Model/data comparison of typhoon-generated noise

Ocean noise recorded during a typhoon can be used to monitor the typhoon and investigate the mechanism of the windgenerated noise. An analytical expression for the typhoon-generated noise intensity is derived as a function of wind speed.A "bi-peak" structure was observed in an experiment during which typhoon-generated noise was recorded. Wind speed dependence and frequency dependence were also observed in the frequency range of 100 Hz–1000 Hz. The model/data comparison shows that results of the present model of 500 Hz and 1000 Hz are in reasonable agreement with the experimental data, and the typhoon-generated noise intensity has a dependence on frequency and a power-law dependence on wind speed.     

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。      

The effects of the ocean surface wave spectrum on low frequency ambient noise in deep water

An ocean surface wave spectrum which is used for low frequency ambient noise in deep water is proposed. It explains the mechanism of low frequency ambient noise from the theoretical relation between the spectrum of sound pressure and wave. Combining the surface wave spectrum and local wind speed in deep water, a theoretical expression of low frequency ambient noise is obtained with wave generated noise theory. Simulation results show that the wave spectrum is crucial to the intensity and the spectral slope of radiated noise spectrum,and the theoretical noise spectrum could be used to predict the ambient noise in deep water.The predicting results axe verified through the experimental data recorded by an ocean bottom seismometer that was deployed on the floor of deep water in April 2016. It is observed that the statistical noise levels from the experimental data for frequencies from 1 Hz to 100 Hz are larger than 70 dB, and the low frequency ambient noise spectrum follows the shape of inverted"N",the valley of noise spectrum is at 3-4 Hz, and the noise intensity is 70 dB. The peak of noise spectrum is at 50 Hz, and the noise intensity is 92 dB. The correlation coefficient is 0.95 between the model spectrum and measured data.     

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。      

Wind dependence of ambient noise in shallow water of Bay of Bengal

This work reports on investigations into the wind dependence of ambient noise in the Bay of Bengal. Ambient noise measurements were made in the shallow water of Bay of Bengal using a portable broadband, high frequency data acquisition system together with a sensitive hydrophone suspended from the measuring platform at a depth of 5 m from the surface where the ocean depth was 25 m. Periodic measurements were carried out for one year corresponding to a wind speed range between 2 m/s and 9 m/s during summer, monsoon and winter seasons. The proportionality of the noise level with wind speed for frequencies ranging from 500 Hz to 6 kHz for each season was studied. The analysis reveals that the correlation between the wind speed and the ambient noise spectrum level was higher at lower frequencies. The results of empirical fitting based on analysis were used for noise level prediction and the model predictions compare well with the measured noise level. Further it was observed that the wind generated noise level measured during summer was approximately 8 dB less than that in other seasons. On the other hand the proportionality between the noise level and the wind speed was less during winter.     

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.     

岛礁海域海洋环境噪声垂直分布和垂直指向性

依据岛礁海域复杂海底地形、海试期间航船分布和实测风速数据,应用射线声传播理论,建立岛礁海域海洋环境噪声三维模型。在海试岛礁海域深海声道条件下,采用射线3D算法,仿真计算了32元垂直测量阵所处265~885 m负声速梯度深度范围内1 kHz风关和50 Hz远处航船海洋环境噪声级垂直分布,以及50 Hz航船海洋环境噪声垂直指向性,并与实测分析进行比较。结果表明,仿真结果与海试实测数据一致性良好。在本例海底起伏、接收点周边存在众多岛礁和海底山的三维环境中,1 kHz风关海洋环境噪声级随深度分布较近于均匀;西南方向较远处航道区海域海底较平坦,航道区至接收阵为缓斜坡海底,50 Hz远处航船海洋环境噪声级随深度有所增加,其噪声垂直指向性无明显水平凹槽。文中建立的岛礁海域海洋环境噪声三维模型,可较好地表征本例岛礁复杂地形海底起伏海域的风关和航船海洋环境噪声级的垂直分布、及航船环境噪声的垂直指向性,实测和仿真的岛礁海域海洋环境噪声相关数据,可供实际应用及相关研究参考。      

