The following section describes the model for scattering from and out of the bottom with sand ripples. This work is based on the second order perturbation theory 1 of scattering from sand ripples. It assumes that the scattering into the sediment is approximately described by Snell's law for angles above the critical angle, and by second order perturbation theory below the critical angle. This section ignores the effects of small-scale roughness and volume inhomogeneities. Abstract PC SWAT

more »

... nal Computer Shallow Water Acoustic Tool-set) is a sonar simulation package developed at Coastal Systems Station to predict acoustic sensor performance. This article focuses on the algorithms used by PC SWAT to generate synthetic images of proud, buried, and partially buried three-dimensional targets. High frequency scattering from the target is described by a combination of the Kirchhoff approximation and the Geometric Theory of Diffraction. Propagation of sound into a marine sediment with ripples is described by an application of Snell's law and second order perturbation theory in terms of Bragg scattering. Let i ϑ be the grazing angle of the incident field, and ϕ be the azimuthal angle between the incident field and the direction of the ripple field. Neglecting small-scale roughness, the scattering into the sediment is composed of five terms. The first is the coherent component due to Snell's law. The remaining components are the lowest order terms for Bragg diffraction of sound into the sediment by the ripple structure. It is these last remaining terms that play the dominant role of scattering into the sediment for sub-critical grazing angles. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF PAGES 7 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18