海面波浪谱对深海低频环境噪声的影响

提出了一种适用于深海低频环境噪声的波浪谱,通过声压谱和波浪谱的理论关系,分析了深海低频噪声在百赫兹以下的谱特征,解释了不同频段噪声谱的主要产生机理。将深海传播条件下海面波浪谱与海面风速相结合,利用波浪发声理论得到一种低频海洋环境噪声理论表示方法。仿真结果表明,波浪谱决定着辐射噪声谱的强度和斜率,本模型得到的理论噪声谱可以对低频海洋环境噪声进行预报。2016年的深海实验观测数据分析显示,统计的环境噪声谱级在1 Hz至100 Hz频段范围内大于70 dB,并且噪声谱在低频段呈倒“N”型,在3⁴ Hz处为噪声谱的谷值,噪声级为70 dB,在50 Hz处为噪声谱的峰值,噪声级为92 dB,通过理论计算和实验对比,相关系数为0.95,理论结果和实验测量对比结果符合较好。     

Low frequency deep ocean ambient noise trend in the Northeast Pacific Ocean

Concern about effects of anthropogenic noise on marine life has stimulated new studies to establish present-day ocean noise levels and compare them to noise levels from previous times. This paper reports on the trend in low-frequency (10-400 Hz) ambient noise levels and presents measurements made using a calibrated multi-element volume array at deep ocean sites in the Northeast Pacific from 1978 to 1986. The experiments provided spectral noise levels as well as horizontal and vertical noise directionality. The data presented here provide evidence that the trend derived from 1960s data extended to around 1980, but has since continued at a lower rate.     

海面波浪对海洋环境噪声垂直空间相关性的影响

研究了由海浪谱导得的噪声源的相关函数对海洋环境噪声垂直空间相关性的影响。常用的海洋环境噪声空间相关性模型一般假设海面噪声源是非相关的,这种假设可以解释一些物理现象,但是与真实情况并不符合。考虑到风成噪声与海浪运动的相关性,引入海浪谱,得到噪声源的相关函数,利用Kuperman-Ingenito (K/I)噪声模型,计算海洋环境噪声的垂直相关性。通过仿真结果与实验数据对比可以看出,在高风速下,假设噪声源不相关时计算得到的噪声场垂直相关性与实验结果相差较大,而利用由海浪谱导得的噪声源的相关函数计算得到的噪声场的垂直相关性与实验结果符合较好。     

The effect of ocean wave on the vertical spatial correlation of ocean ambient noise

The effect of the correlation function of noise sources derived from the ocean wave spectrum on the vertical spatial correlation of ocean ambient noise is investigated. The spatial correlation models of ocean ambient noise usually assume that the surface noise sources are uncorrelated. This assumption can be used to explain some physical phenomena, but it is not consistent with the real situation. Considering the relation between the ocean wave motion and the ambient noise generated by wind, the spectrum of ocean wave is introduced to calculate the vertical correlation of ocean ambient noise as the correlation function of noise sources by using the Kuperman-Ingenito(K/I) noise model. The comparison of the simulations and the experimental data shows that the simulations of vertical correlation of ambient noise have some differences with the experimental data by assuming the noise sources are uncorrelated and the simulations of vertical correlation of ambient noise have a good agreement with the experimental data by using the correlation function of noise sources derived from the ocean wave spectrum under the situation of high wind speed.     

海洋环境噪声反演估计海面风速

海洋环境噪声与海面风速高度相关。本文在研究国内近年来测量数据的基础上,给出环境噪声级与风速的关系。提出按风速分段(三段)线性拟合环境噪声与对数风速关系曲线的方法,提出并确定最佳反演频段。在麦岛海域,由实测数据确定了分段拟合参数,获得在 0.1~ 22.6 m/s的风速范围内,由海洋环境噪声估计海面风速的误差在 10%以下的优良结果。     

Estimation and interpolation of underwater low frequency ambient noise spectrum using artificial neural networks

