Retrieval of the dispersion curves of waveguide modes using shipping noise recorded by two vertical line arrays

A technique is proposed for estimating the dispersion characteristics of waveguide modes based on a comparison of the shipping noise recorded by two synchronized vertical line arrays. Using the proposed approach, an experimental study of the modal structure of a low-frequency sound field in a shallow-water waveguide (Lake Kinneret, Israel) with a gas-saturated bottom was carried out in a wide frequency band from 20 to 250 Hz. Bottom of the lake is rich in methane bubbles (~ 1% by volume) and, consequently, has low sound speed of the order of 100 m/s. The receiving system was two 27-m vertical arrays located at a distance ~40 m from each other in 40.4 m-deep water. The noise source, a research vessel, was moving along a straight line in the vertical plane containing the arrays up to 1 km range from them. The proposed approach made it possible to determine the frequency dependences of the phase speed for the first 12 modes, and these dependences turned out to be close to those for a waveguide with a perfectly soft bottom, except at the frequencies in the vicinity of the mode cutoffs.