印太瓶鼻海豚(Tursiops aduncus)通讯声信号分类及特征参数的环境差异性分析

通过长期记录室内水池环境下两只印太瓶鼻海豚通讯信号,并与海湾自然环境下同样的两只海豚所发出的通讯信号进行比较分析,从信号类型、声谱特征等方面研究生活环境变化下瓶鼻海豚通讯信号的差异性。结果表明,生活环境的差异,会改变瓶鼻海豚通讯信号。海湾自然环境下,瓶鼻海豚通讯信号以正弦型信号为主;而室内水池环境下,上扫型信号比例明显增多,而正弦型信号减少。两种环境下,瓶鼻海豚通讯信号在持续时间、拐点数、起始频率、结束频率、最小频率、最大频率等存在显著性差异(p<0.05),但信号的频率变化量相近(p=0.29)。结果为提高海豚通讯信号认知和增强海豚生物行为研究提供一定的科学参考,同时也为仿生隐蔽通信提供技术支撑。      

时频特征的海豚发声端点检测方法研究*

为在复杂的海洋环境噪声场中检测出目标海豚的某类声信号,设计了一种基于海豚声学特征的端点检测方法。根据海洋环境中噪声能量大且分布频率范围广,而海豚声音的时频特征具有持续时间短,、频率高且集中,、发声行为持续时间长的特点,将采集到的海洋声音进行分帧,计算单帧信号短时能量、谱质心和谱质心二阶偏移率,当海豚发出声信号时,谱质心和能量相应发生突变,截取发生突变的信号实现端点检测。通过与门限法等其他常见端点检测方法进行对比,结果表明,此方法在低信噪比的海洋环境下对单一海豚的某一类声信号检测准确度更高,同时具有较强的抗干扰能力。     

基于激光水下爆炸声源的声探测技术

基于激光水下爆炸的声探测技术,设计了激光声水下目标探测器。对激光水下爆炸声源的产生机理进行研究,并开展水下探测器发射声信号检测的实验。实验结果表明:强脉冲激光聚焦于水介质产生爆炸性球面声源,探测器内部的声反射面将球面声信号转变为高指向性的平面波信号。通过对探测器的发射信号和接收的目标回波信号进行数值计算,得到探测器发射信号具有波束指向性窄、距离分辨力高和探测距离远等特点,满足水下目标探测的应用需求。     

一种利用海豚叫声的仿生水声通信方法

针对水下通信隐蔽性的需求, 克服传统固定载波调制方式带来的声源暴露问题, 提出一种基于海豚叫声的仿生伪装水声通信方法, 使通信信号被当作海洋生物噪声排除, 达到隐蔽通信的效果. 研究了海豚叫声信号特点, 利用海豚哨声信号实现同步与识别, 采用差分脉冲位置调制方法, 信息调制在相邻海豚嘀嗒声信号的时间间隔, 采用压缩传感体制下的匹配追踪技术估计信道, 虚拟时反技术实现信道均衡. 湖试结果验证了该方法的有效性和可行性, 接收声信号与发射信号声音上具有很高的相似度, 可以达到伪装隐蔽的效果. 实验中水平距离2 km, 通信速率不小于29 bps时,误码率可以达到10^-4以下. 关键词： 水声通信 仿生 海豚 隐蔽     

基于Hilbert变换的水下多源声信号频率的相干探测

为实现水下中低频声信号的探测识别,通过研究水下多声源相干探测信号的特征,理论上给出了相干探测信号频谱混叠情况下的特征表达式,并提出了一种基于Hilbert变换的信号解调处理方法,实现了水下多声源相干探测信号频谱混叠情况下各声源发声频率的解调.该方法将探测信号经过滤波平滑处理之后进行Hilbert变换,得到信号的解析形式,然后对解析信号模值的平方进行二次滤波平滑等处理,分离混叠在一起的频带,将得到的信号进行频谱分析,根据频移值计算得到水下各个声源的发声频率.在光学暗室下搭建激光相干探测系统,对2~6kHz的水下声信号进行实验,实验结果表明,该方法可以有效分离探测信号中混叠在一起的信号频带,并准确提取各水下声信号的发声频率,频率提取重复性不大于2.5Hz.     

