Acoustic Ray Tracing Comparisons in the Context of Geodetic Precise off-shore Positioning Experiments

ABSTRACT

The GNSS-Acoustics (GNSS-A) method couples acoustics with GNSS to allow the precise localization of a seafloor reference in a global frame. This method can extend on-shore GNSS networks and allows the monitoring of hazardous oceanic tectonic phenomena. The goal of this study is to test the influence of both acoustics ray tracing techniques and spatial heterogeneities of acoustic wave speed on positioning accuracy. We test three different ray tracing methods: the eikonal method (3D sound speed field), the Snell-Descartes method (2D sound speed profile), and an equivalent sound speed method. We also compare the processing execution time. The eikonal method is compatible with the Snell-Descartes method (by up to 10 ppm in term of propagation time difference) but takes approximately a thousand times longer to run. We used the 3D eikonal ray tracing to characterize the influence of a lateral sound speed gradient on acoustic ray propagation and positioning accuracy. For a deep water (⩾ 3,000 m) situation, frequent in subduction zones such as the Lesser Antilles, not accounting for lateral sound speed gradients can induce an error of up to 5 cm in the horizontal positioning of a seafloor transponder, even when the GNSS-A measurements are made over the barycenter of a seafloor transponder array.

KEYWORDS:

• Absolute position
• acoustic ranging
• geodesy
• seafloor positioning
• sound speed profile

Acknowledgment

The authors also thank the editor and reviewers for their comments and suggestions, which greatly improved the content of this article.

Additional information

Funding

The authors thank Jean-Yves Royer from the Laboratoire Géosciences Océan, University of Brest and the iXblue research and development team for their support. Some of this work was funded under the Région Bretagne CANOPUS FUI project. P. Sakic was supported by a PhD grant from the French Ministry of Research/University of La Rochelle.