Abstract:

Schmidt and Kuperman [J. Acoust. Soc. Am. 97, 2199--2209 (1995)] show that it is possible to treat multiple scattering in media with elastic and fluid layers separated by rough interfaces. Their work, based on a ``smoothing'' approximation, shows that the coherent (mean) field obeys certain effective boundary conditions. These boundary conditions account for some of the multiple interactions between interfaces. Kuperman and Schmidt also compute the second moment of the scattered field. However, their computations of the second moment include multiple scattering only insofar as the fields which are scattered are the mean fields which depend on the effective boundary conditions. Recent work [Sanchez-Gil et al., Phys. Rev. B 50, 15353--15368] shows that to account for enhanced backscattering from roughness overlying a waveguide structure, multiple scattering theory for the incoherent field is required, beyond the smoothing approximation. This work will examine consequences of their multiple scattering formalism for fields within a waveguide and identify the problems that make the interior problem distinct from that of determining the differential cross section, i.e., the exterior problem.