Peter Gerstoft
Jean-Pierre Herm
SACLANT Undersea Res. Ctr., 19138 La Spezia, Italy
Taco van der Leij
Ctr. for Technical Geoscience, Delft Univ. of Technol., Delft, The Netherlands
The estimation of forward model parameters---geometric, geoacoustic, and ocean sound-speed---by the inversion of acoustic field observations is considered. During autumn '94 and spring '95 an exhaustive set of broadband acoustic data and environmental data was obtained over a shallow-water area in the Mediterranean Sea [Hermand et al., ``The Yellow Shark Broadband Inversion Experiments'' (to be published)]. In this paper, inversion results of a mildly range-dependent transect southeast of the Island of Elba are presented. The inversion is carried out from multitone data (in the frequency band 200--1600 Hz) received on a 62-m vertical array from a fixed acoustic projector deployed at different ranges (4.5--15 km). Hydrographic data measured during the acoustic transmissions and coring and seismic profiling of the sediments along the acoustic track are utilized to control and verify the inversion process. Global optimization through a directed Monte Carlo search based on genetic algorithms and the Bartlett objective function is applied. All geometric parameters are well determined and also a range-dependent geoacoustic model and the ocean sound-speed profile are estimated. The use of observations at multiple frequencies provides considerable stability for the estimated parameters.