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

2pUW4. Can strong mode coupling be exploited?

B. Edward McDonald

Naval Res. Lab., Washington, DC 20375

W. A. Kuperman

Marine Phys. Lab., Scripps Inst. of Oceanogr., La Jolla, CA 92093

The Heard Island Feasibility Test brought to light higher levels of acoustic mode coupling than some researchers had expected. Mode coupling appears to complicate the interpretation of propagation experiments. Investigation is beginning into whether complexity in modal energy distribution has positive rather than negative implications for the ATOC program (acoustic thermometry of ocean climate). Mode coupling matrix elements consist of vertical integrals involving the local acoustic eigenmodes and horizontal gradients of environmental variables. The coupling matrix separates into a component due to bathymetric interaction and a component due to volumetric inhomogeneities. The different symmetries of these two components may help to identify their separate contributions to mode coupling along a specific propagation path. For strong mode coupling, the eigenstates of the coupling matrix and examined. Such eigenvalues consist of vertical mode populations (which are called ``supermodes'') in which energy circulates among the acoustic modes in fixed patterns along the propagation path. The question of what the supermodes look like, and whether they can be identified in propagation experiments will be addressed. [Work supported by NRL and ARPA.]