Gregory J. Orris
Michael D. Collins
U.S. Naval Res. Lab., Washington, DC 20375
Scripps Inst. of Oceanogr., Univ. of California, San Diego, La Jolla, CA 92093
Michael B. Porter
New Jersey Inst. of Technol., University Heights, Newark, NJ 07102
A three-dimensional propagation model is presented that takes into account the elastic properties of the ocean bottom and is applicable to problems of long range and low frequencies. This method allows global-scale calculations appropriate for ocean monitoring programs to be performed with environments for which solution techniques have been heretofore unavailable. The model is an extension of the adiabatic parabolic-equation method, which uses the normal-mode solutions in the waveguide for the depth dependence of the acoustic field. A modified two-dimensional parabolic equation model is used to determine the range and azimuth dependence of the acoustic field, thus providing a three-dimensional solution. It is shown that the inclusion of elastic material, with both compressional and shear waves, in bathymetric features causes larger loss and larger shadow zones behind sea mounts and islands due to the effective softening of the material. The method is compared with exact solutions and experimental results and is found to be in excellent agreement for regimes for which the adiabatic approximation is valid (i.e., for regions of slowly varying bathymetry and sound-speed profiles).