The effect of recording and analysis bandwidth on acoustic identification of delphinid species

Because many cetacean species produce characteristic calls that propagate well under water, acoustic techniques can be used to detect and identify them. The ability to identify cetaceans to species using acoustic methods varies and may be affected by recording and analysis bandwidth. To examine the effect of bandwidth on species identification, whistles were recorded from four delphinid species (Delphinus delphis, Stenella attenuata, S. coeruleoalba, and S. longirostris) in the eastern tropical Pacific ocean. Four spectrograms, each with a different upper frequency limit (20, 24, 30, and 40 kHz), were created for each whistle (n = 484). Eight variables (beginning, ending, minimum, and maximum frequency; duration; number of inflection points; number of steps; and presence/absence of harmonics) were measured from the fundamental frequency of each whistle. The whistle repertoires of all four species contained fundamental frequencies extending above 20 kHz. Overall correct classification using discriminant function analysis ranged from 30% for the 20-kHz upper frequency limit data to 37% for the 40-kHz upper frequency limit data. For the four species included in this study, an upper bandwidth limit of at least 24 kHz is required for an accurate representation of fundamental whistle contours.     

Whistles of boto, Inia geoffrensis, and tucuxi, Sotalia fluviatilis

Whistles were recorded and analyzed from free-ranging single or mixed species groups of boto and tucuxi in the Peruvian Amazon, with sonograms presented. Analysis revealed whistles recorded falling into two discrete groups: a low-frequency group with maximum frequency below 5 kHz, and a high-frequency group with maximum frequencies above 8 kHz and usually above 10 kHz. Whistles in the two groups differed significantly in all five measured variables (beginning frequency, end frequency, minimum frequency, maximum frequency, and duration). Comparisons with published details of whistles by other platanistoid river dolphins and by oceanic dolphins suggest that the low-frequency whistles were produced by boto, the high-frequency whistles by tucuxi. Tape recordings obtained on three occasions when only one species was present tentatively support this conclusion, but it is emphasized that this is based on few data.     

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。      

基于子频带能量特征提取的汽车鸣笛声识别*

针对城市中汽车违法鸣笛声之间识别分类较难的问题，为了快速准确的识别鸣笛声并将不同种鸣笛声之间进行分类，在鸣笛声识别分类中提出了应用子频带能量提取鸣笛声的特征，并利用BP神经网络对提取的子频带能量特征值矩阵进行学习训练，且在神经网络学习过程中利用可变学习速度的方法，减小了神经网络的迭代次数。实验表明利用此种子频带能量特征提取法使鸣笛声与非鸣笛声的平均识别率达到了94.889%；使不同鸣笛声之间的分类正确率最大达到了93.75%，实现了不同鸣笛声之间的分类。     

Performance of a contour-based classification method for whistles of Mediterranean delphinids

Whistles from five delphinid species in the western Mediterranean Sea (Stenella coeruleoalba, Grampus griseus, Delphinus delphis, Tursiops truncatus, Globicephala melas) were taken from GREC sound archives. FFT contours (window size 512, Hanning, sampling frequency 44.1 kHz) were extracted with custom developed Matlab software: 277 samples of striped dolphins (Sc), 158 whistles of Risso’s dolphins (Gg), 120 of common dolphins (Dd), 76 of bottlenose dolphins (Tt), and 66 of pilot whales (Gm) were selected. Seafox software extracted 15 variables from the digitized contours, including: duration, initial, final, maximal and minimal frequency slopes, frequency range, number of frequency extrema, beginning, ending, maximal and minimal frequencies, presence of harmonics. Four of five species were significantly different (Mann-Whitney test) for average durations (respectively 0.73, 0.65, 0.47 and 0.89 s for Sc, Gg, Dd, Gm) while the average duration of bottlenose dolphins was 0.71 s. Frequency ranges (respectively 7.3, 6.3, 4.6, 3.2 and 6.3 kHz) were significantly different for all species pairs, with the exception of bottlenose and Risso’s dolphins. From a global point of view, pilot whale calls were the most distinct, with 43 significant pair-wise tests out of a total of 52, followed by the common dolphins. Risso’s dolphins were closest to other species whistles. A CART classification method achieved a global classification rate of 62.9%.     

