Mid-frequency propagation and reverberation time series ina deep ice-covered ocean: Modeling and data analysis

Mid-frequency (3.5 kHz) pulses (5 pings, 5 s-long, one per minute) were radiated by an omnidirectional source of opportunity in a deep (3 km) Arctic ocean at 30m depth under ice during the ICEX14 experiment, ALAS component [Williams et al., IEEE-JOE 43, 145–159 (2018)]. Data analysis and modeling results are presented for normalized (re source level) acoustic intensityreceived by an omnidirectional hydrophone located at a 719 m distance from and the same depth as the source. Received time series showed a clear direct blast signal followed by an about 30 s-long reverberation coda. Modeling of the under-ice propagation shows that magnitude of the direct signal is strongly affected by presence of a weak near-surface (within 50 m depths) acoustic channel and by reflectivity of the ice, controlled by its physical properties and acoustical parameters, particularly the ice layer thickness. Analysis of the reverberation coda shows effects of reflections and scattering from rough and/or heterogeneous bottom, as well as reflectivity of the ice layer. Some other effects that may be caused by variability of the sound speed profile and absorption in water are considered as well. Possibilities of inversions for water column, bottom and ice parameters based on this and similar experiments are discussed. [Work supported by ONR.]