Anthropogenic and natural sources of ambient noise in the ocean
Anthropogenic and natural sources of ambient noise in the ocean
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DOI：
10.3354/meps08353
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发表时间：
2009-01-01
影响因子：
2.5
通讯作者：
Hildebrand, John A.
中科院分区：
文献类型：
--
作者：
Hildebrand, John A.
海洋环境噪声有人为和自然两种来源。不同的噪声源在三个频带中占主导地位：低（10至500赫兹），中（500赫兹至25千赫）和高（>25千赫）。低频波段主要是人为来源：主要是商业航运，其次是地震勘探。由于低频声音几乎没有衰减，从而允许远距离传播，因此航运和地震源会造成海洋盆地的环境噪声。在过去的几十年里，航运对环境噪声的贡献增加了多达12分贝，与此同时，世界商业航运船队的船只数量和规模也在显著增加。在此期间，沿大陆边缘的石油勘探和建设活动已经进入更深的水域，地震信号的远程传播也增加了。中频声音由于衰减更大，不能长距离传播，只有本地或区域（10公里远）的声源才会产生环境噪声场。中频波段的环境噪声主要是由海面搅动引起的：破碎的海浪、浪花、气泡的形成和崩塌以及降雨。各种声纳（例如军用声纳和测绘声纳）以及小型船只都会在中频产生人为噪声。在高频时，声衰减变得极端，所有噪声源都被限制在靠近接收器的区域内。热噪声是水听器附近水分子布朗运动的结果，是约60 kHz以上的主要噪声源。
Ocean ambient noise results from both anthropogenic and natural sources. Different noise sources are dominant in each of 3 frequency bands: low (10 to 500 Hz), medium (500 Hz to 25 kHz) and high (>25 kHz). The low-frequency band is dominated by anthropogenic sources: primarily, commercial shipping and, secondarily, seismic exploration. Shipping and seismic sources contribute to ambient noise across ocean basins, since low-frequency sound experiences little attenuation, allowing for long-range propagation. Over the past few decades the shipping contribution to ambient noise has increased by as much as 12 dB, coincident with a significant increase in the number and size of vessels comprising the world's commercial shipping fleet. During this time, oil exploration and construction activities along continental margins have moved into deeper water, and the long-range propagation of seismic signals has increased. Medium frequency sound cannot propagate over long ranges, owing to greater attenuation, and only local or regional (10s of km distant) sound sources contribute to the ambient noise field. Ambient noise in the mid-frequency band is primarily due to sea-surface agitation: breaking waves, spray, bubble formation and collapse, and rainfall. Various sonars (e.g. military and mapping), as well as small vessels, contribute anthropogenic noise at mid-frequencies. At high frequencies, acoustic attenuation becomes extreme so that all noise sources are confined to an area close to the receiver. Thermal noise, the result of Brownian motion of water molecules near the hydrophone, is the dominant noise source above about 60 kHz.