Who is whistling? Localizing and identifying phonating dolphins in captivity

Acoustic communication through whistles is well developed in dolphins. However, little is known on how dolphins are using whistles because localizing the sound source is not an easy task. In the present study, the hyperbola method was used to localize the sound source using a two-hydrophone array. A combined visual and acoustic method was used to determine the identity of the whistling dolphin. In an aquarium in Mexico City where two adult bottlenose dolphins were housed we recorded 946 whistles during 22 days. We found that a dolphin was located along the calculated hyperbola for 72.9% of the whistles, but only for 60.3% of the whistles could we determine the identity of the whistling dolphin. However, sometimes it was possible to use other cues to identify the whistling dolphin. It could be the animal that performed a behavior named “observation” at the time whistling occurred or, when a whistle was only recorded on one channel, the whistling dolphin could be the animal located closest to the hydrophone that captured the whistle. Using these cues, 15.4% of the whistles were further ascribed to either dolphin to obtain an overall identification efficiency of 75.7%. Our results show that a very simple and inexpensive acoustic setup can lead to a reasonable number of identifications of the captive whistling dolphin: this is the first study to report such a high rate of whistles identified to the free swimming, captive dolphin that produced them. Therefore, we have a data set with which we can investigate how dolphins are using whistles. This method can be applied in other aquaria where a small number of dolphins is housed; though, the actual efficiency of this method will depend on how often dolphins spend time next to each other and on the reverberation conditions of the pool.     

Characteristics of whistles from rough-toothed dolphins (Steno bredanensis) in Rio de Janeiro coast, southeastern Brazil

There is no information about the whistles of rough-toothed dolphins in the South Atlantic Ocean. This study characterizes the whistle structure of free-ranging rough-toothed dolphins recorded on the Rio de Janeiro coast, southeastern Brazil, and compares it to that of the same species in other regions. A total of 340 whistles were analyzed. Constant (N = 115; 33.8%) and ascending (N = 99; 29.1%) whistles were the most common contours. The whistles recorded had their fundamental frequencies between 2.24 and 13.94 kHz. Whistles without inflection points were frequently emitted (N = 255; 75%). Some signals presented breaks or steps in their contour (N = 97; 28.5%). Whistle duration was short (347 ± 236 ms and 89.7% of the whistles lasted <600 ms). Seventy-eight whistle contour types were found in the total of whistles analyzed, and 27 (7.9%) of these occurred only once. Most of the whistle types were unique to a particular recording session (N = 43). The signals emitted by the rough-toothed dolphins in southeastern Brazil were characterized by low frequency modulation, short duration, low number of inflection points, and breaks. Differences in the mean values of the whistle parameters were found between this and other studies that recorded Steno bredanensis, but as in other localities, whistles above 14 kHz are rare.     

The broadband social acoustic signaling behavior of spinner and spotted dolphins

Efforts to study the social acoustic signaling behavior of delphinids have traditionally been restricted to audio-range (<20 kHz) analyses. To explore the occurrence of communication signals at ultrasonic frequencies, broadband recordings of whistles and burst pulses were obtained from two commonly studied species of delphinids, the Hawaiian spinner dolphin (Stenella longirostris) and the Atlantic spotted dolphin (Stenella frontalis). Signals were quantitatively analyzed to establish their full bandwidth, to identify distinguishing characteristics between each species, and to determine how often they occur beyond the range of human hearing. Fundamental whistle contours were found to extend beyond 20 kHz only rarely among spotted dolphins, but with some regularity in spinner dolphins. Harmonics were present in the majority of whistles and varied considerably in their number, occurrence, and amplitude. Many whistles had harmonics that extended past 50 kHz and some reached as high as 100 kHz. The relative amplitude of harmonics and the high hearing sensitivity of dolphins to equivalent frequencies suggest that harmonics are biologically relevant spectral features. The burst pulses of both species were found to be predominantly ultrasonic, often with little or no energy below 20 kHz. The findings presented reveal that the social signals produced by spinner and spotted dolphins span the full range of their hearing sensitivity, are spectrally quite varied, and in the case of burst pulses are probably produced more frequently than reported by audio-range analyses.     

Whistle variability in South Atlantic spinner dolphins from the Fernando de Noronha archipelago off Brazil

A series of quali- and quantitative analyses were conducted to evaluate the variability of spinner dolphin whistles from the Fernando de Noronha Archipelago off Brazil. Nine variables were extracted from each whistle contour, and the whistle contours shapes were classified into the seven categories described in Driscoll (1995). The analysis showed mean beginning and ending frequencies values of 10.78 and 12.74 kHz, respectively. On average, whistle duration was relatively short, with mean values around 0.495 s (N=702). Comparative analyses were also conducted to investigate the relationship between the obtained results and those presented in previous studies. When comparing averages, the results of the study of Oswald et al.(2003) in the Tropical Eastern Pacific (TEP) presented less significant differences in relation to this study; only whistle duration differed significantly between both works. The results of multivariate classification tests also pointed TEP population as the closest related to the population studied here. The similarities between such disjunct populations might be attributed to a more recent isolation event (the closing of the Panama Isthmus) than the divergence that has driven North and South Atlantic populations apart.     

