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

## 3aUW9. Caustic formation and timing changes in long-range propagation from
ocean sound-speed relative curvature.

**T. F. Duda
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J. B. Bowlin
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*Woods Hole Oceanogr. Inst., Bigelow 2, Woods Hole, MA 02543
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A depth-dependent parameter of ocean sound channels has been found, using
numerical simulation, to strongly influence long-range deep-ocean geometrical
ray propagation. This parameter, representing sound-speed relative curvature,
is the second vertical derivative of sound speed divided by the square of the
first derivative. Ray and wave front timing and intensity can be influenced
within realistic ocean sound channels by unpredictable wave front triplications
and caustics associated with high values of the parameter at ray turning
points. The relative curvature behaves as a random variable because of ocean
finestructure, causing unpredictability. The parameter has a higher rms value
near the sound-speed minimum for both an internal-wave model and actual data.
This effect is a plausible explanation of poor multipath resolution and
identifiability late in 250 Hz (center frequency) pulse trains transmitted 1000
km in the North Pacific.