Underwater vehicle positioning method using sound speed error estimation in conjunction with a motion compensation model

Accurate positional information is crucial for correlating data from underwater vehicles. Vehicle motion during the interrogation reception interval, along with challenges inaccurately measuring sound speed, degrades the performance of positioning solutions in two-way travel time measurements. This paper proposes a novel positioning method for underwater vehicles that incorporates sound speed error estimation with a motion compensation model. To mitigate the underestimation of position coordinates for moving vehicles, a time- based function is employed to fit the position coordinates during the interrogation reception. A solution for the coefficients of the basis function, derived from the ray acoustic travel model, is developed. Furthermore, this paper models the complex sound speed errors as time-varying sound speed profiles and incorporates them into the motion-compensated sound ray travel model. This results in a joint estimation framework for position fitting coefficients and sound speed errors, effectively resolving inaccuracies in motion model compensation and sound speed error estimation for real-time underwater vehicle positioning. Monte Carlo (MC) simulations demonstrate that the proposed method effectively compensates for the effects of vehicle motion and sound speed errors on underwater vehicle positioning. Sea trials confirm an average positioning error reduction to 3.03 m, significantly improving accuracy compared to existing models.