BASIC STUDY ON POSITIONING OF AUTONOMOUS UNDERWATER VEHICLE BASED ON ACOUSTIC RANGING FROM ONE REFERENCE DEVICE

An autonomous underwater vehicle (AUV) equipped with some navigational devices, such as an inertial navigation system (INS), a Doppler velocity log (DVL), and a depth sensor. This integrated system is typical and accurate, however, have drift error in position output. Then an acoustic positioning, which is one of absolute positioning, is necessary to compensate the drift error. As acoustic positioning, ultra-short baseline (USBL) is frequently used, however, not accurate especially in deep water. Long baseline (LBL) is very accurate, however, spends much time to operate. In this paper, acoustic positioning method of AUV based on ranging from only one reference device is considered with simulations. One-way travel time (OWTT) is measured for ranging assuming use of chip scale atomic clock (CSAC). And the ranging signal is continuous and modulated direct sequence spread spectrum (DSSS). Ranging is executed at each symbol peak, then period of the ranging is very small. In process of the method, the drift error of position output of the INS is estimated with extended Kalman filter (EKF). Simulation with two models, constant-position-error, and constant-velocity-error models, were performed. The later was obviously unstable. Circular cruising track of the AUV makes the estimation more stable. Moreover, when the AUV cruises near the reference, the estimation is more stable. It may good that at final phase of descending of the AUV, the AUV cruises near the seabed and spirally, and the estimation process may be performed stably.