Comparison Between Three Approaches to the Ocean Acoustic
Tomography: Field Experiment and Numerical Simulations
INTAS-93-0557 -- May 1995 - July 1996
Michael Taroudakis, Project Co-ordinator
The project is aimed at creation of experimental database for adequate comparison of three approaches to the ocean acoustic tomography: conventional technique with moored transceivers, Moving Ship Tomography (MOST), when the signals are emitted or recorded by a mobile R/V surveying the area under study, and Matched Field Tomography with long vertical arrays. Seven transceivers were moored in the Western Mediterranean basin in early 1994 in the framework of the THETIS-2 project, carried out in conventional technique by IfM (Kiel, Germany), IFREMER (Brest, France) and WHOI (Woods Hole, U.S.A.). These transceivers also served as broad-band sound sources for MOST and Matched Field tomography experiments. During the field expedition on-board the R/V ``Akademik Sergey Vavilov'' of the Russian Academy of Sciences four tomographic surveys of the basin were completed:
A special data-processing technique was developed for precise compensation of the Doppler effect due to R/V drift, estimated with 0.5-1.0 cm/s accuracy. In more than 80% of receptions the processing revealed stable arrival patterns with good SNR and multiple resolvable ray (at distances over 300 km also modal) arrivals up to 400-600 km range for different sources. An innovative inversion approach based on matching the overall arrival pattern is proposed and compared with traditional linear scheme. Tomographic inversion is done for 2 sections in the northern and southern parts of the basin. The reconstructed 2D sound speed fields in these vertical slices proved to be in good agreement with independent oceanographic measurements. Comparison of inversion results for June and July parts of the MOST experiment demonstrated the temporal changes of the medium were successfully measured in moving ship approach.