Unmanned localization of sperm whales in realistic scenarios

In this paper an unmanned sperm whale localization technique is presented. It focuses on the localization of sperm whales using a two-hydrophone array passive localization system. It is based on the beamforming technique and on the time delay between the direct and surface reflected wavefronts. The proposed method is based on that presented by E. K. Skarsoulis [1] and it aims to develop a low computational complexity signal processing system, which can operate autonomously in remote buoys with power and computational limitations. This study consists on the analysis of the improvements provided by using beamforming theory on the method proposed in [1]. The eqnipment used mainly composed of two hydrophone arrays deployed near the surface. It was found that the accuracy of this methodology depends on the array's location and can be improved by increasing the depth and the separation between the arrays and/or decreasing the angle formed by the line which crosses through the arrays with respect to the horizontal plane. The performance of the proposed method is evaluated through simulations using a real sperm whale signal in deep water, in presence of low and high SNR. The enhancements are proven in the extraction of the direct and surface-reflection arrival times as well as the arrival angle for each path under realistic conditions.The authors would like to thanks the Instituto Superior the Engenharia of the University of Algarve, for receiving the first author under an European Union ERASMUS grant when this work was carried. This work is funded by the FCT project PHITOM [PTDCIEEA-TEU71263/2006]

Passive acoustic localization of sperm whales to facilitate ship strike avoidance

