An integrated navigation systems for underwater vehicles based on inertial sensors and pseudo LBL acoustic transponders

This paper presents an integrated underwater navigation system for underwater vehicles using inertial sensors and range sonar. We supposes that two acoustic transponders, called pseudo long baseline (LBL) system, are installed at two reference stations on sea bottom or below surface and/or ice. The navigation system is based on a strap-down inertial measurement unit (SD-IMU) mounted on an underwater vehicle and assisted with auxiliary navigation sensors, such as Doppler velocity log (DVL), depth, and heading sensors. Range measurement transducers are additional auxiliary navigation sensors. Using the two range measurements, the proposed navigation system will be able to improve the performance of conventional IMU-DVL navigation systems for long-time operation of underwater vehicles, and useful even without DVL information. An extended Kalman filter was adopted to propagate the error covariance, to update the measurement errors, and to correct the state equation when the external measurements are available. Simulations were conducted with the 6-d.o.f. nonlinear numerical model of an AUV in lawn-mowing survey mode under current flow condition. Navigation performance is surveyed for the cases when the bottom reflected DVL information is unavailable. Simulations illustrate the effectiveness of the integrated navigation system assisted by the additional range measurements and robustness on initial position error.