Abstract
The Global Navigation Satellite System-Acoustic (GNSS-A) geodetic observation model needs to consider the spatiotemporal variation of sound velocity to achieve centimeter-level precision positioning. Existing research has mainly explored high-precision GNSS-A observation models from the perspective of the four-dimensional sound velocity field in the ocean. In fact, it is more directly effective to discuss the construction of high-precision positioning models from the perspective of the four-dimensional slowness field in the ocean. This paper investigates the impact of oceanic slowness variation on geodetic positioning. Under the assumption of a single-layer slowness field (SSF), a GNSS-A observation model with an attached slowness gradient is proposed. This model has significant advantages in simplifying the observation model formula and improving the efficiency of model solving. The proposed model and algorithm are validated through actual measurements and simulated GNSS-A data. The results show that the positioning accuracy in deep sea using the observation model with an attached slowness gradient can reach centimeter-level, comparable to the traditional sound velocity error compensation model. It has the same effectiveness as traditional sound velocity parameter estimation but with higher computational efficiency.