This paper presents an underwater navigation system for underwater vehicles. The navigation system consists of an inertial measurement unit (IMU) and a Doppler velocity log (DVL) accompanying magnetic compass and depth sensor. A navigational system model is derived to include the scale effect of the DVL and bias errors of the inertial sensors. Indirect feedback Kalman filter is used in this paper, where the measurement equation is composed of the navigational state errors and system parameters. This paper demonstrates the effectiveness of DVLaided inertial navigation system through simulation and experiments. The tracking error of the navigation system is less than 1.0m for 10 minutes run from rotating arm test.
Since the radio wave cannot pass through the operating environment of underwater vehicles, acoustic positioning systems such as LBL (Long baseline), SBL (Short baseline), and USBL (Ultra short baseline) are widely used for underwater vehicles (Milne, 1983). These acoustic positioning systems have no accumulative error, while they have high frequency error and the update rate of them is usually very low. In general, LBL system is the widely used positioning system for its reliability, but we have to install acoustic sensors at the pre-determined position on the sea bottom, and the working range is limited by the position of the deployed sensors. On the other hand, USBL system can be used conveniently for the tracking and monitoring of far reaching AUVs, however the position accuracy is rapidly deteriorated as the sensing distance increases. Therefore, USBL is hard to be used alone for the positioning and control of underwater vehicle (Trimble, 1998). Inertial navigation systems are widely used for navigation, guidance and control of vehicles in land, air and at sea, because those are small and self-containable in mobile vehicles.