Advances in Sonar Technology

The demand to explore the largest and also one of the richest parts of our planet, the advances in signal processing promoted by an exponential growth in computation power and a thorough study of sound propagation in the underwater realm, have lead to remarkable advances in sonar technology in the last years.The work on hand is a sum of knowledge of several authors who contributed in various aspects of sonar technology. This book intends to give a broad overview of the advances in sonar technology of the last years that resulted from the research effort of the authors in both sonar systems and their applications. It is intended for scientist and engineers from a variety of backgrounds and even those that never had contact with sonar technology before will find an easy introduction with the topics and principles exposed here

Multi-regional acoustic repertoires of bottlenose dolphins : commom themes, geographical variatons and ecological factors

Thesis presented in fulfilment for the degree of PhD in Behavioural Biology presented at ISPA - Instituto UniversitárioOs golfinhos-roazes (Tursiops truncatus) são conhecidos por produzirem uma multiplicidade de sons, tanto para comunicação como para ecolocalização. O seu repertório acústico inclui sinais tonais com modulação de frequência – assobios, emissões curtas, de banda-larga e alta-frequência, os cliques de ecolocalização, e “pacotes” de pulsos de bandalarga e elevada taxa de repetição – sons pulsados. Esta tese centra-se no repertório acústico alargado da espécie T. truncatus e disponibiliza descrições detalhadas dos temas comuns, tanto a uma escala local com a uma escala geográfica alargada. Através de um estudo comparativo multi-regional, as (dis)similaridades no repertório foram avaliadas e as variações acústicas foram documentadas para nove populações de golfinhos-roazes do oceano Atlântico e do mar Mediterrâneo. A ocorrência de vocalizações universais em populações geograficamente distantes, mas também a variabilidade intraespecífica observada em grupos simpátricos que apresentam diferentes características eco-etológicas, sublinha a importância de fatores ambientais na modelação das emissões acústicas destes golfinhos. Ao estudar a estabilidade a longo-termo de assobios estereotipados, e a produção abundante de assobios não estereotipados em contextos alimentares específicos, foi possível corroborar o papel dos assobios como sinais de identidade. De modo a contribuir para um melhor entendimento acerca dos diferentes tipos de sinais que são usualmente nomeados como “Sons pulsados”, uma combinação de representações gráficas – sonogramas e dados quantitativos são aqui apresentados. Esta abordagem revelou que “rangidos”, “chorincos” e “buzzes”, vulgarmente agrupados em estudos de repertórios acústicos, são sinais acústicos distintos com diferenças significativas ao nível das suas características temporais e de frequência. Sequências rítmicas são também uma componente importante do repertório acústico dos golfinhos. Neste estudo, os zurros gravados no estuário do Sado, em Portugal, foram utilizados como base para a caracterização estrutural dos diferentes elementos acústicos que compõem estas sequências repetitivas, e técnicas de teoria da informação foram aplicadas para analisar a ordem dos elementos e a complexidade das sequências. Características-chave dos zurros mostram que estas vocalizações são emitidas de modo não-aleatório, o que sugere a presença de conteúdo informativo relevante, uma nova perspectiva sobre estas emissões acústicas mal conhecidas. Finalmente, a influência do tráfego marítimo, especialmente o ruído gerado pelos navios, nos repertórios acústicos de golfinhos-roazes não deve ser subvalorizado, uma vez que as embarcações contribuem marcadamente para a paisagem acústica subaquática atual. Decréscimos significativos nas taxas de emissão e alterações temporárias nas características espectrais dos assobios, aqui documentadas, revelam a existência de respostas acústicas à proximidade de embarcações, e adaptações locais a um ambiente mais ruidoso. Uma descrição enquadrada dos diferentes elementos vocais que fazem parte do repertório acústico da espécie golfinho-roaz, bem como da influência de fatores ecológicos, nomeadamente o ruído produzido por embarcações, aqui apresentados, pretendem ser contributos substanciais para o conhecimento do sistema de comunicação acústica desta espécie que deveriam ser utilizados em esforços de conservação.Os golfinhos-roazes (Tursiops truncatus) são conhecidos por produzirem uma multiplicidade de sons, tanto para comunicação como para ecolocalização. O seu repertório acústico inclui sinais tonais com modulação de frequência – assobios, emissões curtas, de banda-larga e alta-frequência, os cliques de ecolocalização, e “pacotes” de pulsos de bandalarga e elevada taxa de repetição – sons pulsados. Esta tese centra-se no repertório acústico alargado da espécie T. truncatus e disponibiliza descrições detalhadas dos temas comuns, tanto a uma escala local com a uma escala geográfica alargada. Através de um estudo comparativo multi-regional, as (dis)similaridades no repertório foram avaliadas e as variações acústicas foram documentadas para nove populações de golfinhos-roazes do oceano Atlântico e do mar Mediterrâneo. A ocorrência de vocalizações universais em populações geograficamente distantes, mas também a variabilidade intraespecífica observada em grupos simpátricos que apresentam diferentes características eco-etológicas, sublinha a importância de fatores ambientais na modelação das emissões acústicas destes golfinhos. Ao estudar a estabilidade a longo-termo de assobios estereotipados, e a produção abundante de assobios não estereotipados em contextos alimentares específicos, foi possível corroborar o papel dos assobios como sinais de identidade. De modo a contribuir para um melhor entendimento acerca dos diferentes tipos de sinais que são usualmente nomeados como “Sons pulsados”, uma combinação de representações gráficas – sonogramas e dados quantitativos são aqui apresentados. Esta abordagem revelou que “rangidos”, “chorincos” e “buzzes”, vulgarmente agrupados em estudos de repertórios acústicos, são sinais acústicos distintos com diferenças significativas ao nível das suas características temporais e de frequência. Sequências rítmicas são também uma componente importante do repertório acústico dos golfinhos. Neste estudo, os zurros gravados no estuário do Sado, em Portugal, foram utilizados como base para a caracterização estrutural dos diferentes elementos acústicos que compõem estas sequências repetitivas, e técnicas de teoria da informação foram aplicadas para analisar a ordem dos elementos e a complexidade das sequências. Características-chave dos zurros mostram que estas vocalizações são emitidas de modo não-aleatório, o que sugere a presença de conteúdo informativo relevante, uma nova perspectiva sobre estas emissões acústicas mal conhecidas. Finalmente, a influência do tráfego marítimo, especialmente o ruído gerado pelos navios, nos repertórios acústicos de golfinhos-roazes não deve ser subvalorizado, uma vez que as embarcações contribuem marcadamente para a paisagem acústica subaquática atual. Decréscimos significativos nas taxas de emissão e alterações temporárias nas características espectrais dos assobios, aqui documentadas, revelam a existência de respostas acústicas à proximidade de embarcações, e adaptações locais a um ambiente mais ruidoso. Uma descrição enquadrada dos diferentes elementos vocais que fazem parte do repertório acústico da espécie golfinho-roaz, bem como da influência de fatores ecológicos, nomeadamente o ruído produzido por embarcações, aqui apresentados, pretendem ser contributos substanciais para o conhecimento do sistema de comunicação acústica desta espécie que deveriam ser utilizados em esforços de conservação.Fundação para a Ciência e Tecnologia - FC