In this work, estimation of ambient noise spectrum influenced by wind speed and wave height carried out for the frequency range of 500 Hz to 5 kHz using Feed forward Neural Network (FNN) is presented. Ocean ambient noise measurements were made in the shallow waters of Bay of Bengal using a portable data acquisition system with a high sensitivity hydrophone at a depth of 5 m from the surface.100 sets of data covering a rage of wind speeds from 2.5 m/s to 8.5 m/s with approximately 15 sets of data falling within 1 m/s over the range of wind speed were used for training the FNN. The parameter wave height which contributes to the noise producing mechanism is also used for training along with wind speed. The results revealed that the proposed method is useful in the estimation and interpolation of underwater noise spectrum level and hence in simulation for the considered frequency range. These were confirmed by calculating the Mean Squared Error (MSE) between the experimental data and the simulation. As the measurements of the underwater ambient noise level are very difficult in remote oceanic regions, where conditions are often inhospitable, these studies seem to be relevant.     

Estimating the sound speed of the surface layer of the seabed using ocean ambient noise in shallow water

To improve the inversion efficiency, a method for quickly and directly estimating the sound speed of the surface layer of the seabed is proposed. According to the energy flux theory, the ocean ambient noise data received by the vertical line array can be used to extract the bottom loss(BL) passively. The BL curve has an effect on the critical angle, which is used to estimate the sound speed of the surface layer of the seabed. Based on the ray model,the difference between the BL calculated from t...     

Analysis on spatial difference of ocean ambient noise spectrum in the northern South China Sea

To study the spatial difference of ocean ambient noise in offshore China and reveal its generation mechanism, the difference between the noise level(NL) of two stations is compared based on long-term observation data collected in the same season. Considering the influence of underwater acoustic channels and the characteristics of noise sources, the transmission loss level(TL) from the port ship noise sources to the measuring station is analyzed and it shows a strong correlation between the transmission loss difference(TLD) and noise level difference(NLD) at the band of 50-500 Hz. At the same time, the analysis of ship noise source level(SL) presents a difference about 20 dB between the two ports, corresponding to the variation of the ship density before and during the fishing moratorium. The results prove that the ambient noise is closely related to ship noise sources at this frequency band, and the noise difference between the two stations results from the transmission loss and the ship noise sources.     

南海北部海洋环境噪声谱级空间差异性分析

为研究中国近海海洋环境噪声的空间差异性,揭示其形成原因,以同一海域同一季节两个测量站位的长期观测数据为研究对象,对比两个站位噪声谱级的差异.结合海洋信道和噪声源特性的影响,分析港口强噪声源到噪声采集站位的传播损失,发现在50~500 Hz频段传播损失差值和噪声谱级差值呈现较强相关性;对港口航船噪声源级的分析发现,该频段内源级相差20 dB左右,与休渔期前后航船密度差异相对应。试验分析和研究结果表明,南海北部海域50~500 Hz频段内海洋环境噪声与航船噪声源密切相关,两站位噪声空间差异由海区传播条件差异与航船噪声源级差异共同引起。     

Estimating the sound speed of the surface layer of the seabed using ocean ambient noise in shallow water

To improve the inversion efficiency, a method for quickly and directly estimating the sound speed of the surface layer of the seabed is proposed. According to the energy flux theory, the ocean ambient noise data received by the vertical line array can be used to extract the bottom loss(BL) passively. The BL curve has an effect on the critical angle, which is used to estimate the sound speed of the surface layer of the seabed. Based on the ray model,the difference between the BL calculated from the noise extraction and the theoretical value is derived, while the beamforming performances of the array at different angles and frequencies is discussed. Considering that the sound ray bends in the environment with a non-constant sound-speed gradient, the angle needs to be corrected to improve the universality of the method.Different critical angles of different frequencies correspond to different effective depths. Data processing result of an experiment conducted in the Yellow Sea shows that within the effective depth where the critical angle remains unchanged, the surface layer of the seabed can be regarded as a constant speed layer. The sound speed of the surface layer of the seabed in this sea area is estimated at 1547 m/s within 0.5 m, which is similar to the active inversion result.     

