Glider-based passive bottom reflection-loss estimation: Proof of concept

This study presents the proof of concept, based on data collected by a flying glider, for extending the capabilities of autonomous underwater vehicles to the passive measurement of the seabed reflection loss, an important contributor to the transmission loss in shallow water scenarios. During the GLISTEN 15 experiment, a Slocum glider was equipped with an advanced acoustic multi-channel payload coupled with a nose-mounted eight-element vertical line array of hydrophones. By processing the ambient-noise field generated by wind and breaking waves at the surface, recorded while the glider is quietly hovering over the seabed, the system provides an entirely passive, in situ measurement of the bottom power reflection coefficient as a function of frequency and grazing angle. The theoretical foundations and the algorithms for processing the data are summarized and applied for the first time to data collected by a linear array mounted on a flying glider. The results are compared to those obtained by arrays moored in the vicinity of the glider during the same experimental campaign. The possibility of recovering the layering structure of the bottom by passive fathometry is also discussed.