非均匀海洋环境噪声中的匹配场处理舰船辐射噪声级估计方法

在实际舰船辐射噪声测量过程中,受非均匀海洋环境噪声的影响,导致常规测量方法的性能急剧下降,基于此,提出了一种非均匀海洋环境噪声背景中的垂直阵舰船辐射噪声测量方法。根据水声信道传播理论,建立了由海面多个空时独立均匀分布噪声源构成的非均匀背景噪声场模型,推导了非均匀海洋环境噪声场中垂直阵舰船辐射噪声估计的理论公式。针对典型的浅海水声信道,进行计算机仿真实验,分析了该方法的测量性能并与常规匹配场测量方法进行对比,结果表明:(1)该方法能有效克服非均匀海洋环境噪声对测量结果的影响,测量误差较小;(2)相同测量条件下,该方法测量性能优于常规匹配场舰船辐射噪声级测量方法;(3)当信噪比满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。      

非均匀海洋环境噪声中的匹配场处理舰船辐射噪声级估计方法

在实际舰船辐射噪声测量过程中,受非均匀海洋环境噪声的影响,导致常规测量方法的性能急剧下降,基于此,提出了一种非均匀海洋环境噪声背景中的垂直阵舰船辐射噪声测量方法。根据水声信道传播理论,建立了由海面多个空时独立均匀分布噪声源构成的非均匀背景噪声场模型,推导了非均匀海洋环境噪声场中垂直阵舰船辐射噪声估计的理论公式。针对典型的浅海水声信道,进行计算机仿真实验,分析了该方法的测量性能并与常规匹配场测量方法进行对比,结果表明:(1)该方法能有效克服非均匀海洋环境噪声对测量结果的影响,测量误差较小;(2)相同测量条件下,该方法测量性能优于常规匹配场舰船辐射噪声级测量方法;(3)当信噪比满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。     

匹配场处理舰船辐射噪声级估计方法

针对水声信道对舰船辐射噪声声传播的影响,进而导致声源级测量结果不准确的问题,提出了基于匹配场处理的舰船辐射噪声级估计方法。在海洋环境噪声为空间均匀高斯白噪声的假设下,当海洋环境参数已知、信噪比满足一定要求时,匹配场处理能有效地给出被测噪声源的位置信息及该位置处的能量响应。从能量估计角度出发,推导了声源位置处匹配场输出响应的能量修正因子计算公式,从理论上证明了匹配场处理在被测声源位置处输出响应与能量修正因子的乘积为真实声源级的最小方差无偏(MVU)估计。该方法首先选择合适的声场计算模型计算拷贝场向量,对接收到的辐射噪声信号进行匹配场处理,得出接收信号级和被测声源位置;其次利用该位置所对应的拷贝场向量替换能量修正因子公式中的真实信道传输函数以计算能量修正因子的估计值;最后由接收信号级与能量修正因子估计值相乘得出舰船辐射噪声声源级的MVU估计。针对典型的浅海水声信道,进行了计算机仿真试验,结果表明:该方法能有效地进行舰船辐射噪声测量,当信噪比满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。      

水下声学滑翔机用于东印度洋声传播特性分析及声源估计

常规实验方法无法同步获取深海大尺度声学和水文数据,水下滑翔机可作为同步观测平台解决该问题.首先利用在东印度洋北部海域水下滑翔机同步获取的声传播和水文实验数据,分析了水下滑翔机的自噪声谱级和实验海区声传播特性,然后推算并修正了滑翔机水下运动轨迹,利用第一影区水下滑翔机接收声传播信号的脉冲多途到达时间差对声源进行测距与定深。潜标接收噪声与滑翔机自噪声谱级对比表明,水下滑翔机在海洋中无动力运动时的系统自噪声接近于潜标观测的海洋环境噪声。滑翔机实测的声传播损失与模型计算结果吻合较好,第一影区水下声源测距定深结果与实际位置较为一致,测距与定深的相对误差均小于5%。利用加载水听器的水下滑翔机可以实现水文环境数据与声学信号的同步观测,对深海声传播特性测量及定位算法研究具有重要意义。      

人工头近场头相关传输函数及其特性

采用球形正十二面体声源及其空间定位系统,测量并建立了KEMAR人工头的近场头相关传输函数(HRTF)数据库。基于数据库分析了近场HRTF在频域和时域随声源距离变化的规律;讨论了用近场HRTF算得的双耳声级差(TLD)和双耳时间差(ITD)所包含的声源距离定位信息。结果表明,测量系统和所得数据具有较好的重复性和准确性,保留了1 kHz以下的低频定位信息。并且,近场HRTF幅度谱和ILD随声源距离的变化明显;用相关法算得2 kHz以下频段的ITD随声源距离略有变化。本文数据库及其分析结果将为声源距离定位的应用提供基础。      

