A Robust Method to Estimate the Coordinates of Seafloor Stations by Direct-Path Ranging

Abstract

The ranges derived from acoustic measurements between seafloor stations are relatively more accurate compared with those derived from the sea surface vessel transducer to the seafloor transponders, because measurements through mixed water layers will be affected by complex acoustic range errors. Coordinates of seafloor stations can be improved by the direct-path acoustic ranging. Systematic errors in acoustic rangings, however, will significantly deteriorate the accuracy of vertical coordinates. In order to mitigate the effects of these systematic errors (e.g., acoustic ray bending and sound speed variation errors in acoustic measurements on the seafloor station location parameters), the observation model needs to be finely constructed. First, a new observation model with acoustic ray bending and sound speed bias parameters is established. Then, using a seafloor geodetic network with four moored stations at a depth of about 3000 m in the South China Sea, the significance of the acoustic ray bending parameter is tested. The results show that (1) the acoustic ray bending parameter is significant at the 90% confidence level, which means that the acoustic ray bending error in the seafloor geodetic network is not negligible; (2) by estimating the coefficient of acoustic ray bending, the influence of the acoustic ray bending error on the vertical coordinate components can be significantly mitigated; our model improves the accuracy of the seafloor stations’ position with differences in the horizontal coordinate components less than 0.1 cm between the two-dimensional adjustment and three-dimensional adjustment, and also improves the vertical coordinate component to uncertainty less than 3.0 cm; (3) the relative movement between the moored stations is less than 50 cm, and the horizontal movement is larger than the vertical movement.

Keywords:

• Acoustic ray bending error
• direct-path acoustic ranging
• seafloor geodetic network
• sound speed variation errors

Author contributions

Xianping Qin undertook the formula derivation, model construction, calculation results analysis and drafted the manuscript. Yuanxi Yang guided the resilient function model construction, participated in the discussion of results analysis, and revised the manuscript. Bijiao Sun assisted in data preprocessing and manuscript revision.

Data availability statement

The datasets analyzed during the current study are not publicly available due to the management regulations of relevant organizations, but are available from the corresponding author on reasonable request.

Additional information

Funding

This work was supported by Wenhai Program of the S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao) (NO. 2021WHZZB1001), National Natural Science Foundation of China (Grant No. 41931076) and National Key Research and Development Program of China (Grant No. 2020YFB0505800).