Prediction of sound propagation in the ocean is generally performed by assuming a time-invariant environment. However, the ocean changes in time, and the question is how this variability affects sound propagation. In May 1997 SACLANTCEN performed an experiment south of Elba in the Mediterranean Sea with the aim of investigating time-dependent effects of the ocean on sound propagation in shallow water. Three fixed propagation paths between a moored source and three vertical arrays were considered. Linear Frequency Modulated (LFM) signals covering a frequency band of about 7.0 kHz were transmitted every 1 minute for 36 h. Extensive measurements of the environmental parameters were performed during the acoustic measurements in order to correlate the environmental and acoustic variability. A measure of the time stability of the propagation channel as a function of range and frequency is obtained which, in turn, defines to what accuracy it is possible to predict sound propagation in a time-varying ocean channel.
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