基于虚拟时间反转镜的垂直阵舰船辐射噪声级测量方法

研究了利用垂直阵测量舰船辐射噪声过程中因水声信道的多径效应对测量性能产生的影响,建立了基于声场模型的舰船辐射噪声测量的数学模型,推导了基于虚拟时间反转镜辐射噪声测量的理论公式,提出了一种基于虚拟时间反转镜技术的垂直阵舰船辐射噪声级测量方法。该方法首先采用基于波束积分的SCOOTER模型,根据海洋环境参数计算出辐射声源至测量水听器之间的信道传输函数,然后,用计算出的信道传输函数对接收信号做虚拟时反处理,以消除或减弱信道多径效应对接收信号的影响,从而提高舰船辐射噪声级测量精度。针对典型的浅海声信道,进行了计算机仿真试验。结果表明,该方法能有效地进行舰船宽带辐射噪声测量,当阵元个数满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。      

稀疏贝叶斯学习远近场混合源定位方法

针对远、近场混合源定位,提出一种基于稀疏重构理论框架的远、近场混合源分离和定位算法。该算法充分考虑平面波导向矢量和球面波导向矢量的相关特性,利用远、近场声源在阵列上的响应机理的差异,针对远、近场区域分别构造过完备字典,采用多测量矢量模型下的稀疏贝叶斯学习算法重构远近场混合源的空间谱,同时完成远近场混合源的分离和定位。本文算法可以在半波长间距布放的线列阵下对混合源进行定位,适用于高斯和非高斯信号,且无需信源数和噪声功率等先验信息,并具有较高的分辨力和定位精度·计算机仿真结果验证了算法的有效性。      

PB-1型窄脉冲压电薄膜可逆式换能器

本文著者研制成PB-1型PVDF可逆式压电换能器。它的通频带较宽,中心频率500—900KHz,通带Q值1.5,发送电压响应[级]148.9dB(re:1μPa/V),灵敏度-210dB(re:1V/μPa)。在水中声脉冲持续时间7—10μs,并有足够的声功率输出,电声效率约10％。 本文介绍了该换能器的结构、理论分析、测量结果及应用效果。证明了理论与实验的一致性。可供电声、水声、超声等其它PVDF传感器设计时参考。     

空气中声源的水下匹配场定位

通过水下布放的垂直线列阵采集空中声源在水下激发的测量声场,采用声场波数积分模型(OASES模型)对空中声源激发的水下声场建模,计算出拷贝声场,将二者进行匹配处理从而对空中声源目标定位。首先通过数值仿真验证了匹配场处理技术对空中声源的测距能力,并通过引入宽带匹配场处理器平滑掉距离上的周期性旁瓣。最后分析南海某海域的空气声试验数据,采用常规匹配场方法对700 m以内的32组空中声源目标进行定位,测距结果与GPS计算的收发间实际距离相比,大多数情况下是一致的,在较远距离由于信噪比降低,测量结果容易出现偏差。     

用垂直阵和单水听器测量水下目标辐射噪声的误差分析及其修正方法

文章给出了水声波导模型下垂直阵和单水听器测量水下目标辐射噪声的误差和修正方法,以便使两种测量结果一致和统一。在设定典型水声波导的参数后,用波数积分方法计算出声源到垂直阵各阵元的信道传输函数,再推导出垂直嵌套阵聚焦波束的信道传输函数,从而得到单水听器和垂直嵌套阵的测量误差。数值计算表明在70 m海深条件下,不同深度单水听器测量单频信号频谱级起伏达15 dB以上,总声级测量误差的均值为3 dB,而垂直嵌套阵测量单频信号频谱级起伏仅4 dB,总声级测量误差的均值趋于0 dB。海上实验测量单频信号声源级的结果与数值计算的起伏一致,海试中垂直阵获得较高的空间增益。结论是在浅海条件下垂直阵的测量精度高于单水听器的测量精度,用单水听器测量的目标总声级需要修正时可以修正,而用单水听器测量的单频信号声源级则难以修正。     

In situ source level and source position estimates of biological transient signals produced by snapping shrimp in an underwater environment.

