Mode Coupling Due to an Underwater Ice Keel in a Broad Frequency Band

Numerical simulation is used to study the possibility of remote acoustic monitoring of underwater keels in ice-covered shallow-water waveguides. A statistically average hummock for the Arctic region is considered, with a keel draft of 8 m, located in a waveguide with a depth of 40 m. It is assumed that the ridge of the hummock is perpendicular to the acoustic track, the length of which is 10 km. A point broadband source and a vertical receiving array are used, which are necessary for extracting the mode amplitudes. It is shown that mode coupling due to the keel manifests itself quite distinctly in modulation of the mode amplitudes in a broad frequency band. A methodology for analyzing this modulation by constructing cepstrograms (spectrograms from the spectrum) is proposed. The cepstrograms reveal dispersion curves corresponding to pairs of coupled modes. Then, from the location of the dispersion curves on the cepstrogram, it is possible to estimate the location of the keel on the track.