Global navigation satellite system (GNSS) spoofing poses a significant threat to maritime logistics. Many maritime electronic devices rely on GNSS time, positioning, and speed for safe vessel operation. In this study, inertial measurement unit (IMU) and Doppler velocity log (DVL) devices, which are important in the event of GNSS spoofing or outage, are considered in conventional navigation. A velocity integration method using IMU and DVL in terms of dead-reckoning is investigated in this study. GNSS has been widely used for ship navigation, but IMU, DVL, or combined IMU and DVL navigation have received little attention. Military-grade sensors are very expensive and generally cannot be utilized in smaller vessels. Therefore, this study focuses on the use of consumer-grade sensors. First, the performance of a micro electromechanical system (MEMS)-based yaw rate angle with DVL was evaluated using 60 min of raw data for a 50 m-long ship located in Tokyo Bay. Second, the performance of an IMU-MEMS using three gyroscopes and three accelerometers with DVL was evaluated using the same dataset. A gyrocompass, which is equipped on the ship, is used as a heading reference. The results proved that both methods could achieve less than 1 km horizontal error in 60 min.

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This article proposes a novel initial bias estimation method using a trajectory generator (TG). The accuracy of attitude and position estimation in navigation after using the inertial navigation system/Doppler velocity log (INS/DVL) and INS/DVL/gyrocompass (IDG) for 1 h were evaluated, and the results were compared to those obtained using the conventional Kalman filter (KF) estimation method. The probability of a horizontal position error < 1852 m (1 nautical mile) with a bias interval > 400 s was 100% and 9% for the TG and KF, respectively. In addition, the IDG average horizontal position errors over 1 h were 493 m and 507 m for the TG and KF, respectively. Moreover, the amount of variation was 2 m and 27 m for the TG and the KF, respectively. Thus, the proposed method is effective for initial bias estimation of INS/DVL and IDG using micro-electro-mechanical system sensors on a constantly moving vessel.

The present paper shows a basic reseem ℃ h fbr Inertial Navigation equipment using MEMS (Micro Electro Mechanical Systems) sensors ． Usually ， GPS is used for setting a ship ' s position ． Gyro conlpass and magnet compass are used fbr deciding ship ' s heading． According to thζ recent techno1Qgical innovatiQn ， an inertial navigation system has potential to be the next navigation equipment ibr ships ． One of 皿 ost exciting technical advanoement is MEMS sensors ． MEMS devices overco 皿 e many of the featUres that have impended the adoption of inenial systems by many potential applications ， especially where cost ， size and pewer consumption have been geverning parameters ． It is concluded that it would be possible to make autonomous system using enly MEMS sensors ． Keywords ： M ， Sensor ， lnertia-Navigation ， (｝ yro， Accelera tiOn ， Turn rate

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