Biological transient signals produced by snapping shrimp are sensed underwater by a wide aperture array. The instantaneous range and bearing of the source position of each snap is estimated along with a source level equal to the peak-to-peak amplitude of the pressure impulse generated by the snap at a standard distance of 1 m from its point of origin. For a sample of 1000 snaps recorded in Sydney Harbour, the distribution of peak-to-peak sound pressure levels has a mean value of 187 dB (re 1 microPa) and an interquartile range of 185-189 dB (re 1 microPa). Plotting the Cartesian coordinates of the source positions of the biological transient signals over a period of time maps the two-dimensional spatial distribution of the local snapping shrimp population. The principal habitat is found to be geocoincident with a 120-m-long wharf, the closest point of which is 60 m from the middle of the receiving array. The passive ranging performance of the wide aperture array is evaluated by generating mechanical transient signals at selected positions along the wharf. Precise estimates of the relative times-of-arrival of the acoustic wavefronts lead to source range and bearing estimates with standard deviations of only 0.1 m and 0.005 degrees (respectively), in agreement with theoretical predictions.     

Underwater radiated noise from modern commercial ships

Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (<1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1 μPa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1 μPa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e.g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments.     

Ambient noise imaging in warm shallow waters; robust statistical algorithms and range estimation

The high frequency ambient noise in warm shallow waters is dominated by snapping shrimp. The loud snapping noises they produce are impulsive and broadband. As the noise propagates through the water, it interacts with the seabed, sea surface, and submerged objects. An array of acoustic pressure sensors can produce images of the submerged objects using this noise as the source of acoustic "illumination." This concept is called ambient noise imaging (ANI) and was demonstrated using ADONIS, an ANI camera developed at the Scripps Institution of Oceanography. To overcome some of the limitations of ADONIS, a second generation ANI camera (ROMANIS) was developed at the National University of Singapore. The acoustic time series recordings made by ROMANIS during field experiments in Singapore show that the ambient noise is well modeled by a symmetric α-stable (SαS) distribution. As high-order moments of SαS distributions generally do not converge, ANI algorithms based on low-order moments and fractiles are developed and demonstrated. By localizing nearby snaps and identifying the echoes from an object, the range to the object can be passively estimated. This technique is also demonstrated using the data collected with ROMANIS.     

Comodulation masking release in bottlenose dolphins (Tursiops truncatus)

The acoustic environment of the bottlenose dolphin often consists of noise where energy across frequency regions is coherently modulated in time (e.g., ambient noise from snapping shrimp). However, most masking studies with dolphins have employed random Gaussian noise for estimating patterns of masked thresholds. The current study demonstrates a pattern of masking where temporally fluctuating comodulated noise produces lower masked thresholds (up to a 17 dB difference) compared to Gaussian noise of the same spectral density level. Noise possessing wide bandwidths, low temporal modulation rates, and across-frequency temporal envelope coherency resulted in lower masked thresholds, a phenomenon known as comodulation masking release. The results are consistent with a model where dolphins compare temporal envelope information across auditory filters to aid in signal detection. Furthermore, results suggest conventional models of masking derived from experiments using random Gaussian noise may not generalize well to environmental noise that dolphins actually encounter.     

Blue and fin whale call source levels and propagation range in the Southern Ocean

Blue (Balaenoptera musculus) and fin whales (B. physalus) produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200 km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56 km. The error in range measurements was 3.8 km using hyperbolic localization, and 3.4 km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189+/-3 dB re:1 microPa-1 m over 25-29 Hz, and the average fin whale call source level was 189+/-4 dB re:1 microPa-1 m over 15-28 Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales.     

North Pacific right whale up-call source levels and propagation distance on the southeastern Bering Sea shelf

Call source levels, transmission loss, and ambient noise levels were estimated for North Pacific right whale (Eubalaena japonica) up-calls recorded in the southeastern Bering Sea in autumn of 2000 and 2001. Distances to calling animals, needed to estimate source levels, were based on two independent techniques: (1) arrival-time differences on three or more hydrophones and (2) shallow-water dispersion of normal modes on a single receiver. Average root-mean-square (rms) call source levels estimated by the two techniques were 178 and 176 dB re 1 μPa at 1 m, respectively, over the up-call frequency band, which was determined per call and averaged 90 to 170 Hz. Peak-to-peak source levels were 14 to 22 dB greater than rms levels. Transmission loss was approximately 15?log(10)(range), intermediate between cylindrical and spherical spreading. Ambient ocean noise within the up-call band varied from 72 to 91 dB re 1 μPa(2)/Hz. Under average noise conditions, call spectrograms were detectable for whales at distances up to 100 km, but propagation and detection distance may vary depending on environmental parameters and anthropogenic noise. Obtaining distances to animals and acoustic detection range is a step toward using long-term passive acoustic recordings to estimate abundance for this critically endangered whale population.     

