An Underwater Gravimetry Method Using Inertial Navigation System and Depth Gauge Based on Trajectory Constraint

Due to the errors of the accelerometer and gyroscope, the position and the velocity calculated by the inertial navigation system (INS) are divergent with time. We can normally estimate and compensate the errors of the INS using the underwater sensors. However, the underwater sensors such as ultrashort baseline (USBL) acoustic positioning system and Doppler velocity log (DVL) are challenged by the complex environment, which affects the reliability and the accuracy of data processing. From the gravimetry error equation, the horizontal position errors have little influence on the underwater gravimetry. Observability analysis indicates that the velocity error and the position error can be well estimated on the condition of only positional observations in the Kalman filter. Based on these, we proposed a novel method using the INS and depth gauge (DG) based on trajectory constraint without USBL and DVL. In this method, we considered to fit the track of the gravimeter to a straight line because the gravimeter maintains uniform motion in the measuring line and take the fit line and the depth measured by the DG as the observations to correct the errors of the INS. We constructed an underwater experiment in 2019 to test the novel method. The test results showed a repeatability from 1.24 to 2.03 mGal for the space resolution of 200 m. The new method can acquire a good accuracy and can be applied to the gravimetry data processing.