Underwater acoustic positioning system and method

In a system having a plurality of station keeping devices on or below the surface of the water, a method for an underwater device to determine its location, comprising:

• providing the underwater device with an acoustic signal time schedule, the acoustic signal time schedule indicating a time at which each station keeping device will emit an acoustic signal into the water;
• receiving by the underwater device an acoustic signal from each station keeping device, the acoustic signals being sent from each station keeping device according to the acoustic signal time schedule;
• calculating by the underwater device a distance between the underwater device and each station keeping device based upon the scheduled time for sending the acoustic signal and the time that the acoustic signal is received;
• and
• calculating by the underwater device of a position of the underwater device based upon the distances between the device to locate and the station keeping devices.

A system for determining the position of an underwater device to locate, comprising:

• a plurality of station keeping devices on or below the surface of the water, each station keeping device having:
• a GPS receiver for determining its position,
• a clock for keeping time,
• an acoustic transducer for generating acoustic signals in the water,
• a memory for storing an acoustic signal schedule, and
• a processor in communication with the memory and the acoustic transducer for generating acoustic signals in the water according to the acoustic signal schedule;
• at least one device to locate, the device to locate having
• a clock for keeping time,
• a memory for storing the acoustic signal schedule and a known position for each station keeping device,
• an acoustic transducer for receiving acoustic signals sent by the station keeping devices, and
• a processor configured to calculate the position of the device to locate underneath the water based upon the difference between the arrival time of the acoustic signals and the scheduled time for sending the acoustic signals;
• wherein each clock is synchronized, and each memory stores the same acoustic signal schedule.