Holographic and conventional bistatic synthetic aperture sonar imaging of cylinders: Comparison and ray interpretation

Abstract

When synthetic aperture sonar is used to image elastic targets, subtle features can be present in the images associated with the dynamical response of the target being viewed. In an effort to improve the understanding of such responses as well as to explore alternative image processing methods, a laboratory-based system was developed in which targets were illuminated by a transient acoustic source and bistatic responses were recorded by scanning a hydrophone along a horizontal line. Images were constructed using a relatively conventional bistatic SAS algorithm and were compared with images based on supersonic holography. The holographic method is a simplification of one previously used to view the time evolution of a target’s response [B. T. Hefner and P. L. Marston, ‘‘Acoustics Research Letters Online’’ 2, 55–60 (2001)]. In the holographic method, the time evolution of the cross-range image was used to construct a two-dimensional image with an effective range coordinate. Various features for cylindrical targets were interpreted using quantitative ray theory. This includes contributions from guided surface elastic waves as well as transmitted-wave features. [Work supported by the Office of Naval Research.]