Assessment of passive bottom loss estimation methods in the New England shelf break area

Proper knowledge of geoacoustic bottom properties can be critical for accurate acoustic propagation predictions in the ocean, particularly in shallow environments. Unfortunately, these properties are unknown in much of the ocean. This knowledge gap presents a need for measurement techniques that enable the inference of critical bottom properties in a timely, cost effective manner. One such approach, proposed by Harrison and Simons, exploits the spatial structure of surface-generated, mid-frequency ambient ocean noise to infer bottom loss in a region as a function of bottom grazing angle. This method, known as the Up-Down Ratio, is fully passive and necessitates only a vertical line array with sufficient resolution for the frequencies of interest. A second approach, introduced by Buckingham, utilizes passive noise correlation between two vertically-separated hydrophones for similar purposes. In this presentation, these passive methods will be employed to estimate bottom parameters from mid-frequency (2–4 kHz) MACOS glider measurements collected within the New England Shelf Break Area as part of the Seabed 2021 joint experiment. In addition to comparisons of the inferred bottom parameters, discussion will include the ease of implementation of the methods as well as robustness against real data-collection challenges such as array tilt and strong surface interferers.