Underwater position-fixing using digital acoustic communication techniques

This thesis describes an intelligent underwater acoustic system that allows the positions of several divers or Remotely Operated Vehicles (ROV) to be tracked in three-dimensional space and to telemeter the co-ordinates to a remote receiver at the surface. The positions are fixed using three randomly deployed seabed transponders that may be described as intelligent. The transponders fix their own relative positions and the position of the surface receiver, usually a vessel, by an exchange of coded acoustic pulses. These positions can be related to a differential GPS system at the surface if absolute coordinates are required. An underwater acoustic positioning and communication system can provide a vital navigation aid for a diver and surface supervisor. Often underwater positioning systems only provide the surface supervisor with diver's positions, with the diver navigating from voiced instruction via an acoustic or wire link communication. In the system described the divers each know their own position from a wrist-worn computer with a backlit graphical/numerical display. As well as the current position, the display can show the track from the beginning of the dive, the location of the surface vessel and the instantaneous position of the other divers. [Continues.]