一种宽吻海豚通讯信号自动分类的方法

针对宽吻海豚通讯信号自动分类提出了一种基于句法模式识别的方法。该方法首先提取海豚通讯信号基频随时间变化的轨迹曲线,然后提取基频变化的基元序列。根据海豚通讯信号分类的标准,归纳出产生各类海豚通讯信号基频基元序列的文法。对未知类别的海豚通讯信号,提取其基频变化的基元序列,根据各类模式的文法对基元序列进行分类,进而实现海豚通讯信号的自动分类。实验结果显示本文方法的分类准确率达到了95%。本文方法预期为海豚生物学行为的声学研究提供一定的技术支持。      

The freshwater dolphin Inia geoffrensis geoffrensis produces high frequency whistles

Because whistles are most commonly associated with social delphinids, they have been largely overlooked, ignored, or presumed absent, in solitary freshwater dolphin species. Whistle production in the freshwater dolphin, the boto (Inia geoffrensis geoffrensis), has been controversial. Because of its sympatry with tucuxi dolphins (Sotalia fluviatilis), a whistling species, some presume tucuxi whistles might have been erroneously assigned to the boto. Using a broadband recording system, we recorded over 100 whistles from boto dolphins in the Yasunf River, Ecuador, where the tucuxi dolphins are absent. Our results therefore provide conclusive evidence for whistle production in Inia geoffrensis geoffrensis. Furthermore, boto whistles are significantly different from tucuxi whistles recorded in nearby rivers. The Ecuadorian boto whistle has a significantly greater frequency range (5.30-48.10 kHz) than previously reported in other populations (Peru and Colombia) that were recorded with more bandwidth limited equipment. In addition, the top frequency and the range are greater than in any other toothed whale species recorded to date. Whistle production was higher during resting activities, alone or in the presence of other animals. The confirmation of whistles in the boto has important implications for the evolution of whistles in Cetacea and their association with sociality.     

A method for classifying whistles of bottlenose dolphin(Tursiops truncates) based on syntactic pattern reorganization

A method based on syntactic pattern recognition was presented to automatically classify whistles of bottlenose dolphin.Dolphin whistles have typically been characterized in terms of their instantaneous frequency as a function of time,which is also known as "whistle contour".The frequency variation features of a whistle were extracted according to its contour.Then,the frequency variation features were used for learning grammatical patterns.A whistle was classified according to grammatical pattern of its frequency variation features.The experimental results showed that the classification accuracy of the proposed method was 95%.The method can provide technical support for acoustic study of dolphins' biological behavior.     

一种近红外光谱在线监测新方法及其在中药柱层析过程中的应用

近红外光谱(NIRS)广泛应用于生产过程分析与监测,常需事先建立定量校正或定性判别模型,并需在生产条件变化后调整模型,使用较复杂。本文从相异度和相似度两个对立互补的角度,提出自适应移动窗口标准差法和过程光谱相似度法,并以此为基础建立一种针对生产过程的无需校正模型的简易光谱在线监测方法。论文以中药柱层析过程为例,对监测过程作NIRS自适应移动窗口标准差趋势图和过程光谱相似度趋势图,并通过HPLC离线分析所得的多指标成分含量变化趋势图进行对比验证,发现可用于工艺状况实时监测,指导收集起点、终点、溶液相变点的判断,表明论文提出的方法合理可行。该方法亦可用于紫外/可见、红外、拉曼、荧光等光谱及色谱、质谱等其他过程分析技术。     

光谱谐波分析的新型HAC非监督分类器

高光谱影像分类是识别影像信息的重要途径之一,研究其算法对地物识别、动态变化监测和专题信息提取等方面具有重要意义。非监督分类由于其具有无须先验知识的特点,被广泛应用于高光谱影像分类。结合谐波分析理论提出一种新的高光谱影像非监督分类算法,即谐波分析分类器(harmonic analysis classifier,HAC)。首先,该算法统计第一谐波分量并绘制其直方图,根据波峰数目及位置确定初始地物类别和聚类中心像元。然后将待分类像元光谱的波形信息映射到谐波分解次数、振幅和相位的特征空间中,利用同类地物在特征空间中表现聚集性这一特征,根据最小距离原则对待分类像元进行归类。最后,计算聚类中心像元间的欧式距离,通过设置距离阈值完成类间合并,从而达到高光谱影像分类的目的。提取两种地物类别的光谱曲线,经谐波分析后得到谐波分解次数、振幅和相位量,并分析其在特征空间中的分布情况验证了HAC算法的正确性。同时将HAC算法应用到EO-1卫星的Hyperion高光谱影像得到其分类结果,通过对比K-MEANS,ISODATA和HAC算法的高光谱影像分类结果,证实HAC算法作为一种非监督分类方法在高光谱影像分类方面具有较好的应用性。     

