Resilient observation models for seafloor geodetic positioning

Acoustic positioning of the seafloor geodetic network is subject to the complex ocean environment. The measurements are strongly affected by time-varying and location-varying ocean physical phenomena. At first, the differential and undifferential acoustic positioning modes are analyzed. Then, a simple resilient observational model with range bias and time bias parameters is established. After solving the location parameters of the seafloor stations together with the range bias and time bias parameters, a resilient observation model with periodic error parameters is proposed. Taking the advantage of the systematic errors implied in the residual series, a piecewise second-order polynomial was introduced to fit the residual series. The corresponding calculation steps are designed. A real seafloor geodetic network with five stations was deployed at a depth over 3000 m in the South China Sea in July, 2019, one of which was shelter-fixed and the others were rope-fixed which were called underwater auxiliary navigation beacons. The cross-configuration measurement lines were employed for the seabed station and the underwater auxiliary navigation beacons. More than 26 measurement hours of GNSS/acoustic ranging observations were collected. The results show that the resilient observational model with periodic error terms compensates for the systematic errors of the acoustic ranges very well, with the square root of variance of the coordinate component better than 0.4 cm and the root mean square errors (RMSE) of the one-way slant range residuals better than 11 cm.