Underwater Acoustic Positioning System

Sonatech proposes to continue the development of the operational concept for an underwater “GPS-type” acoustic positioning system (UWAPS), to be deployable from surface craft or hovering helicopter, and to provide multiple users the ability to navigate with GPS precision underwater. UWAPS has application for unmanned underwater vehicles (UUV), SEAL delivery vehicles (SDV), and diver-held Hydrographic Mapping Units (HMU) and Underwater Imaging Systems (UIS). UWAPS will consist of a field of autonomous acoustic transponder sensors transmitting periodic time-synchronized spread spectrum signals. Following deployment, the transponder array will automatically self-calibrate to establish precise transponder XYZ positions. Geodetic cross referencing will be accomplished using GPS/Acoustic Relay Units installed initially on the ocean bottom and released under acoustic control of the deployed transponder array, to provide a one-time unattended dual position fixing (acoustic and GPS) at the ocean surface. Once automatic calibration has been completed, User equipment will passively monitor transponder transmissions, and convert time differences of arrival to XY positions in real time with an accuracy of better than 2 meters. User depth will be measured directly using pressure sensors. Each transponder will transmit its own position data periodically, so users need no prior knowledge of array placement parameters. Once transponders are deployed, no further surface presence or equipment is needed for system calibration or operation. Phase I investigations included: a. Detailed definition and design of all acoustic signals required b. Determination of the optimum method of transferring transponder coordinates to user equipment via acoustic telemetry. c. Define optimum battery chemistry and electronics package size to support all performance requirements while minimizing physical size and handling requirements. Phase II objectives include the design, fabrication and field testing of prototype transponder hardware to demonstrate performance of data telemetry functions that are critical to autonomous array self calibration.