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

1pAO5. Mode coupling and other effects of modeled propagation through continental-shelf internal solitary waves.

James C. Preisig

Timothy F. Duda

Appl. Ocean Phys. and Eng. Dept., Woods Hole Oceanogr. Inst., Woods Hole, MA 02543

Acoustic propagation through a continental-shelf waveguide containing internal solitary waves has been modeled with the finite-element parabolic equation (FEPE). The waveguide has two essentially mixed layers separated by a gradient layer, with a homogeneous, lossy bottom. Solitary waves (pycnocline depressions) of many sizes and shapes are included, not all of which fit the dispersion relation. Including both physical and unphysical waves aids interpretation of the forward-scattering (mode coupling) mechanism. Solitary waves of horizontal scale length 50 to 150 m cause significant mode coupling. Longer and shorter solitons give weaker coupling. For cw signals (400 Hz), the results of a sudden approximation model for a single soliton are compared to those generated with the FEPE model and provide some insight into the mode coupling behavior. The results for a broadband pulse (e.g.,400- to 525-Hz band) show a first-order difference in waveform shape after propagation through a soliton when compared to the result with no soliton. This leads to the conclusion that received signal predictability based upon perturbation of layered-only propagation is problematic in the presence of the waves. [Work supported by ONR.]