Ship strikes are one of the leading causes of premature mortality among whales, accounting for the deaths of approximately 20,000 each year, with untold more being injured. Given the exponential increase in shipping traffic, estimated at 2 - 3% year-over-year, the potential for collisions continues to grow. Due to their large size, preferred habitats and sea surface behavior, the sperm whale is one of the species most vulnerable to ship strikes. In some populations, collisions with maritime vessels are the leading cause of death, premature or otherwise. This is particularly concerning considering that the sperm whale is listed on the IUCN Red List of Threatened Species as “Vulnerable” globally and “Endangered” in the Mediterranean region. Passive Acoustic Monitoring, or PAM, is an environmentally non-intrusive method by which naturally generated underwater sounds, such as the clicks made by sperm whales, are picked up by hydrophones (underwater recording devices) and analyzed to extract a variety of data, including the sound source’s location. In the current research, we use a PAM methodology known as Time Difference of Arrival (TDOA) analysis, whereby different acoustic paths taken by sound waves from their source to a hydrophone are analyzed to extract the differences in time between their arrivals. Extracted TDOAs are compared to a theoretical model (in our case, the Bellhop ray tracing model) to extrapolate the source’s localization, which can then be fed into a live marine traffic system such as MarineTraffic (marinetraffic.com) to alert ships in the area to the presence and locations of the whales, so that they may take preventative action. In this dissertation, I present, inter alia, a working prototype, developed on the Matlab platform, for the detection and localization of sperm whales based on their vocalizations (clicks).As colisões com navios são uma das principais causas de mortalidade prematura entre as baleias, sendo responsáveis pela morte de aproximadamente 20.000 baleias a cada ano, com um número incontável de feridos. Os números exatos são difíceis de determinar porque as baleias feridas frequentemente saem para o mar, onde morrem e depois afundam no fundo do mar, não sendo mais avistadas. Em casos raros, baleias feridas podem encalhar, como aconteceu na costa de Almada, Portugal, em abril de 2022, quando um cachalote com lacerações visíveis – acredita-se ter sido causado por emaranhamento nos rotores de um navio – deu à costa e posteriormente morreu. Se há algum valor redentor para esses encalhes, é que eles fornecem aos cientistas uma pletora de informações inestimáveis sobre as causas e efeitos das colisões com navios. O cachalote é, sem dúvida, a espécie de cetáceo mais afetada por colisões com embarcações marítimas. Num estudo de 2018 de Díaz-Delgado et al., exames patológicos de 224 cetáceos encalhados, compreendendo 21 espécies diferentes, revelaram que o cachalote é, de longe, a espécie mais afetada por colisões de navios, representando quase metade (11 de 24) de todos os animais necropsiados mortos dessa maneira. Em algumas populações de cachalotes, as colisões com embarcações marítimas são tão comuns que são a principal causa de morte, prematura ou não. É o caso da região das Ilhas Canárias, onde se estima que cerca de 60% das mortes de cachalotes sejam atribuídas a golpes de navios. Infelizmente, as colisões de navios com os cachalotes continuam a aumentar a uma taxa exponencial. Existem três razões identificáveis para isso: A primeira é um aumento exponencial correspondente no tráfego marítimo. O número total de navios mercantes em todo o mundo mais que duplicou nos 8 anos entre 2004 e 2012 e mais que triplicou entre 1992 e 2012. Em 2018, mais de 92.000 navios mercantes navegaram pelos mares, transportando cerca de 12 mil milhões de toneladas de carga, um aumento de 35% em apenas uma década. O segundo fator é o comportamento específico de forrageamento do cachalote. Os cachalotes passam até 22 horas por dia caçando presas, incluindo cefalópodes e raias do fundo do mar, em profundidades de, em média, 600 a 1.000 metros, mas foram observados a mais de 2.000 metros. Nessas profundidades, eles devem enfrentar pressões extremas (superiores a 100 atmosferas) e escuridão total durante suas expedições de forrageamento, que podem durar até uma hora de cada vez. Como a visão é inútil nessas condições, acredita-se que os cachalotes usem a ecolocalização para localizar suas presas, produzindo uma série de cliques extremamente potentes que podem atingir níveis sonoros de 230 dB re 1 μPa a 1 m, tornando-os o som de maior intensidade gerado por qualquer animal existente. Quando a baleia emerge (o que, como mamífero dotado de pulmões e não de guelras, eventualmente deve fazê-lo), está exausta de caçar, suster a respiração, suportar pressões extremas e gerar cliques intensos, e deve descansar na superfície do mar, geralmente por cerca de 10 minutos, antes de iniciar seu próximo mergulho. É durante esses períodos de descanso que os cachalotes ficam relativamente imóveis e, portanto, particularmente vulneráveis a colisões com navios. Por uma infeliz coincidência, em certas áreas do mundo, como as Ilhas Canárias e ao largo da costa sudoeste da península do Peloponeso e Creta, é diretamente nas rotas marítimas movimentadas que os cachalotes escolhem descansar, porque as características batimétricas que atraem cachalotes por suas excelentes oportunidades de forrageamento, como as beiras das plataformas continentais e desfiladeiros íngremes, se sobrepõem às principais rotas de navegação nessas regiões. Um terceiro fator que causa um aumento no número de choques entre navios e cetáceos é o aumento do ruído submarino antropogénico que, como o volume de transporte, cresceu exponencialmente e que tem um efeito profundo não apenas nos cachalotes, mas na fauna marinha em geral. Estima-se que entre 1950 e 2007, os níveis de ruído ambiente de baixa frequência (25 - 50 Hz) nos oceanos, causados principalmente pelo constante ronco de fundo dos motores dos navios, aumentaram a uma taxa de 3,3 dB por década, chegando a 91 dB re 1 μPa2/Hz em 2007, a mesma intensidade de um assobio de golfinho. Como os decibéis são calculados em escala logarítmica, isso equivale a duplicar a intensidade do ruído a cada 10 anos. Os efeitos do aumento da poluição sonora sobre cachalotes e outros cetáceos são múltiplos, incluindo permanente deficiência auditiva, dessensibilização comportamental aos perigos associados ao ruído do navio e interrupções na disponibilidade e distribuição de suas presas. Embora a questão das colisões entre navios e baleias tenha recebido atenção crescente nos últimos anos, muito mais precisa de ser feito para mitigar esta forma completamente desnecessária e trágica de mortalidade de cetáceos. No caso dos cachalotes, há urgência, uma vez que muitos populações de cachalotes nunca se recuperaram tão rapidamente quanto o esperado após a promulgação da moratória internacional sobre a baleação comercial em 1986. Hoje em dia, a população mundial de cachalotes gira em torno de 200.000, pouco mais do que nos anos imediatamente anteriores à moratória, e muito menos do que os estimados 2 a 3 milhões de cachalotes que percorriam os mares em 1700, pouco antes de a espécie ser alvo de caça intensiva no século 19 por seu espermacete, uma mistura de ésteres de cera e triglicerídeos secretados nos órgãos produtores de som do crânio que era altamente valioso para uso em perfumes e velas. Como resultado, o cachalote permanece na Lista Vermelha de Espécies Ameaçadas da IUCN como "Vulnerável" globalmente e “Em Perigo, com Tendência Populacional: Diminuindo” na região do Mediterrâneo A Monitorização Acústica Passiva, ou PAM, é um método pelo qual sons subaquáticos gerados naturalmente, como cliques de cachalotes, são captados por hidrofones (dispositivos de gravação subaquática) e analisados para extrair uma variedade de dados. A PAM está a tornar-se cada vez mais popular na monitorização de cetáceos em geral, e cachalotes em particular, devido à combinação única de propriedades acústicas do clique “usual” do cachalote – volume, impulsividade e ampla faixa de frequência – o que o torna particularmente adequado para uso em técnicas de PAM. A vantagem da PAM em relação à monitorização da fauna marinha é que ele não é intrusivo: os sistemas PAM não geram som próprio e não envolvem contato direto com os animais. No entanto, a PAM pode ser usada efetivamente em uma variedade de aplicações, incluindo a determinação da presença e da localização de fontes de vocalização. Na investigação atual, usamos um método conhecido como análise de diferença de tempo de chegada (TDOA), em que diferentes caminhos percorridos pelas ondas sonoras à medida que viajam entre a fonte e o hidrofone, como caminhos diretos e os refletidos na superfície, são analisados para extrair a diferença de tempo entre os tempos de chegada. Os TDOAs extraídos são então comparados a um modelo teórico (no nosso caso, o modelo de traçamento de raios Bellhop), para extrapolar informações de localização sobre a fonte, incluindo a sua profundidade, distância horizontal (alcance) do hidrofone e ângulo de azimute. O resultado final pretendido é a localização quase em tempo real de todos os cachalotes nas proximidades de uma série de hidrofones, que podem então ser incluídos num sistema de tráfego marítimo em tempo real, como o MarineTraffic (marinetraffic.com) para alertar os navios na área para a presença e a localização das baleias, para que possam tomar ações preventivas, como reencaminhamento, redução de velocidade e colocação de observadores humanos de mamíferos marinhos no convés. Nesta dissertação, apresento, entre outros, um protótipo de trabalho, desenvolvido na plataforma Matlab, para a deteção e localização de cachalotes com base nas suas vocalizações (cliques)

