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Effects of naturally occurring bubbles on multibeam sonar operations

The acoustic effects of bubbles can have a major impact on hydrographic operations using multibeam sonars and on the quality of the data they produce. It is well-known that bubble sweepdown, bubbles entrained beneath the hull due to high ship speeds or heavy weather, is a significant problem, and means to mitigate the effects are sought. The bubble problem discussed in this paper has a different source - one which hydrographers have not yet taken into account. The bubbles that cause this problem are those naturally occurring in the sea. Natural bubbles exist in the ocean due to many causes such as breaking waves, rip currents carrying bubbles produced in surf zones out into deeper waters, impact of rain drops, swim bladders of sea life, and gas hydrates bubbling up from the seafloor. This paper discusses the characteristics of bubbles caused by breaking wind waves and rip currents and their effects on multibeam-sonar operations.