Navigation System Integration and Evaluation for Precise Underwater Operations

This paper discusses a navigation system solution integrating inertial sensors and evaluates the application requirements for precise underwater operations dedicated to unmanned underwater vehicles. Accordingly, the systematic design of a high-grade inertial navigation module is described consisting of a fiber optical gyroscope based inertial measurement unit and additional position-independent auxiliary sensors for measuring velocity and pressure. In this context, modularization in the form of successive filter stages consisting of kinematic and kinetic Kalman filters was carried out in order to be able to realize a holistic approach. It is the combination of commercially available and process-specific components that creates a framework for enabling precise underwater operations. For performance determination of the system, evaluation tests were conducted using an unmanned surface vehicle in the port of Rostock. Besides the integrated solution, the impact of the auxiliary sensors on the autonomous motion state estimation was determined, simulating the navigation conditions during submerged operation. A high-precision Global Navigation Satellite Systems receiver served as a position reference. Finally, automated maneuvering tests were performed using an underwater vehicle in a restricted test tank, where the accuracy of the high-grade navigation module could be demonstrated even during long-term position update independent underwater operations.