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Summary

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:

Total 73 R/V stations for acoustical measurements and 9 ABS installations were done and over 400 individual transmissions from the different sources were recorded. An independent database of 157 direct CTD cast was collected to initiate the inversion and verify its results.

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.


next up previous contents
Next: References Up: INTAS Final Report Previous: Management and Financial Information

Dmitry Mikhin
Sun Dec 8 11:32:03 GMT+0300 1996