DETECTION OF A SUBMERGED OBJECT INSONIFIED BY SURFACE NOISE IN AN OCEAN WAVE-GUIDE

A theory is developed and applied to determine whether an object subme rged in an ocean waveguide and insonified only by surface-generated no ise can be detected with conventional sensing arrays. An expression fo r the total noise-field covariance of a stratified waveguide with a su bmerged object present is derived using full-field wave theory. This i s evaluated by numerical wave-number integration for a spherical objec t in a shallow water waveguide. The Cramer-Rao lower bound on detectio n error is computed for several realistic shallow water scenarios at b oth low and high frequency. The results indicate that cross-range loca lization is possible when the array aperture is sufficient to resolve the object scale. This conclusion is supported by beamforming simulati ons. Range localization is possible at greater distances. However, thi s requires high correlation between direct and scattered noise fields at the sensor, which is difficult to replicate via matched field proce ssing. In addition, wave theory indicates that high resolution imaging of reflected ambient noise is generally most effective within the dee p shadow range of the object. Beyond the deep shadow range, diffractiv e interference from the total forward field may overwhelm reflections, depending upon the incident noise directional spectrum and measuremen t range. Overall, present analysis indicates that the proposed detecti on scheme presses the limits of current technology.