Positioning model and analysis of the sailing circle mode of seafloor geodetic datum points

Sailing circle is a commonly used surveying pattern in determining the position of seafloor datum points. In this paper, the positioning efficiency of sailing circle mode is analyzed systematically. Firstly, the acoustic ranging non-differential positioning model considering the variation of sound velocity profile and the inter-epoch differential positioning model weakening the influence of systematic error are analyzed. Then, the positioning efficiency of non-differential and single-difference positioning models in sailing circle mode is analyzed, including the measurability of position parameters, the optimal measurement radius of different component position accuracy, the theoretical accuracy achieved, and the influence of ranging error on positioning parameters, et al. Theoretical analysis shows that in the standard sailing circle mode, to ensure the accuracy of different components of the datum position, different optimal measurement radiuses are derived, and the elevation component cannot be estimated with the pre epoch and post epoch differential positioning model. Both the simulation data and the measured examples show that the differential positioning model in sailing circle mode weakens the influence of the ranging system error, but also reduces the geometric observation intensity of the design matrix, which even lead to an ill-posed model and obvious weakening of the depth information estimation accuracy of the differential model.