Underwater Localization in a Confined Space Using Acoustic Positioning and Machine Learning

Localization is a critical step in any navigation system. Through localization, the vehicle can estimate its position in the surrounding environment and plan how to reach its goal without any collision. This thesis focuses on underwater source localization, using sound signals for position estimation. We propose a novel underwater localization method based on machine learning techniques in which source position is directly estimated from collected acoustic data. The position of the sound source is estimated by training Random Forest (RF), Support Vector Machine (SVM), Feedforward Neural Network (FNN), and Convolutional Neural Network (CNN). To train these data-driven methods, data are collected inside a confined test tank with dimensions of 6m x 4.5m x 1.7m. The transmission unit, which includes Xilinx LX45 FPGA and transducer, generates acoustic signal. The receiver unit collects and prepares propagated sound signals and transmit them to a computer. It consists of 4 hydrophones, Red Pitay analog front-end board, and NI 9234 data acquisition board. We used MATLAB 2018 to extract pitch, Mel-Frequency Cepstrum Coefficients (MFCC), and spectrogram from the sound signals. These features are used by MATLAB Toolboxes to train RF, SVM, FNN, and CNN. Experimental results show that CNN archives 4% of Mean Absolute Percentage Error (MAPE) in the test tank. The finding of this research can pave the way for Autonomous Underwater Vehicle (AUV) and Remotely Operated Vehicle (ROV) navigation in underwater open spaces

Source location of narrow band signals in multipath environments, with application to marine mammals

Thesis (Ph.D.)--Boston UniversityPassive acoustic localization has benefited from many major developments and has become an increasingly important focus point in marine mammal research. Several challenges still remain. This work seeks to address several of these challenges such as tracking the calling depths of baleen whales. In this work, data from an array of widely spaced Marine Acoustic Recording Units (MARUs) was used to achieve three dimensional localization by combining the methods Time Difference of Arrival (TDOA) and Direct-Reflected Time Difference of Anival (DRTD) along with a newly developed autocorrelation technique. TDOA was applied to data for two dimensional (latitude and longitude) localization and depth was resolved using DRTD. Previously, DRTD had been limited to pulsed broadband signals, such as sperm whale or dolphin echolocation, where individual direct and reflected signals are separated in time. Due to the length of typical baleen whale vocalizations, individual multipath signal arrivals can overlap making time differences of arrival difficult to resolve. This problem can be solved using an autocorrelation, which can extract reflection information from overlapping signals. To establish this technique, a derivation was made to model the autocorrelation of a direct signal and its overlapping reflection. The model was exploited to derive performance limits allowing for prediction of the minimum resolvable direct-reflected time difference for a known signal type. The dependence on signal parameters (sweep rate, call duration) was also investigated. The model was then verified using both recorded and simulated data from two analysis cases for North Atlantic right whales (NARWs, Eubalaena glacialis) and humpback whales (Megaptera noveaengliae). The newly developed autocorrelation technique was then combined with DRTD and tested using data from playback transmissions to localize an acoustic transducer at a known depth and location. The combined DRTD-autocorrelation methods enabled calling depth and range estimations of a vocalizing NARW and humpback whale in two separate cases. The DRTD-autocorrelation method was then combined with TDOA to create a three dimensional track of a NARW in the Stellwagen Bank National Marine Sanctuary. Results from these experiments illustrated the potential of the combined methods to successfully resolve baleen calling depths in three dimensions