空气中声源激发的浅海水下声场传播实验研究

为了了解空气中声源激发的水下声场传播特性,对此开展实验研究.2010年在南海北部海域进行了一次空气中声源激发水下声场实验,在水下成功地接收到远至4 km处大功率扬声器在空中发射的脉冲声信号.本文通过分析实验数据,研究空气中声源激发的浅海水下声场传播特点.针对接收阵拾取的声传播信号信噪比低的特点,综合利用脉冲压缩以及波束...     

圈养瓶鼻海豚通讯信号分析及融合分类方法

针对圈养条件下瓶鼻海豚通讯信号（whistle）分类时混叠大量回声定位信号（click）导致分类正确率降低的问题,提出了一种基于机器学习的融合分类方法。分别提取whistle信号的时频分布特征训练随机森林分类器,梅尔时频图特征训练卷积神经网络分类器,在此基础上设计融合判决器对混叠whistle信号进行分类识别。对圈养海豚声信号采集实验数据的分类识别结果表明,融合分类方法具有更好的分类性能,对混叠whistle信号分类正确率大于94%,优于时频分布特征分类器和梅尔时频图特征分类器,能够提高混叠信号的分类能力。      

圈养印太瓶鼻海豚(Tursiops aduncus)正弦型哨叫声与其行为及水环境关系分析

为分析圈养印太瓶鼻海豚与所处水环境间的关系,观测和记录了两只圈养印太瓶鼻海豚一年内的发声、行为及水环境温度、盐度及酸碱度。通过时频滤波和分析,筛选出一年中17:00到08:00内海豚发出的正弦型哨叫声。经统计、比对和相关性分析,得到:正弦型哨叫声发生量与海豚不良情绪行为发生量线性正相关(拟合优度R2=93.89%),8月—10月发生频次最多,此时海豚不良情绪行为也最多;该类型信号发生量占比与所处水环境月平均温度和盐度有关,并拟合出它们的关系式(拟合优度R2=68.61%),但受月平均酸碱度影响不大;水环境月平均温度和盐度在一定范围内时,海豚不良情绪行为发生量占比可以控制在12%以下。研究结果为今后利用海豚哨叫声判断海豚生物行为、健康状况、圈养环境舒适度等提供一定的科学参考。      

水下声音可冲出表面

简单的声波理论曾预言，任何在水下产生的声音都会在水-气交界面处发生反射，而不会发射到空气中去．因此长期以来科学家们相信在海下产生的声音是不可能被水面上探测到的．但最近美国Colorado环境科学联合研究所（Cooperative Institute for Research in Environmental Science，简称CIRES）的0．Godin博士发现简单的声波理论不能描述在水面附近产生的低频噪声波的行为，他利用最新的声波理论计算得出，当声波波长可与声源与水面的距离相比凝或更长时。声源发出的声波可全部发射到空气中．     

基于水下等离子体的脉冲通信发射机

水下声通信是海洋中最主要的通信方式,在时变空变随机多途的恶劣信道中实现可靠的超远程水声通信,是一项亟待解决的难题。论文提出了一种利用水下等离子体脉冲信号、采用脉冲定宽时序编码调制方案的超远程水声通信体制,研制了一种基于水下等离子体的微型脉冲声源,搭建了基于该声源的脉冲通信发射机,实现了入水自动检测、休眠定时切换、发射频率可调、码元调制编码等脉冲通信功能。经水池试验验证,该发射机在Φ60×600mm体积内声源级达217dB,较好地实现预设脉冲信号的发射。     