次声管道降噪滤波器优化设计

提出了基于声学响应模型与群差分进化算法的次声管道降噪滤波器优化设计方法,在理想条件和工程实践两种情景下设计了管道滤波器的结构参数并仿真分析了降噪性能表现。结果表明:（1）理想条件下的设计结果在约0.1～0.8 Hz的频带内取得了5 dB以上的降噪性能提升,最大提升达到12 dB。（2）工程实践情景的设计结果在各种环境风速中最大可以取得约3dB的性能提升。（3）大风速条件的优化设计可应用于环境风速未知或变化较大的场景。分析结果表明所提设计方法可以有效设计管道滤波器,优化设计的管道滤波器在降噪性能上优于传统管道滤波器。      

南海深海风生噪声特性分析及其噪声源模型修正

基于2015年秋季南海深海区域43天的观测噪声与同步风速预报数据,研究南海风占主导海洋环境噪声风关特性,并对风生噪声源级公式进行修正。本地风速在3~14 m/s范围内变化时,在频段0.5~1.28 kHz,噪声强度近似正比于风速对数的2倍。据此关系,获得不同风速条件下的风生噪声谱级。将Harrison风生噪声源级公式和海面噪声传输模型结合,构建深海风生噪声数值计算模型,通过求取最优的风生噪声源级公式系数项,使得在风占主导频段和风速范围内实验谱级与数值结果误差平方和最小,对Harrison风生噪声源级公式进行修正,并使其适用频段范围拓宽两倍。最后,利用南海其它区域实验数据检验模型的适用性,结果表明,模型预报噪声级与实验值吻合度较高,可供预报南海风生海洋环境噪声级实际应用参考。      

Underwater ambient noise on the Chukchi Sea continental slope from 2006-2009

From September 2006 to June 2009, an autonomous acoustic recorder measured ambient noise north of Barrow, Alaska on the continental slope at 235 m depth, between the Chukchi and Beaufort Seas. Mean monthly spectrum levels, selected to exclude impulsive events, show that months with open-water had the highest noise levels (80-83 dB re: 1 μPa(2)/Hz at 20-50 Hz), months with ice coverage had lower spectral levels (70 dB at 50 Hz), and months with both ice cover and low wind speeds had the lowest noise levels (65 dB at 50 Hz). During ice covered periods in winter-spring there was significant transient energy between 10 and 100 Hz from ice fracture events. During ice covered periods in late spring there were significantly fewer transient events. Ambient noise increased with wind speed by ~ 1 dB/m/s for relatively open-water (0%-25% ice cover) and by ~ 0.5 dB/m/s for nearly complete ice cover (> 75%). In September and early October for all years, mean noise levels were elevated by 2-8 dB due to the presence of seismic surveys in the Chukchi and Beaufort Seas.     

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.     

Masked auditory thresholds in sciaenid fishes: a comparative study

Western Atlantic sciaenids comprise a taxonomically diverse teleost family with significant variations in the relationship between the swim bladder and the otic capsule. In this study, the auditory brainstem response (ABR) was used to test the hypothesis that fishes with different peripheral auditory structures (black drum, Pogonias chromis and Atlantic croaker, Micropogonias undulatus) show differences in frequency selectivity. In a black drum the swim bladder is relatively distant from the otic capsule while the swim bladder in Atlantic croaker possesses anteriorly-directed diverticulas that terminate relatively near the otic capsule. Signals were pure tones in the frequency range, 100 Hz to 1.5 kHz, and thresholds were determined both with and without the presence of simultaneous white noise at two intensity levels (124 dB and 136 dB, re: 1 microPa). At the 124 dB level of white noise background, both the black drum and Atlantic croaker showed similar changes in auditory sensitivity. However, in the presence of the 136 dB white noise masker, black drum showed significantly greater shifts in auditory thresholds between 300 and 600 Hz. The results indicate that the two species differ in frequency selectivity since the Atlantic croaker was less susceptible to auditory threshold shifts, particularly at the higher level of masking. This difference may be linked to peripheral auditory mechanisms.     

