Acoustic tomography in the Western Mediterranean from a moving ship

A moving ship tomography experiment was carried out in the Western Mediterranean in 1994. Broadband sound signals were emitted by six moored transceivers deployed by IfM (Kiel, Germany), IFREMER (Brest, France), and WHOI (Woods Hole, USA), in the framework of the THETIS–2 project and recorded at a hydrophone deployed from a drifting research vessel. The acoustic measurements were supplemented with a detailed CTD survey. The data processing technique used made it possible to compensate for the Doppler shift due to vessel drift, measure the channel pulse response and estimate the arrival angles of different rays. The arrival pattern proved to be consistent with numerical predictions using adiabatic normal modes and ray theory. The first results of tomographic inversion for a single vertical slice are presented. The travel times of early raylike arrivals and final cutoffs constitute the data set for inversion. For distances over 300 km, late modal arrivals were resolved, identified and incorporated into the data set. An alternative inversion approach based on matching the overall arrival pattern is discussed and compared with traditional schemes. [Work supported by ISF, INTAS, and RBRF.] a)On leave from P. P. Shirshov Oceanography Institute, Moscow, Russia.