Soundscapes and ambient noise in the ocean

摘要

Ambient noise in the ocean has been studied for around 80 years and many hundreds of papers have been published. It is called noise in the context of the operation of sonar, since it is the main noise against which sonar signals must be detected, even though it has included many studies from mechanisms of sound generation to the use of sound by marine animals. Generally ambient noise refers to the background noise from all sources, excluding sounds from individual identifiable sources. Recently, there has been increasing reference to soundscapes for what appears to be much the same phenomenon. This has coincided with the development of interest by biologists in ambient noise, mainly in the context of the effects of noise on marine animals and their use of sound. Is soundscape simply a trendy new name for ambient noise or is it something different? Judging by what has been published on ocean soundscapes, it seems to be little more than a trendy new name. However, the term soundscapes has been widely used for much longer in many diverse applications from music, to architecture to terrestrial ecology and covers more than just ambient noise. This paper examines the wider use of the term soundscapes in other applications. It considers how these compare with ambient noise in the ocean and how ocean soundscapes might be defined to be more than simply a trendy name for ambient noise as well as being consistent with usage in other areas. The concept of ambient noise as the background noise against which signals of interest must be detected means that ambient noise is both unwanted sound and a necessary component of the sonar equation. This applies equally to our sonars and to the use of sound by marine animals. Soundscape is a broader concept, including all sounds of the environment, including not just the ambient noise but also signals of individual sources, whether the signals of interest to the sonar operator or to a marine animal, or signals that interfere with the capability of the sonar or the animal to make use of sound. For the ocean context, probably the most useful analogy is with soundscapes in terrestrial ecology.