Abstract: Target detection apparatus wherein a pulse of acoustic energy transmitted toward a target area of the sea bottom is reflected back to two spaced-apart receiver transducers. The sum and difference of the transducer outputs are obtained with the phase relationship therebetween being detected. An acoustic return from a target above or on the bottom will cause two returns to arrive at the receiver transducers at very slightly different times and at different angles thereby resulting in a phase relationship different than a return from the bottom. An output signal indicative of a target or no target condition is provided and is normalized so that its amplitude is independent of target strength.

Abstract: A forward look sonar system in which speed and direction of a sonar platform is obtained. Each acoustic transmission towards the target area over which the platform is traveling is comprised of a plurality of frequencies. A plurality of receiver beams is formed and each individual beam from one transmission is cross-correlated with its corresponding beam from a selected subsequent transmission to derive a delay value. The later received signal for each beam, for each frequency is divided into a plurality of small segments each of which is cross-correlated with a portion of the first return signal corresponding to the same frequency and beam. The cross-correlation functions for the plurality of frequencies for each particular segment are added together to obtain a more precise delay value. The correlation functions for each of the beams are added together and compared to derive a value for platform direction in the intercomparison period and the delay values are utilized to derive a velocity indication.

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: A dipole hydrophone which includes a piezoelectric bender bar having at the ends thereof two identical disks having high added mass and low actual mass, and a single mass at the center with low added mass and high actual mass. Support wires are connected to the unit at the bender nodes so that movement of the support causes no electrical output. Another configuration includes a piezoelectric bender disk having an annular ring near the edge portion thereof and a single mass at the center of the disk with the ring and central mass having the same relationship as the disk and central mass of the other embodiment.

Abstract: An electrodynamic sensor unit and a drive unit are attached to a member subject to vibration. The sensor unit provides a signal proportional to the vibration velocity, and this signal is utilized to govern the operation of the drive unit, which acts to reduce the vibration amplitude.