Abstract:

In May 1995, Saclant Centre performed broadband (200--800 Hz) acoustic measurements near Elba Island off the coast of Italy as part of the Yellow Shark '95 experiments. The experimental site has a soft clay layer bottom that varies in thickness from 3 to 10 m and has a sound speed less than the water column. The data presented here are from a range-dependent transect where the water depth varies from 67 m at the source location to approximately 120 m at the vertical arrays located every 8 km from 8 to 40 km from the source. The vertical arrays were sparsely populated with just four hydrophones positioned throughout the water column. A modal analysis is given to explain the frequency bands where high transmission loss is observed in the data. The observed data are inverted by matching the fields with modeling results. That is, using range-dependent modeling, the bottom type was varied in a search to fit the large-scale features of the modeled and observed transmission loss data. The results show that large-scale features can be used to identify some properties of the bottom such as the existence and thickness of the slow clay layer.