Scattering resonances, filtering with reversible SAS processing, and applications of quantitative ray theory

Features present in synthetic aperture sonar (SAS) images associated with elasticity and the structural resonances of viewed objects are sometimes neglected when using SAS data for classification purposes. Other ways of processing sonar data sometimes emphasize the frequency response of the viewed object. The research described here concerns a hybrid approach based on a reversible SAS algorithm in which the acoustic spectral content contributing to a specified region of the SAS image can be extracted. The SAS algorithm uses deconvolution. An example from a small scale tank experiment using a transducer scanned along a line illustrates some applications of the method in which quantitative ray theory is useful for interpreting the image and spectral features. The method is also proved to be useful for investigating spectral responses of several objects placed proud on sand viewed simultaneously in SAS scans in a fresh water pond. The hybrid processing technique simplifies the acquisition of spectral data by reducing the spectral contamination from adjacent sufficiently separated objects.