Abstract: A system and method of indirect underwater acoustic ocean surveillance is sclosed requiring at least two sonar platforms, usually ships, travelling some distance apart. At least one of the platforms transmits sonar pulses, portions of which are scattered off the ocean floor to at least one companion sonar receiver platform. The receiver platform is provided with means to analyze the received scattered sonic pulses to determine if a submerged object such as a submarine is obstructing a portion of the pulse, thus casting an acoustic shadow. With accurate positioning information supplied by a navigation information system such as the NAVSTAR GLOBAL POSITIONING SYSTEM (GPS), and by combining pulse measurements over several positions the system will be able to locate, identify, and track the obstructing object by analyzing these acoustic shadows or silhouettes. Geometric silhouette reconstruction techniques and other mathematical techniques may be employed to construct an image of the submerged object.

Abstract: A bistatic system and method is disclosed for mapping a large swath of the ocean bottom on a single sweep using two survey ships traveling approximately side-by-side some distance apart on parallel courses. Each ship transmits a fan shaped sonic pulse or ping symmetrically downward about the vertical and transverse to the ship's longitudinal axis and processes the backscattered echo for depth. The forward scattered portion of this pulse or a second sonic pulse transmitted downward at an angle between the ships toward the other ship is received by the other ship and is analyzed to determine ocean bottom depths of the swath between the ships. The analyzed width of an insonified swath portion is sufficiently wide so as to overlap, at an edge, with an edge of each adjacent insonified swath portion analyzed. This partial redundancy provides a means for continuous calibration by comparing depth determinations for consistency and accuracy.