Mid-frequency sound transmission in a deep ice-covered ocean at short and medium ranges

Abstract

A model of propagation and reverberation in a deep Arctic ocean and a tentative interpretation of ICEX16 data are discussed. The data subset used for analysis was collected by a NPS team in the Beaufort Sea (∼3650 m depth) on 12 March 2016 using mobile EMATT transmitters which were moving under the ice in circular patterns from Ice Camp SARGO that provided various combinations of source-receiver ranges (∼1–10 km) and depths (45–183 m). Transmitted waveforms were sequences of 60 s-long segments comprised of 57 s-long CW pulses at various frequencies (2800, 2900, and 3000 Hz) and 3 s-long 2300–3000 Hz LFM sweeps. Sound speed profiles measured during the experiment showed two shallow ducts, at 0–75 m and 75–250 m water depths. The model developed considers multi-path propagation including multiple reflections and scattering from rough interfaces. The model-based analysis allows examining the spatial and time-frequency structure of recorded arrivals and their sensitivity to variations in water stratification and acoustic parameters of ice and ocean bottom. Preliminary results of the ICEX16 data-model comparisons are presented. Suggestions are considered for environmental measurements to provide necessary inputs and ground-truth for the acoustic model. A potential for enhanced remote sensing capabilities and optimal configurations for future experiments are discussed. [Work supported by ONR.]