Cable strum self-noise cancellation for sonar towed arrays

Abstract

Nonacoustic self-noise observed on marine seismic streamers and towed sonar arrays represents a serious problem for acoustic source detection at low frequency. Towed array self-noise, also known as cable strum, consists of mechanical vibrations induced by vortex shedding. Transverse vibrations in the array body subject each hydrophone pressure head to local accelerations. The resultant acoustic response can be several orders of magnitude stronger than the water-borne acoustic signals of interest. In this paper, a beamspace, time-domain adaptive signal processing architecture for the coherent rejection of broadband nonacoustic self-noise is presented. The approach is based on the recognition that most vibrational modes of a towed array propagate at phase speeds substantially less than those of acoustic signals in the water column. This property supports the formation of a signal-free, strum reference using the same sensor that samples the acoustic data. The approach removes the need for additional measurement channels, such as accelerometers or strain gauges, to independently sense the undesirable distortions introduced by cable strumming. The phenomenology underlying flow-induced self-noise for towed arrays is discussed and characterized using k-w analysis. An overview of the method is presented and cancellation performance is demonstrated using snapshots of passive sonar towed array data. [Work sponsored by the Department of the Navy, under Air Force Contract F19628-95-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the U.S. Air Force.]