Abstract:

Noise sources and noise reduction techniques in cable suspended SONAR systems (i.e., sonobuoys) are discussed. The sonobuoy has evolved from a hydrophone on a simple cable to a sophisticated suspension system as a result of the requirement to provide acoustic performance over extended bands of the acoustic spectrum in the hostile ocean environment. An overview of the progressive identification and solution of self-noise problems in sonobuoys illustrates the layered nature of noise sources. Sonobuoy self-noise specifications evolved from those of traditional audio systems to the specification of hydromechanical performance requirements to limit vibration-induced self noise. The specification of self-noise performance further evolved to produce specifications that relate flow- and vibration-induced self noise directly to the sonobuoy acoustic performance. Examples of noise attenuation, energy decorrelation, and translation of noise energy out of the band of interest are presented. The possible mechanisms of wave- and flow-induced hydrophone noise are discussed, including the concept of vibration-induced head changes as a source of self noise on acoustic pressure hydrophones. A brief review of the progress in the reduction of flow noise on gradient hydrophones is included.