Implementation of a Passive Acoustic Barrier for Surveillance

Dias, A. R., Santos, N. P., & Lobo, V. (2023). Implementation of a Passive Acoustic Barrier for Surveillance. In OCEANS 2023 - Limerick (pp. 1-6). IEEE Computer Society. https://doi.org/10.1109/OCEANSLimerick52467.2023.10244682With the end of the cold war, the interest in underwater warfare decreased dramatically. However, recent developments have brought underwater warfare back to center stage. Anti-submarine warfare is always one of the major concerns of a navy since it is difficult to detect an enemy submarine in the vast ocean. Conjugating the recent developments in unmanned vehicles and active and passive acoustic surveillance, we can perform better data fusion and increase our knowledge about the events occurring in our waters. The processed data originating from acoustic surveillance can potentially be an essential source of naval intelligence. An acoustic barrier can perform this detection with success. Still, these systems require highly qualified personnel to operate, present a costly infrastructure, and are hard to implement and maintain. Data fusion from multiple sources, and even from low-cost sensors with noisy measures, are a promising solution, especially if resource optimization is a priority. The implementation described in this paper is intended to be proof of concept of a low-cost implementation in shallow waters that can be easily expanded and evolved to different scenarios. The preliminary results obtained confirm that this is a viable solution.authorsversionpublishe

Relating behavioral context to acoustic parameters of bottlenose dolphin (Tursiops truncatus) vocalizations

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 2001This thesis presents methods to analyze the function of vocalizations of the bottlenose dolphin, Tursiops truncatus. The thesis uses the social interaction as the basic unit of analysis, and maintains a deliberate focus on quantitative and replicable analyses throughout. A method for determining identity of the vocalizing animal in a lagoon was developed. This method combined passive acoustic localization with video sampling to determine which animal vocalized. It fills an urgent need for unbiased identification of vocalizations of undisturbed dolphins where details of social interactions can be followed without affecting the behavior of the subjects. This method was implemented in a captive lagoon with 6 dolphins: two adult females, their two male calves, and a juvenile male and a juvenile female. This thesis also reviews the current state of analysis of the bottlenose dolphin acoustic repertoire, highlighting the need for a detailed, quantitative, and consistent study of the entire vocal repertoire. It does not attempt to do a comprehensive repertoire study, but uses several new quantitative methods to parameterize vocalizations and relate these to behavior from dolphins. Vocalizations within the lagoon tended to occur around the time of onset of behaviors produced by the focal dolphin. A comparison of vocalizations during affiliative and agonistic interactions revealed that the association of group vocalizations with the behavior of a focal animal was related to agonistic but not affiliative interactions. Using the localization/video method, vocalizations in a time window around submissive behaviors were localized and classified as having come from either dolphins engaged in the interaction or dolphins not engaged in the interaction. Vocalizations were emitted by interactants more often than expected, and by non-interactants less often than expected. Use of different vocalization types was found to vary depending on the context of the agonistic interaction. In addition, the sequence of vocalizations with respect to behaviors within the interaction mattered, with more vocalizations occurring after than before submissive behaviors. These results demonstrated that group-based analyses of vocalizations are insufficient and one must use techniques designed to focus on the level of the interaction in order to study communication and social behavior in dolphins.Funding was provided by the Waikoloa Marine Life fund, Grant No. IBN-9975523 from the National Science Foundation, a graduate student fellowship for R. Thomas from the National Science Foundation, and an Ocean Ventures Fund Grant for R. Thomas from the Woods Hole Oceanographic Institution

South China Sea internal tide/internal waves-impact on the temporal variability of horizontal array gain at 276 Hz

Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1292-1307, doi:10.1109/JOE.2004.836794.The temporal variability of the spatial coherence of an acoustic signal received on a bottomed horizontal array has been calculated for 276-Hz narrow-band signals. A conventional plane wave beamformer was applied to the received signals. The temporal variability of the array's omnipower, beam power, and array gain are related to variability in the sound-speed field. The spectral characteristics of array omnipower are nonstationary and changed as the spectral characteristics of the temperature field varied. The array omnipower and beam-power variability tracked each other in time and varied by as much as 15 dB over time intervals as short as 7 min. Array gain varied up to 5 dB and usually tracked the omnipower variability. A contiguous 24-h section of data is discussed in detail. This data section is from a time period during which the high-frequency fluid dynamic perturbation of the sound-speed field was of smaller amplitude than other sections of the 16-d data set. Consequently, this section of data sets an upper bound for the realizable array gain. The temporal variability of array gain and spatial coherence at times appears to be correlated with environmental perturbation of the sound-speed field, but are also correlated with changes in the signal-to-noise ratio. The data was acquired during the Office of Naval Research's South China Sea Asian Seas International Acoustics Experiment. The 465-m 32-channel horizontal array was placed on the bottom in 120 m of water at the South China Sea shelf break. The acoustic source was moored in 114 m of water /spl sim/19 km from the receiving array.This work was supported by the Office of Naval Research