### ASA 127th Meeting M.I.T. 1994 June 6-10

## 3aUW11. Range variation in a numerical average underwater acoustic
propagation method.

**Roger M. Oba
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*Naval Res. Lab., Stennis Space Center, MS 39529-5004
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A computational method of numerically computing average complex pressure
field has been developed using a normal mode analysis of the forward
propagating solutions of the Helmholtz equation [R. M. Oba, Acoust. Lett. 16,
56--61 (1992)]. It computes the transmission loss and phase for the average
solutions in the continuous wave case in piecewise range-independent cases as
well as a case of rapid fluctuations in range. Suppose the uncertainty can be
probabilistically modeled within range intervals as ensembles of sound speeds.
If for each sound speed in the ensemble the variation within each interval is
relatively small, and if the variations within the ensemble are uniform, then
modification of the existing method allows computation of average volumetric
forward and backward propagation. This technique will be useful in matching
this computed average field at some final range to a deterministic solution
starting from that range on. This technique can also be used in the limit of
small intervals of uncertainty. [Work supported by Naval Research Laboratory
and the Office of Naval Research.]