Yellow Shark Spring 1995: Inversion results from sparse broadband acousticmeasurements over a highly range-dependent soft clay layer

In May 1995, SACLANTCEN performed broadband(200;800 Hz) acoustic measuremen ts in the Giglio basin off the coast of Italy as part of the Yellow Shark i nversion experiments. In this paper, inversion of sparse, broadband transmi ssion loss (TL) measurements is investigated to determine bottom properties in strongly range-dependent (RD) situations,commonly encountered in shallo w water. The data are from the Elba-Formiche transect where water depth var ies from 65 m at the acoustic projector location, to approximately 120 m at the 4-element vertical arrays deployed at ranges of 8, 16, 24, 32, and 40 km along the transect. The experimental site has a soft clay-layer bottom w hich varies in thickness from 3 to 10 m with a:a sound speed less than the water column. A modal analysis including coupling effect is given to explai n:the frequency bands for which high TL was observed as a function of range and depth. The TL measurements were inverted by matching the RD fields wit h model results. Using parabolic equation modeling, bottom geoacoustic para meters were varied in a marching search to fit the TL:measured at the five ranges. The experimental results demonstrate that RD bottom properties such as sound speed and thickness of the slow clay layer can be obtained from b roadband TL measurements sparsely distributed in range and depth. [S0001-49 66(99)04907-3].