NUMERICAL MODELLING OF MEDIAN ROAD TRAFFIC NOISE BARRIERS

Outdoor sound propagation from road traffic is modelled by solving a boundary integral equation formulation of the wave equation using boundary element techniques in two dimensions. In the first model, the source representing a traffic stream can be considered as a coherent line source of sound. The results can then be transformed to derive a pseudo-three dimensional solution to the problem. In the second model the line source is incoherent. For receivers near the ground, the second model predicted significantly higher values of ground attenuation than the first. The first model generally produced better agreement with ground attenuation results obtained using the U.K. traffic noise prediction model. For conditions when a noise barrier was present and the ground was absorbent, the incoherent line source model generally predicted significantly higher values of attenuation than those from the barrier and ground attenuation calculated separately. Over a range of receiver positions and barrier heights a similar, but less marked effect was observed when the coherent line source model was used. On dual carriageway roads, it is possible to incorporate barriers on the central reservation as a noise control measure. These are “median” noise barriers. The incoherent line source model is used to assess the performance of median barriers in reducing noise when installed alone and also with associated roadside barriers. A sound absorbent median noise barrier 1m in height produced consistent values of insertion loss of between 1 and 2dB over the range of receiver positions and ground conditions considered. When the median barrier was used in conjunction with a roadside barrier it produced a consistent improvement in insertion loss of between 1 and 2 dB over the range of conditions considered.     

Effects of noise levels and call types on the source levels of killer whale calls

Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking noise reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to noise exposure is also needed for such assessment. Prior studies have reported variations in the source levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking noise by increasing their call amplitude. The objectives of the current study were to investigate the source levels of a variety of call types in southern resident killer whales while also considering background noise level as a likely factor related to call source level variability. The source levels of 763 discrete calls along with corresponding background noise were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both noise level and call type were significant factors on call source levels (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking noise reduces vocal communication space in marine mammals.     

Measurement of an individual silver perch Bairdiella chrysoura sound pressure level in a field recording

Simultaneous audio and video were recorded of a silver perch Bairdiella chrysoura producing its characteristic drumming sound in the field. The background noise contribution to the total sound pressure level is estimated using sounds that occurred between the pulses of the silver perch sound. This background contribution is subtracted from the total sound to give an estimate of the sound pressure level of the individual fish. A silver perch source level in the range 128-135 dB (re: 1 microPa) is obtained using an estimate of the distance between the fish and the hydrophone. The maximum distance at which an individual silver perch could be detected depends on the background sound level as well as the propagation losses. Under the conditions recorded in this study, the maximum detection distance would be 1-7 m from the hydrophone.     

Echolocation signals of free-ranging killer whales (Orcinus orca) and modeling of foraging for chinook salmon (Oncorhynchus tshawytscha)

Fish-eating "resident"-type killer whales (Orcinus orca) that frequent the coastal waters off northeastern Vancouver Island, Canada have a strong preference for chinook salmon (Oncorhynchus tshawytscha). The whales in this region often forage along steep cliffs that extend into the water, echolocating their prey. Echolocation signals of resident killer whales were measured with a four-hydrophone symmetrical star array and the signals were simultaneously digitized at a sample rate of 500 kHz using a lunch-box PC. A portable VCR recorded the images from an underwater camera located adjacent to the array center. Only signals emanating from close to the beam axis (1185 total) were chosen for a detailed analysis. Killer whales project very broadband echolocation signals (Q equal 0.9 to 1.4) that tend to have bimodal frequency structure. Ninety-seven percent of the signals had center frequencies between 45 and 80 kHz with bandwidths between 35 and 50 kHz. The peak-to-peak source level of the echolocation signals decreased as a function of the one-way transmission loss to the array. Source levels varied between 195 and 224 dB re: 1 microPa. Using a model of target strength for chinook salmon, the echo levels from the echolocation signals are estimated for different horizontal ranges between a whale and a salmon. At a horizontal range of 100 m, the echo level should exceed an Orcinus hearing threshold at 50 kHz by over 29 dB and should be greater than sea state 4 noise by at least 9 dB. In moderately heavy rain conditions, the detection range will be reduced substantially and the echo level at a horizontal range of 40 m would be close to the level of the rain noise.