said coincidence circuit adapted to produce therefrom a relay-energizing signal if the demodulated and second discriminator signals exceed predetermined minimum values and occur simultaneously, and an enabling relay connected to the coincidence circuit and energized by the coincidence circuit output signal for enabling the guidance system to assume control of the azimuth and depth steering means of the torpedo if the amplitude of the said output signal exceeds a predetermined value.

An underwater moving-target detection system for use in a propulsive craft, said system comprising, in combination, means for generating and repetitively projecting acoustic pulses adjustable in carrier frequency as generated;

• means for receiving resultant reflected acoustic energy including water reverberation, false-target echoes at substantially reverberation frequency, and moving-target echoes at differing frequencies;
• frequency discriminator means for converting said received acoustic energy to first and second discriminator signals, said first signal varying in both sense and magnitude, said second signal varying only in magnitude, in accordance with the frequency deviation of said received acoustic energy relative to a predetermined center-frequency;
• means for sampling said first discriminator signal immediately after projection of each acoustic pulse;
• means responsive to said sampled first discriminator signal and adapted to readjust said generated carrier frequency to such value that the frequency of resultant reverberation, as received, is substantially of predetermined fixed value;
• means for deriving, from said echoes, control signals having characteristics defining and varying in accordance with the direction from which the echoes arrive;
• control signal utilization circuits;
• an enabling relay adapted, when energized, to apply said control signals to the utilization circuits;
• demodulating means for converting received echoes to d-c pulses of corresponding amplitude;
• and coincidence circuit means having applied thereto said d-c pulses and said second discriminator signal and adapted to energize said enabling relay only when one of said d-c pulses exceeds a predetermined amplitude threshold and occurs in time coincidence with a second discriminator signal which exceeds another predetermined amplitude threshold.

An active-acoustic homing torpedo system comprising, in combination, means for generating and repetitively projecting acoustic pulses adjustable in carrier frequency as generated;

• means for receiving resultant reflected acoustic energy including water reverberation, false-target echoes at substantially reverberation frequency, and moving-target echoes at differing frequencies;
• frequency discriminator means for converting said received acoustic energy to first and second discriminator signals, said first signal varying in both sense and magnitude, said second signal varying only in magnitude, in accordance with the frequency deviation of said received acoustic energy relative to a predetermined center-frequency;
• means for sampling said first discriminator signal immediately after projection of each acoustic pulse;
• means responsive to said sampled first discriminator signal and adapted to readjust said generated carrier frequency to such value that the frequency of resultant reverberation, as received, is substantially of predetermined fixed value;
• means for deriving, from said echoes, steering control signals having characteristics defining and varying in accordance with the direction from which the echoes arrive;
• course and depth torpedo steering control circuits;
• an enabling relay adapted, when energized, to apply said steering control signals to the torpedo steering control circuits;
• demodulating means for converting received echoes to d-c pulses of corresponding amplitude;
• and coincidence circuit means having applied thereto said d-c pulses and said second discriminator signal and adapted to energize said enabling relay only when one of said d-c pulses exceeds a predetermined amplitude threshold and occurs in time coincidence with a second discriminator signal which exceeds another predetermined amplitude threshold.