Mid-frequency synthetic aperture sonar imaging

A detailed review of many temporal stability and spatial coherence experiments is used to develop a reasonable model for the temporal and spatial limitations on mid-frequency synthetic aperture sonar (SAS) in shallow water. A comparison of deep- versus shallow-water coherence experiments is made based on an extensive review of the literature. This comparison reveals that the spatial limits for arrays often dominate over temporal limits. The upper bounds on real or synthesized array lengths in shallow water that result from this analysis are presented. The feasibility of mid-frequency SAS imaging in shallow water is shown, and the predicted resolution in range, azimuth, and depth is compared to the theoretical values for a perfectly stable ocean and precise motion compensation. As a first step to validate the spatial and temporal limitation analysis, a mid-frequency surface sonar is modeled to create artificial data for SAS imaging in shallow water. The modeled environment includes a time varying ocean surface and sound-speed profiles, bottom roughness, penetration, and scattering. Useful SAS imaging is shown. [Work supported by NUWC.]