Acoustic navigation and diving information system and method

A method for enabling an underwater object to determine its position, comprising:

• deploying a base unit with means for accurately determining the position thereof;
• deploying a remote unit with means for accurately determining the position thereof, at a location which is spaced from said base unit;
• emitting a tracking unit digital acoustic message from said underwater object;
• receiving said tracking unit message at said base unit;
• emitting a base unit digital acoustic response message from said base unit in response to reception of said tracking unit message, said message including data specifying the location of said base unit;
• receiving said base unit message at said object and marking the time of arrival to determine a first time delay between emitting said tracking unit message and receiving said base unit message;
• receiving said tracking unit message at said remote unit;
• emitting a remote unit digital acoustic response message from said remote unit a predetermined second time delay after reception of said tracking unit message, said remote unit message including data specifying the location of said remote unit;
• receiving said remote unit message at said object and marking the time of arrival to determine a third time delay between emitting said tracking unit message and receiving said remote unit message;
• and
• determining the position of said object from said first, second and third time delays and said data comprising said base unit and said remote unit messages specifying the locations of said base and remote units.

An acoustic navigation and communication system for underwater divers or vehicles, comprising:

• a base unit comprising means for accurately the position of said unit, a base transponder means for transmitting and receiving digital acoustic data messages via propagation through the water, wherein said transmitted messages comprise base unit position data specifying the position of said base unit;
• a remote unit spatially separated from said base buoy, said remote unit comprising means for accurately determining the position of said remote unit, a remote unit transponder means for receiving and transmitting digital acoustic data via propagation through the water, wherein said transmitted message comprises remote unit position data specifying the position of said remote unit;
• a plurality of tracking units whose underwater position is to be determined, each tracking unit comprising:
• a tracking unit transponder comprising means for transmitting tracking unit acoustic digital messages during preassigned time intervals unique to that tracking unit and means for receiving acoustic digital messages, said tracking unit digital messages identifying the particular tracking unit and comprising data indicating a last known position for said tracking unit;
• processor means for determining said tracking unit position in dependence on data received from said base and remote units specifying the respective positions of said units and propagation delays in the transmission of said acoustic messages underwater;
• a base station, comprising means for communicating commands to said tracking units and receiving tracking unit messages via said base unit, and means for processing said tracking unit messages to ascertain the location of each tracking unit.