US Patent 7362655 Time-synchronous acoustic signal ranging system and method

This is an underwater acoustic ranging system for determining a range to a target object. An acoustic receiver is provided for detecting acoustic energy and determining an angle of arrival of said acoustic energy in at least one plane. An acoustic transmitter transmits an acoustic energy pulse. A receiver clock joined to the receiver, and a transmitter clock is joined to the transmitter. Acoustic energy is transmitted at a synchronized time. Range can be calculated based on the transmit time, the receive time and the reception angle. The system can also include a means for synchronizing the clocks.