Behavioral responses of two captive bottlenose dolphins (Tursiops truncatus) to a continuous 50 kHz tone

At present, the fundamental frequencies of signals of most commercially available acoustic alarms to deter small cetaceans are below 20 kHz, but it is not well ascertained whether higher frequencies have a deterrent effect on bottlenose dolphins (Tursiops truncatus). Two captive bottlenose dolphins housed in a floating pen were subjected to a continuous pure tone at 50 kHz with a source level of 160 ± 2 dB (re 1 μPa, rms). The behavioral responses of dolphins were judged by comparing surfacing distance relative to the sound source, number of surfacings, and number of echolocation clicks produced, during forty 15 min baseline periods with forty 15 min test periods (four sessions per day, 40 sessions in total). On all 10 study days, surfacing distance and the number of surfacings increased while click production decreased during broadcasts of test sound. The avoidance threshold sound pressure level for a continuous 50 kHz tone for the bottlenose dolphins, in the context of this study, was estimated to be 144 ± 2 dB (re 1 μPa, rms). The results indicated that a continuous 50 kHz tonal signal can deter bottlenose dolphins from an area.     

Discriminating features of echolocation clicks of melon-headed whales (Peponocephala electra), bottlenose dolphins (Tursiops truncatus), and Gray's spinner dolphins (Stenella longirostris longirostris)

Spectral parameters were used to discriminate between echolocation clicks produced by three dolphin species at Palmyra Atoll: melon-headed whales (Peponocephala electra), bottlenose dolphins (Tursiops truncatus) and Gray's spinner dolphins (Stenella longirostris longirostris). Single species acoustic behavior during daytime observations was recorded with a towed hydrophone array sampling at 192 and 480 kHz. Additionally, an autonomous, bottom moored High-frequency Acoustic Recording Package (HARP) collected acoustic data with a sampling rate of 200 kHz. Melon-headed whale echolocation clicks had the lowest peak and center frequencies, spinner dolphins had the highest frequencies and bottlenose dolphins were nested in between these two species. Frequency differences were significant. Temporal parameters were not well suited for classification. Feature differences were enhanced by reducing variability within a set of single clicks by calculating mean spectra for groups of clicks. Median peak frequencies of averaged clicks (group size 50) of melon-headed whales ranged between 24.4 and 29.7 kHz, of bottlenose dolphins between 26.7 and 36.7 kHz, and of spinner dolphins between 33.8 and 36.0 kHz. Discriminant function analysis showed the ability to correctly discriminate between 93% of melon-headed whales, 75% of spinner dolphins and 54% of bottlenose dolphins.     

Behavioral avoidance threshold level of a harbor porpoise (Phocoena phocoena) for a continuous 50 kHz pure tone

The use of ultrasonic sounds in alarms for gillnets may be advantageous, but the deterring effects of ultrasound on porpoises are not well understood. Therefore a harbor porpoise in a large floating pen was subjected to a continuous 50 kHz pure tone with a source level of 122+/-3 dB (re 1 microPa, rms). When the test signal was switched on during test periods, the animal moved away from the sound source. Its respiration rate was similar to that during baseline periods, when the sound was switched off. The behavior of the porpoise was related to the sound pressure level distribution in the pen. The sound level at the animal's average swimming location during the test periods was approximately 107+/-3 dB (re 1 microPa, rms). The avoidance threshold sound pressure level for a continuous 50 kHz pure tone for this porpoise, in the context of this study, is estimated to be 108+/-3 dB (re 1 microPa, rms). This study demonstrates that porpoises may be deterred from an area by high frequency sounds that are not typically audible to fish and pinnipeds and would be less likely masked by ambient noise.     

