### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 3aAO2. Nonlinear tomographic inversion by using the WKB modal condition.

**E. C. Shang
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Y. Y. Wang
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A. G. Voronovich
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*CIRES, Univ. of Colorado/NOAA/ETL, Boulder, CO 80303
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In the HRT (horizontal refraction tomography) scheme [A. G. Voronovich and
E. C. Shang, J. Acoust. Soc. Am. 95, 2851(A) (1994)], the 3-D tomographic
inversion is performed in two stages: (1) retrieving the modal wave numbers
k[inf m](x,y) in the horizontal plane and (2) reconstructing the sound-speed
profile SSP in the vertical at each node of the horizontal plane basing on a set
of retrieved modal wave numbers k[inf m](x,y). Usually, a nonlinear approach has
to be considered for the 1-D vertical inversion of the second stage. In this
paper, the nonlinear inversion by using the WKB modal condition is proposed. The
advantages of using WKB modal condition are: (a) it is efficient, the data k[inf
m](x,y) can be matched directly to SSP without a model-based calculation
(replica); (b) it works even if just a few modes are available; and (c) the
error can be analyzed. Some results of numerical simulation are discussed. [Work
supported by ONR.]