中药丹参及其近缘种中微量元素的主成分和聚类分析

采用原子吸收光谱法测定了不同产地的中药丹参及其近缘种植物白花丹参、雪山鼠尾草、云南鼠尾草、甘西鼠尾草、贵州鼠尾草、血盆草、粘毛鼠尾草、峨眉鼠尾草、黄鼠狼花、短唇鼠尾草和犬形鼠尾草中的Cu,Zn,Fe,Mg,Ca,Cr,Pb,Mo,Mn和Cd共10种微量元素的含量,应用主成分和聚类分析法对测定结果进行了研究。经过主成分分析得出3个主因子,其累计方差贡献率达79.3%。第一主因子的方差贡献率为49.6%,故所对应的Fe,Mn,Cu,Zn,Cd和Pb是丹参及其近缘种的特征元素。聚类分析将21个样品聚成2组,除浙江栽培丹参和白花丹参外,来自不同产地的9个丹参样品聚为一组;除贵州鼠尾草外,其他鼠尾草样品聚在一起,故此法可以将丹参和鼠尾草属其他植物区分开,总符合率达90%。因此利用原子吸收光谱法测定丹参及其近缘种中微量元素含量并对测定结果进行聚类分析是鉴别正品丹参的一种快速、准确的方法。     

Characteristics of whistles from the acoustic repertoire of resident killer whales (Orcinus orca) off Vancouver Island, British Columbia

The acoustic repertoire of killer whales (Orcinus orca) consists of pulsed calls and tonal sounds, called whistles. Although previous studies gave information on whistle parameters, no study has presented a detailed quantitative characterization of whistles from wild killer whales. Thus an interpretation of possible functions of whistles in killer whale underwater communication has been impossible so far. In this study acoustic parameters of whistles from groups of individually known killer whales were measured. Observations in the field indicate that whistles are close-range signals. The majority of whistles (90%) were tones with several harmonics with the main energy concentrated in the fundamental. The remainder were tones with enhanced second or higher harmonics and tones without harmonics. Whistles had an average bandwidth of 4.5 kHz, an average dominant frequency of 8.3 kHz, and an average duration of 1.8 s. The number of frequency modulations per whistle ranged between 0 and 71. The study indicates that whistles in wild killer whales serve a different function than whistles of other delphinids. Their structure makes whistles of killer whales suitable to function as close-range motivational sounds.     

Source levels and harmonic content of whistles in white-beaked dolphins (Lagenorhynchus albirostris)

Recordings of white-beaked dolphin whistles were made in Faxafl6i Bay (Iceland) using a three-hydrophone towed linear array. Signals from the hydrophones were routed through an amplifier to a lunch box computer on board the boat and digitized using a sample rate of 125 kHz per channel. Using this method more than 5000 whistles were recorded. All recordings were made in sea states 0-1 (Beaufort scale). Dolphins were located in a 2D horizontal plane by using the difference of arrival time to the three hydrophones, and source levels were estimated from these positions using two different methods (I and II). Forty-three whistles gave a reliable location for the vocalizing dolphin when using method II and of these 12 when using method I. Source level estimates on the center hydrophone were higher using method I [average source level 148 (rms) +/- 12 dB, n = 36] than for method II [average source level 139 (rms) +/- 12 dB, n = 36]. Using these rms values the maximum possible communication range for whistling dolphins given the local ambient noise conditions was then estimated. The maximum range was 10.5 km for a dolphin whistle with the highest source level (167 dB) and about 140 m for a whistle with the lowest source level (118 dB). Only two of the 43 whistles contained an unequal number of harmonics recorded at the three hydrophones judging from the spectrograms. Such signals could be used to calculate the directionality of whistles, but more recordings are necessary to describe the directionality of white-beaked dolphin whistles.     

High-pitched tonal signals of beluga whales (Delphinapterus leucas) in a summer assemblage off Solovetskii Island in the White Sea

High-frequency whistles of beluga whales are analyzed. The signals are recorded in a belgua summer assemblage off Solovetskii Island in the White Sea. The high-frequency whistles are narrowband signals with a continuous waveform and a fundamental frequency above 5 kHz. On the average, they make up 7.7% of the total vocal production of the animals. Based on the shape of the fundamental frequency contour and its time-frequency parameters, the high-frequency whistles are classed into 12 types. The HF whistles have a mean fundamental frequency of 9.7 kHz, an average bandwidth of 3.3 kHz, and an average duration of 1.0 s. The number of inflection points per signal ranges from 0 to 56 with a mean of 2.3. The predominant types are flat (50%), rising (23%), and wavy (7%) high-frequency whistles. Presumably, beluga whales can use some of the whistle types for short-range communication and other types for long-range communication. Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 2, pp. 156–164. The article was translated by the authors.