Low frequency narrow-band calls in bottlenose dolphins (Tursiops truncatus): signal properties, function, and conservation implications

Dolphins routinely use sound for social purposes, foraging and navigating. These sounds are most commonly classified as whistles (tonal, frequency modulated, typical frequencies 5-10 kHz) or clicks (impulsed and mostly ultrasonic). However, some low frequency sounds have been documented in several species of dolphins. Low frequency sounds produced by bottlenose dolphins (Tursiops truncatus) were recorded in three locations along the Gulf of Mexico. Sounds were characterized as being tonal with low peak frequencies (mean?=?990 Hz), short duration (mean?=?0.069 s), highly harmonic, and being produced in trains. Sound duration, peak frequency and number of sounds in trains were not significantly different between Mississippi and the two West Florida sites, however, the time interval between sounds within trains in West Florida was significantly shorter than in Mississippi (t?=?-3.001, p?=?0.011). The sounds were significantly correlated with groups engaging in social activity (F=8.323, p=0.005). The peak frequencies of these sounds were below what is normally thought of as the range of good hearing in bottlenose dolphins, and are likely subject to masking by boat noise.     

Source parameters of echolocation clicks from wild bottlenose dolphins (Tursiops aduncus and Tursiops truncatus)

The Indian Ocean and Atlantic bottlenose dolphins (Tursiops aduncus and Tursiops truncatus) are among the best studied echolocating toothed whales. However, almost all echolocation studies on bottlenose dolphins have been made with captive animals, and the echolocation signals of free-ranging animals have not been quantified. Here, biosonar source parameters from wild T. aduncus and T. truncatus were measured with linear three- and four-hydrophone arrays in four geographic locations. The two species had similar source parameters, with source levels of 177-228 dB re 1 μPa peak to peak, click durations of 8-72 μs, centroid frequencies of 33-109 kHz and rms bandwidths between 23 and 54 kHz. T. aduncus clicks had a higher frequency emphasis than T. truncatus. The transmission directionality index was up to 3 dB higher for T. aduncus (29 dB) as compared to T. truncatus (26 dB). The high directionality of T. aduncus does not appear to be only a physical consequence of a higher frequency emphasis in clicks, but may also be caused by differences in the internal properties of the sound production system.     

Receiving beam patterns in the horizontal plane of a harbor porpoise (Phocoena phocoena)

Receiving beam patterns of a harbor porpoise were measured in the horizontal plane, using narrow-band frequency modulated signals with center frequencies of 16, 64, and 100 kHz. Total signal duration was 1000 ms, including a 200 ms rise time and 300 ms fall time. The harbor porpoise was trained to participate in a psychophysical test and stationed itself horizontally in a specific direction in the center of a 16-m-diameter circle consisting of 16 equally-spaced underwater transducers. The animal's head and the transducers were in the same horizontal plane, 1.5 m below the water surface. The go/no-go response paradigm was used; the animal left the listening station when it heard a sound signal. The method of constants was applied. For each transducer the 50% detection threshold amplitude was determined in 16 trials per amplitude, for each of the three frequencies. The beam patterns were not symmetrical with respect to the midline of the animal's body, but had a deflection of 3-7 degrees to the right. The receiving beam pattern narrowed with increasing frequency. Assuming that the pattern is rotation-symmetrical according to an average of the horizontal beam pattern halves, the receiving directivity indices are 4.3 at 16 kHz, 6.0 at 64 kHz, and 11.7 dB at 100 kHz. The receiving directivity indices of the porpoise were lower than those measured for bottlenose dolphins. This means that harbor porpoises have wider receiving beam patterns than bottlenose dolphins for the same frequencies. Directivity of hearing improves the signal-to-noise ratio and thus is a tool for a better detection of certain signals in a given ambient noise condition.     

