Abstract:

Low-frequency (350-450 Hz), shallow-water propagation measurements were made in several sites in the southern Barents Sea in June 1991 using combinations of broadband signals. The experiment used a two-element vertical source array to transmit the signals, and an omnidirectional source/receiver echo-repeater system to retransmit the signals back to a horizontal line array near the original source location. (All platforms moved at 3 kt.) Measures of two-way signal spreads were collected over a variety of ranges (5 to 50 km) and environmental conditions. Considerable time spreads (up to 1 s) were observed with a characteristic constancy of peak values over the length of the spreads, while analysis of PRN and CW data showed that spectral spreads were confined to very low Dopplers. Furthermore, selected sets of signals were time reversed prior to echo repeating to measure the ability of this highly-spread environment to refocus acoustic energy back to the original source location. Simulations of two-way temporal signal dispersion using the OASES and ORCA models for both time-forward and time-reversed retransmissions are presented and compared to data results for several representative cases. [Work supported by ONR and NAWC.]