An in-situ method for the correction of initial position error of an autonomous underwater vehicle near sea floor

This paper presents an in-situ correction method to compensate the initial position error of an autonomous underwater vehicle (AUV) near sea floor. AUVs generally have an inertial navigation system assisted with auxiliary navigational sensors, such as Doppler velocity log, and/or acoustic positioning systems. Since inertial navigation systems show drift in position without the bottom reflection of DVL, acoustic positioning systems are needed to set initial position. The main concept of the correction method is this: When the AUV arrives near sea floor, the vehicle horizontally moves around in circular mode, while the USBL transceiver installed on a surface vessel gathers the AUV´s position. After acquiring one data set, a curve fitting method is adopted to find the center of the AUV´s circular motion, which is transferred to the AUV via an acoustic telemetry modem (ATM). The proposed method can reduce the intrinsic position error of the USBL. The proposed method is robust to the outlier of USBL, and it is independent of the AUV motion that may induce position error due to the time delay of the data transfer with the ATM. Monte Carlo simulation was conducted to verify the performance of the proposed calibration method.