台风激发水下噪声场的建模及其在台风风速反演中的应用

基于简正波理论,结合风成海面噪声传播模型和风成噪声源级模型,推导出台风激发水下噪声场强度的计算公式,建立水下噪声强度与海表面风速的函数关系,并给出模型中相关参数的求解方法。应用这一关系,由台风经过时的水下噪声实测数据,反演得到对应时刻的海表面风速值,并将反演结果与气象台给出的台风风速预报值进行对比。      

Ocean dynamic noise energy flux directivity in the 400 Hz to 700 Hz frequency band

Results of field studies of underwater dynamic noise energy flux directivity at two wind speeds, 6 m/s and 12 m/s, in the 400 Hz to 700 Hz frequency band in the deep open ocean are presented. The measurements were made by a freely drifting telemetric combined system at 500 m depth. Statistical characteristics of the horizontal and vertical dynamic noise energy flux directivity are considered as functions of wind speed and direction. Correlation between the horizontal dynamic noise energy flux direction and that of the wind was determined; a mechanism of the horizontal dynamic noise energy flux generation is related to the initial noise field scattering on ocean surface waves.     

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。      

Effects of roving level variation on monaural detection with a contralateral cue.

Monaural detection with a contralateral cue (MDCC) was measured with and without a 20-dB overall roving level to determine the contribution of loudness to performance on this task. Psychometric functions were obtained for three normal-hearing subjects as a function of the signal-to-noise ratio for pure-tone and 1/3-oct noiseband signals at 500 and 4000 Hz with a wideband noise masker. At 4000 Hz, the roving level degrades performance for the narrow-band noise signal by about 5.3 dB. In addition, the presence of the contralateral cue degrades performance for both the pure-tone and narrow-band noise signals at 4000 Hz by 3 to 6 dB. At 500 Hz, however, performance is not affected by the roving level, and is improved by 3 to 6 dB by the contralateral cue. These results indicate that loudness is being used as a cue only for detection of the 4000-Hz narrow-band noise.     

Monaural envelope correlation perception, revisited: effects of bandwidth, frequency separation, duration, and relative level of the noise bands

This article presents the results of two experiments investigating performance on a monaural envelope correlation discrimination task. Subjects were asked to discriminate pairs of noise bands that had identical envelopes (referred to as correlated stimuli) from pairs of noise bands that had envelopes which were independent (uncorrelated stimuli). In the first experiment, a number of stimulus parameters were varied: the center frequency of the lower frequency noise band in a pair, f1; the frequency separation between component noise bands; the duration of the stimuli; and the bandwidth of the component noise bands. For a long stimulus duration (500 ms) and a relatively wide bandwidth (100 Hz), subjects could easily discriminate correlated from uncorrelated stimuli for a wide range of frequency separations between the component noise bands. This was true both when f1 was 350 Hz, and when f1 was 2500 Hz. In each case, narrowing the bandwidth to 25 Hz, or shortening the duration to 100 ms, or both, made the task more difficult, but not impossible. In the second experiment, the level of the higher frequency noise band in a pair was varied. Performance did not decrease monotonically as the level of this band was decreased below the level of the other band, and only showed marked impairment when the level of the higher frequency band was at least 60 dB below that of the lower frequency band. The pattern of results in these two experiments is different from that which is obtained when the same stimulus parameters are varied in experiments investigating comodulation masking release (CMR). This suggests that the mechanisms underlying CMR and those underlying the discrimination of envelope correlation are not identical.     

Ambient noise in large rivers (L)

This paper presents the results of hydroacoustic noise research in three large European rivers: the Danube, the Sava, and the Tisa. Noise in these rivers was observed during a period of ten years, which includes all annual variation in hydrological and meteorological conditions (flow rate, speed of flow, wind speed, etc.). Noise spectra are characterized by wide maximums at frequencies between 20 and 30 Hz, and relatively constant slope toward higher frequencies. Spectral level of noise changes in time in relatively wide limits. At low frequencies, below 100 Hz, the dynamics of noise level is correlated with the dynamics of water flow and speed. At higher frequencies, noise spectra are mostly influenced by human activities on river and on riverbanks. The influence of wind on noise in rivers is complex due to the annual variation of river surface. The influence of wind is less pronounced than in oceans, seas, and lakes.