Classification of Risso's and Pacific white-sided dolphins using spectral properties of echolocation clicks

The spectral and temporal properties of echolocation clicks and the use of clicks for species classification are investigated for five species of free-ranging dolphins found offshore of southern California: short-beaked common (Delphinus delphis), long-beaked common (D. capensis), Risso's (Grampus griseus), Pacific white-sided (Lagenorhynchus obliquidens), and bottlenose (Tursiops truncatus) dolphins. Spectral properties are compared among the five species and unique spectral peak and notch patterns are described for two species. The spectral peak mean values from Pacific white-sided dolphin clicks are 22.2, 26.6, 33.7, and 37.3 kHz and from Risso's dolphins are 22.4, 25.5, 30.5, and 38.8 kHz. The spectral notch mean values from Pacific white-sided dolphin clicks are 19.0, 24.5, and 29.7 kHz and from Risso's dolphins are 19.6, 27.7, and 35.9 kHz. Analysis of variance analyses indicate that spectral peaks and notches within the frequency band 24-35 kHz are distinct between the two species and exhibit low variation within each species. Post hoc tests divide Pacific white-sided dolphin recordings into two distinct subsets containing different click types, which are hypothesized to represent the different populations that occur within the region. Bottlenose and common dolphin clicks do not show consistent patterns of spectral peaks or notches within the frequency band examined (1-100 kHz).     

Single-lobed frequency-dependent beam shape in an echolocating false killer whale (Pseudorca crassidens)

Recent studies indicate some odontocetes may produce echolocation beams with a dual-lobed vertical structure. The shape of the odontocete echolocation beam was further investigated in a false killer whale performing an echolocation discrimination task. Clicks were recorded with an array of 16 hydrophones and frequency-dependent amplitude plots were constructed to assess beam shape. The majority of the echolocation clicks were single-lobed in structure with most energy located between 20 and 80 kHz. These data indicate the false killer whale does not produce a dual-lobed structure, as has been shown in bottlenose dolphins, which may be a function of lowered frequencies in the emitted signal due to hearing loss.     

Estimated transmission beam pattern of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris)

Recordings were made from white-beaked dolphins in Icelandic waters using a four-hydrophone array in a star configuration. The acoustic signals were amplified and sampled to a hard disk at a rate of 800 kHz per channel. The 3 and 10 dB beamwidths were calculated to be 8 degrees and 10 degrees, respectively, indicating a narrower transmission beam for white-beaked dolphins than that reported for bottlenose dolphins (Tursiops truncatus). The beamwidth was more similar to that found for belugas (Delphinapterus lucas). The measured beam pattern included large side lobes, perhaps due to the inclusion of off-axis clicks, even after applying several criteria to select only on-axis clicks. The directivity index was calculated to be 18 dB when using all data for angles from 0 degrees-50 degrees. The calculated sound radiation from a circular piston with a radius of 6 cm driven by a white-beaked dolphin click had a beam pattern very similar to the measured beam pattern for the main transmission lobe of the white-beaked dolphin. The directivity index was 29 dB. This is the first attempt to estimate the directionality index of dolphins in the field.     

Classification of echolocation clicks from odontocetes in the Southern California Bight

This study presents a system for classifying echolocation clicks of six species of odontocetes in the Southern California Bight: Visually confirmed bottlenose dolphins, short- and long-beaked common dolphins, Pacific white-sided dolphins, Risso's dolphins, and presumed Cuvier's beaked whales. Echolocation clicks are represented by cepstral feature vectors that are classified by Gaussian mixture models. A randomized cross-validation experiment is designed to provide conditions similar to those found in a field-deployed system. To prevent matched conditions from inappropriately lowering the error rate, echolocation clicks associated with a single sighting are never split across the training and test data. Sightings are randomly permuted before assignment to folds in the experiment. This allows different combinations of the training and test data to be used while keeping data from each sighting entirely in the training or test set. The system achieves a mean error rate of 22% across 100 randomized three-fold cross-validation experiments. Four of the six species had mean error rates lower than the overall mean, with the presumed Cuvier's beaked whale clicks showing the best performance (<2% error rate). Long-beaked common and bottlenose dolphins proved the most difficult to classify, with mean error rates of 53% and 68%, respectively.