MODELING SEA-FLOOR GEOACOUSTIC INTERACTION WITH A NUMERICAL SCATTERING CHAMBER

A numerical scattering chamber (NSC) has been developed to compute bac kscatter functions for geologically realistic seafloor models. In the NSC, solutions are computed to the elastic (or anelastic) wave equatio n by the finite-difference method. This has the following advantages: (a) it includes all rigidity effects in the bottom including body and interface waves. (b) It can be applied to pulse beams at low grazing a ngles. (c) Both forward scatter and backscatter are included. (d) Mult iple interactions between scatterers are included. (e) Arbitrary, rang e-dependent topography and volume heterogeneity can be treated simulta neously. (f) Problems are scaled to wavelengths and periods so that th e results are applicable to a wide range of frequencies. (g) The metho d considers scattering from structures with length scales on the order of acoustic wavelengths. The process is discussed for two examples: a single facet on a flat, homogeneous seafloor and a canonically rough, homogeneous seafloor. Representing the backscattered field by a singl e, angle-dependent coefficient is an oversimplification. In a strong s cattering environment, time spread of the field is a significant issue and an angle-dependent separation of the wave field may not be valid.