利用海洋环境噪声估计浅海海底表层声速

为提高反演效率,提出一种快速估计浅海海底表层声速的方法。根据噪声能流理论,垂直阵接收的海洋环境噪声数据能够用于无源提取海底反射损失,反射损失曲线中具有明显的临界角效应,从而接估计海底表层声速。以射线模型为基础,推导了噪声提取的反射损失与理论值之间的差异,并讨论实际阵列波束形成在不同角度和频率下的性能。考虑到非等声速环境下声线会发生弯曲,需对角度进行修正以提高方法的广泛适用性。不同频率的临界角与有效深度之间存在对应关系,黄海某海区数据处理结果表明,在临界角不变的有效深度内,海底表层可以视为等声速层,该海区海底表层0.5 m内声速估计结果为1547 m/s,与有源反演结果相近。     

Effects of typhoon "KAI-TAK" on deep ocean ambient noise in the South China Sea

By investigating the effects on deep ocean ambient noise of typhoon "KAI-TAK" which passed the north area of the South China Sea,it is shown that the wind speed,the rainfall intensity and the long wave swell caused by typhoon affect the ocean ambient noise significantly.The correlation between the ocean ambient noise and the wind speed during the typhoon is much better than that in the non-typhoon period in the same Beaufort scale.Analysis of the correlation between the 415 h ocean ambient noise measured data and wind speed shows that,when the frequency is greater than 300 Hz,the correlation coefficient between the ocean ambient noise and the wind speed is greater than 0.5,achieving a moderate correlation;when the frequency is greater than 630 Hz,the correlation coefficient is between 0.8 and 0.9,achieving a high degree of correlation.The correlation between the ocean ambient noise and the wind speed is better than that between the ocean ambient noise and the significant wave height when the frequency is greater than 300 Hz.The correlation between the ocean ambient noise and the wind speed in infrasonic band from 10 Hz to 20 Hz is poor in the South China Sea,because the shipping is busy in this sea area and the ocean ambient noise is contaminated by the ship noise even during the typhoon.     

台风“启德”对南海深海海洋环境噪声特性的影响研究

研究台风“启德”经过南海北部对南海深海海洋环境噪声的影响,表明台风导致的风速增减、降雨强弱以及形成的长波涌浪均会影响海洋环境噪声级的大小变化,海洋环境噪声显著受到台风的影响。相同风级下,台风期间海洋环境噪声级与风速的相关性明显好于非台风期间。分析测量的415 h海洋环境噪声数据与风速、波高的相关性,频率大于300 Hz时,海洋环境噪声级与风速的互相关系数大于0.5,达到中度相关;频率大于630 Hz时,互相关系数介于0.8和0.9之间,达到高度相关;频率大于300 Hz时,海洋环境噪声级与风速的相关性好于海洋环境噪声级与波高的相关性。南海海洋环境噪声10~20 Hz的次声频与风速的相关性差,是因为南海航运繁忙,该频段的海洋环境噪声会受到航船噪声的影响,即使台风期间也不例外。      

Cross-correlation in band-limited ocean ambient noise fields

Observations of ambient noise in the ocean are generally band limited, because of the natural spectral shape of the noise or the restricted bandwidth of the detection system. Either way, the noise may be regarded as white noise to which a band-limiting filter has been applied. An analysis of the two-point cross-correlation function of such filtered noise is presented for two cases, isotropic and surface-generated noise. The most pronounced effects occur with high-pass and bandpass filters when the low-frequency cut-off falls well above the first few zeros in the coherence function. In this situation, the sensor separation is very many times the longest acoustic wavelength (associated with the lowest frequency) in the passband. The filtering then produces sharp pulses at correlation delays equal to the numerical value of the acoustic travel time between the sensors. Although these pulses are narrow, they have a finite width, within which a fine structure appears in the form of multiple rapid oscillations, due to the differentiating action of the filter. The number of such oscillations increases as the low-frequency roll-off of the filter becomes steeper. This fine structure is evident in several recently published experimental determinations of the cross-correlation function of band-limited ocean ambient noise.     

The effects of low frequency noise on people—A review

During the fast few years, the existence of high levels of man-made low frequency noise (0–100 Hz), and in particular infrasonic noise, has been reported in many environments. An effort has been made over the last decade to discover whether such high levels of low frequency noise are significant. A review of the effects of low frequency noise indicates that the effects are similar to those of higher frequency noise, that noise in the 20–100 Hz range is much more significant than infrasound at similar sound pressure levels and that the possible danger due to infrasound has been much over-rated.     

