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

J. B. Bowlin

Woods Hole Oceanogr. Inst., Bigelow 2, Woods Hole, MA 02543

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.