The acoustic homing system of an unmanned arctic research submersible

The underwater acoustic homing system described here is used to lure an arctic research vehicle back to its recovery hole. It makes use of a 28 kHz beacon which emits 4 ms pulses four times per second. The receiver in the vehicle employs two transducers spaced 3/8
\lambda
apart which are used for bearing detection, and a third omnidirectional transducer used for sense detection. Phase comparison is employed in bearing calculation and time difference in sense determination. The circuit also includes logic which rejects impulse noise and requires: a pulse amplitude > -100 dBV, 3 ms pulse duration, pulse rate of two to five pulses/sec, five out of eight valid pulses, and a stationary source (phase rate of change < 10 degrees/sec). The homing range of this system is over 5000 yd.