GEOACOUSTIC SEA-FLOOR EXPLORATION WITH A TOWED ARRAY IN A SHALLOW-WATER AREA OF THE STRAIT OF SICILY

Acoustic propagation in shallow water is greatly dependent on the geoa coustic properties of the seabottom, This paper exploits this dependen ce for estimating geoacoustic sediment properties from the bottom acou stic returns of known signals received on a hydrophone line array, The re are two major issues in this approach: one is the feasibility of ac oustic inversion with a limited aperture line array, the other is rela ted to the knowledge of the geometry of the experimental configuration . To test the feasibility of this approach, a 40-hydrophone-4-m spaced towed array together with a low-frequency acoustic source, was operat ed at a shallow water site in the Strait of Sicily, In order to estima te the array deformation in real time, it has been equipped with a set of nonacoustic positioning sensors (compasses, tilt-meters, pressure gauges). The acoustic data were inverted using two complementary appro aches: a genetic algorithm (GA) like approach and a radial basis funct ions (RBF) inversion scheme, More traditional methods, based on core s ampling, seismic survey and geophone data, together with Hamilton's re gression curves, have also been employed on the same tracks, in order to provide a ground truth reference environment, The results of the ex periment, can be summarized as follows: 1) the towed array movement is not negligible for the application considered and the use of position ing sensors are essential for a proper acoustic inversion, 2) the inve rsion with GA and RBF are in good qualitative agreement with the groun d truth model, and 3) the GA scheme tends to have better stability pro perties, On the other hand, repeated inversion of successive field mea surements requires much less computational effort with RBF.