Impact of a shelfbreak front on array processing in shallow water

Abstract

In a coastal ocean shelfbreak front region, underwater sound can horizontally refract in the offshore direction due to the sloping bottom and reflect/refract back shoreward due to the ocean front. To study this interesting phenomenon, an analytic solution for an ideal wedge with a frontal interface was introduced in our previous paper [Lin et al., J. Acoust. Soc. Am. 120, 3182 (2006)]. This analytic solution suggests that the sound will also tend to propagate along the front, and that so-called ‘‘whispering gallery’’ modes can be observed. In this paper, the consequence of this whispering gallery effect on array processing is discussed. Specifically, the influence of an ideal ocean front on the array gains is studied. Since the sound reflecting from the ocean front forms highly correlated beams, the array gain of a horizontal hydrophone array will be increased. In addition, the application of modal beamforming techniques to resolve the whispering gallery modes propagating along the front is demonstrated. Our research goal for this study is to pursue practical systems to locate an inshore, long-distance sound source and also to monitor the changes of ocean fronts.