Brian H. Tracey
Henrik Schmidt
Dept. of Ocean Eng., MIT, 77 Massachusetts Ave., Bldg. 5-007, Cambridge, MA 02139
In shallow-water environments scattering from rough surfaces and volume inhomogeneities acts to degrade sonar performance. An efficient normal mode method has been developed to model the resulting reverberation. The self-consistent perturbation theory of Schmidt and Kuperman [J. Acoust. Soc. Am. 97, 2199--2210 (1995)] has been reformulated in terms of normal modes to handle scattering from rough fluid and elastic interfaces. A similar, recently developed volume scattering theory is used to model the effects of sound speed and density fluctuations in the seabed and water column. The two theories are integrated numerically and used to contrast the different scattering mechanisms. Waveguide propagation effects are seen to be extremely important. Spatial correlation and modal cross-correlation statistics are estimated and used to study decorrelation of the sound field. Excellent agreement with the wave-number integration implementation by Schmidt and Kuperman is demonstrated for the case of rough interface scattering, with the modal approach requiring significantly less computation for low-frequency shallow-water scenarios.