Mitigation of low-frequency underwater anthropogenic noise using stationary encapsulated gas bubbles

Abstract

Collections of bubbles cause significant dispersion and attenuation of underwater sound near the individual bubbles' resonance frequencies and can potentially be used to abate low-frequency anthropogenic underwater noise. Such effects have been reported for large encapsulated bubbles with resonance frequencies below 100 Hz [J. Acoust. Soc. Am. {\bf{127}}:2015 (2010)] and significant attenuation due to bubble resonance phenomena and acoustic impedance mismatching was observed in experiments using a compact electromechanical acoustic source [J. Acoust. Soc. Am. {\bf{128}}:2279 (2010); J. Acoust. Soc. Am. {\bf{129}}:2462 (2011)]. We describe a method of shielding either a noise source or a receiver using screens or curtains of large encapsulated bubbles. This method was applied to two distinct types of real-world noise excitation: continuous wave noise radiated by a vibrating marine vessel and impact noise from marine pile driving. Experimental results show significant noise reduction ranging up to 40 dB can be attained using this method. In addition, a model of encapsulated bubble dynamics was developed and has been used in conjunction with numerical models to design the encapsulated bubble curtain systems. [Work supported by Shell Global Solutions and the ARL:UT IR&D Program.]