Propagation medium impact on sonar coherent processing for high frequency synthetic aperture imaging

The major benefit of using synthetic aperture sonar (SAS) in underwater imaging applications is the provision of near-optical quality imaging at practical area coverage rates without the need for large physical aperture sizes that carry with them impractical size, weight and power requirements for the host platform. Characterization of the underwater propagation medium´s spatio-temporal coherence limitations is a pre-requisite to an effective synthetic aperture sonar (SAS) system design. Raytheon Company, in conjunction with Harbor Branch Oceanographic Institute, has designed and successfully conducted an acoustic medium stability experiment to provide such measurements. The experiment accurately characterizes the medium´s coherence simultaneously in both space and time by employing a stationary acoustic projector and a large, stationary acoustic array that is long enough to encompass candidate SAS design lengths without requiring platform motion. The experiment is described, and the temporal coherence measurements are presented