### ASA 126th Meeting Denver 1993 October 4-8

## 2pAO1. Long vertical arrays in acoustical sounding of the ocean.

**A. Voronovich
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*Wave Propagation Lab./NOAA/Environmental Res. Labs., Boulder, CO 80303
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Using long vertical arrays (LVAs) in ocean acoustics enables one to
measure an S matrix describing transformations of modes in inhomogeneous
waveguides. The S matrix allows one not only to calculate the sound field for
any configuration of sources and receivers but also to proceed to the solution
of the inverse problem (IP)---retrieving inhomogeneities from acoustical data.
The wave-type IP is studied for the 1-D case, which differs significantly from
the multidimensional situation. For instance, in the 2-D case, the IP can be
solved based only on the submatrix describing forward scattering as a function
of frequency. The 2-D irregularities in the acoustic waveguide could be
reconstructed as in the 1-D problem with the help of the layer-peeling
algorithm via backscattering data. But this approach is of little practical use
because backscattering is usually weak. Practical formulation of the
deterministic IP in ocean acoustics should exploit some final-dimensional
description of the media and use all available data about the S matrix. For
example, using phases of diagonal elements measured at only two close
frequencies leads to the Munk--Wunsch scheme of modal ocean tomography. In the
general case, a numerical-evolution-type algorithm is proposed to solve this
nonlinear problem in the spirit of the invariant imbedding approach. [Work
supported by NRC and PPSIO of Russia.] [sup a)]On leave from the P. P. Shirshov
Institute of Oceanology, Moscow, Russia.