表面声道对深海风成噪声垂直空间特性的影响规律

水下风成噪声的垂直空间特性包括噪声垂直方向性和垂直相关性,研究海洋环境对其影响规律对提升声呐性能、增加海洋环境参数反演的准确性具有重要意义.本文利用Pekeris割线下的简正波理论描述噪声的传播过程,研究了深海环境下存在表面声道时,表面声道以下噪声垂直空间特性的变化规律及其原因.研究表明,在临界深度以上,表面声道的存在导致噪声垂直方向性在水平凹槽边缘靠近海底方向上的峰值升高,噪声垂直相关性随垂直距离增加先后周期地向正相干和负相干方向偏移;在临界深度以下,表面声道的存在导致水平方向上的噪声能量增强,噪声垂直相关性整体向正相干方向偏移.当表面声道的参数变化时,表面声道的厚度变化对噪声垂直空间特性影响较大,而表面声道内的声速梯度变化对噪声垂直空间特性几乎没有影响.结合各类简正波的变化分析表明,存在表面声道时,噪声源激发的折射简正波阶数增加,强度增强,是表面声道引起噪声垂直空间特性变化的主要原因.     

Increases in deep ocean ambient noise in the Northeast Pacific west of San Nicolas Island, California

Recent measurement at a previously studied location illustrates the magnitude of increases in ocean ambient noise in the Northeast Pacific over the past four decades. Continuous measurements west of San Nicolas Island, California, over 138 days, spanning 2003-2004 are compared to measurements made during the 1960s at the same site. Ambient noise levels at 30-50 Hz were 10-12 dB higher (95% CI = 2.6 dB) in 2003-2004 than in 1964-1966, suggesting an average noise increase rate of 2.5-3 dB per decade. Above 50 Hz the noise level differences between recording periods gradually diminished to only 1-3 dB at 100-300 Hz. Above 300 Hz the 1964-1966 ambient noise levels were higher than in 2003-2004, owing to a diel component which was absent in the more recent data. Low frequency (10-50 Hz) ocean ambient noise levels are closely related to shipping vessel traffic. The number of commercial vessels plying the world's oceans approximately doubled between 1965 and 2003 and the gross tonnage quadrupled, with a corresponding increase in horsepower. Increases in commercial shipping are believed to account for the observed low-frequency ambient noise increase.     

The influence of random drift of resonance-scattering harmonics on the frequency spectrum of surface acoustic reverberation in the ocean

We propose a modified model for the frequency spectrum of surface reverberation with allowance for random drift of Bragg resonance harmonics due to long wind-generated waves. The dependence of this effect on the parameters of large-scale surface waves is analyzed. Analytical expressions for the reverberation frequency spectrum are obtained for both narrow-band and wideband sounding signals. It is shown that for matched filtering of wideband signals, the considered effect leads to an increase in the effective pulse reverberation volume. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 20–30, January 2007.     

海洋环境噪声研究发展概述及应用前景

海洋环境噪声是海洋声场的背景场,通常被当作干扰项。在传统的水声学和海洋声学中,对海洋环境噪声的研究目的大多是为了降低或抑制环境噪声对水下设备的干扰,提高水下设备的性能和作用距离。目前,许多国家纷纷投入力量,开展海洋环境噪声数据获取、分析及噪声场建模工作。从另一个角度考虑,海洋环境噪声是海洋中永恒存在的声场,包含了水体及海底海面等环境特性信息。因此,可利用海洋环境噪声来研究海洋环境物理特性,通过低代价换取丰富的海洋声学信息。若能对海洋环境噪声的宽频带和任意时间存在的特性加以利用,则可以从海洋环境噪声中提取出相关的海洋环境参数。     

利用海洋环境噪声估计海流流速

为了观测海流在短时间尺度上的变化,基于被动声层析原理,提出了一种利用浅海海洋环境噪声估计海流流速的方法.通过波束形成增加噪声互相关函数的能量积累,从环境噪声互相关函数提取出两个水平阵列间的经验格林函数,利用经验格林函数的时间到达结构反演阵列间的浅海海流流速.海上实验数据处理结果表明,该方法提取了2h时间平均的经验格林函...