Nature of waveguide invariant for multilayer sediment on New England shelf in 20–4000 Hz band

The waveguide invariant βmn (f), m,n = 1,2,…,N where N is the number of observed modes is inferred from sound emitted by merchant ships and from a towed mid-frequency source emitting CHIRP signals. The acoustic data were recorded on VLAs deployed in the New England Mudpatch during the Seabed Characterization Experiment 2017 in about 75 m of water. The received spectrograms show clear striation patterns out to 4 kHz. The seabed consists of about 12 m of mud over multiple sand layers extending down to about 300 m. Starting at β12(F) = ∞ at F about 25 Hz, βmn(f) is extended to 4 kHz. Below 500 Hz βmn exhibits a non-Pekeris behavior which results from the depth dependence of the multilayer seabed. Above 500 Hz the behavior of βmn begins to exhibit more of a Pekeris behavior, although there exist features that result from the finite thickness of the mud layer. A conclusion is that βmn (f) is sensitive to the geoacoustic structure over a large bandwidth, and thus has the potential to be utilized for remote sensing of the seabed with wideband sources.