An Underwater Gravimetry Method Considering Unknown Ocean Current Velocity Based on SINS/DVL/DG

  Abstract—Underwater gravity measurement systems typically consist of the strapdown inertial navigation system (SINS), the doppler velocity log (DVL), the depth gauge (DG), and other underwater sensors. Although SINS can provide continuous autonomous navigation parameters, the results obtained from pure inertial navigation diverge over time due to gyro drift and accelerometer biases during prolonged operation. Therefore, relying solely on SINS cannot meet the accuracy requirements for gravity measurements. The DVL can accurately measure the carrier’s velocity and compensate for SINS errors to obtain higher navigation precision. However, in areas with complex seabed topography or when the carrier operates far above the seafloor, the DVL-measured water-relative velocity does not reflect the true motion relative to the seabed. Such velocity errors severely degrade underwater positioning accuracy and consequently compromise gravity measurement quality. To address this issue, we propose a SINS/DVL/DG underwater gravity measurement model considering unknown ocean current velocity based on Cubature Kalman Filter (CKF). By exploiting the short-term stability of ocean currents, a nonlinear state equation is established incorporating attitude, velocity, and current velocity. Measurement equations are formulated based on velocity errors from the DVL’s bottom-tracking and water-tracking modes, respectively. The system state and covariance are updated via the third-degree spherical-radial cubature rule, enabling real-time estimation of the carrier’s attitude and velocity, as well as current velocity. After compensating for velocity errors, high-reliability gravity data are derived from the corrected navigation information. The proposed method was validated using sea trial data collected in a 500-meter-deep area. Results show that the estimated ocean current velocity error remains below 0.01 m/s, and the internal consistency of repeated gravity survey lines reaches 1.00 mGal. Compared to traditional integrated navigation approaches, the proposed method significantly improves positioning accuracy by effectively compensating for DVL water-track velocity errors, thereby delivering high-precision gravity measurements even under unknown ocean current conditions.

  Index Terms—underwater gravity, integrated navigation, effect of ocean current, inertial Navigation, internal accuracies

 

 

Fig.1 Flow chart of the SINS/DVL/DG underwater gravimetry method considering the unknown ocean current velocity

 

 

Fig. 2 Comparison chart of gravimetry results