Generation of Synthetic SAS Data for Targets Near the Seafloor: Propagation Component

Abstract

Abstract : Monostatic synthetic aperture sonar (SAS) data sets for the scattering from a target in a waveguide can be simulated via a fast model that combines an acoustic ray approximation for propagation in the waveguide with far-field scattering from a target in free-space. With the assumption that acoustic rays arise from the source and receiver and their images, the problem of wave propagation and scattering from a target within the waveguide is replaced by a superposition of a set of free-field scattering problems. Under normal operating conditions, the separation distance between a SAS platform and a target is large compared to the carrier wavelength of the transmitted signal, and hence, the free-field scattered signal can be reduced to a far-field approximation where a spherically diverging wave is weighted by a scattering amplitude. The scattering amplitude contains all of the information about the scatterer (e.g., its material properties) and the directionality of the scattered field. A scattering amplitude can be obtained from a direct measurement or a finite-element analysis of a target. The fast ray model allows one, who is interested in SAS processing algorithms, to generate data sets with variations in the environment or source-receiver-target geometry without incurring the expense associated with the collection of actual SAS data. Results from the fast ray model will be compared to data and finite-element results for several targets in shallow water. The horizontal range to the targets and time gating permit the air-water interface to be ignored.