Pseudo-Doppler resonance phenomena in continuous wave scattering from evolving intermediate bubble plumes

An analytic expression is found for the scattered spectrum that is produced when a model dynamic bubble plume is ensonified by a continuous wave (cw) signal. The plume is of the ‘‘intermediate’’ type—with an interior sound speed well below that in the surrounding water—and thus exhibits sub-kHz internal resonances. These are assumed to be of a simplified Breit–Wigner type and their time dependence is shown to produce Doppler-like phenomena in the scattered spectrum. These ‘‘pseudo-Doppler’’ features are related to the parameters that specify the target plume’s time evolution. Conclusions are supported by comparison with the results of an exact numerical scattering calculation.