Information-driven cooperative approaches for AUVs seabed surveying

This Thesis investigates innovative exploration methods for marine area search with teams of autonomous underwater vehicles (AUVs). In particular, methods for cooperative adaptive motion planning have been developed, general in nature, but in our case applied to the field of marine archaeological search, where the goal is to find remnants or objects resting on, or buried in, the seabed. The exploration and motion planning problem is divided in two main lines of investigation. The first consists in defining a map of a priori detection probability in accordance with the available information and data over the survey area. Therefore, a refined mathematical method, that uses Parzen windows theory with Gaussian kernels, is developed for building the a priori map. The Renyi's entropy is used as the metric indicating relative information gain. The second line of investigation instead defines how to compute the optimal waypoints for each AUV when the search mission is in progress. It can be seen as a classical problem of motion planning, which in marine environment usually involves preplanning paths offline before the exploration, either zig-zag or regular lawn-mower transects. The lawn-mower patterns have some failings: • The AUV may not be able to search in marine areas where the a priori probability is optimum. Hence, the AUV does not move in areas with higher density of objects resting on or buried in the seabed. • If during the mission some objects are discovered the pre-specified path does not change. Instead, these objects may have influence on a priori information used at the beginning of the mission and therefore a new planning path may be requested. • The map of a priori detection probability is not updated dynamically with the exploration in progress. • The AUVs are not able to establish a cooperative communication and localization procedure. Hence, once the vehicle submerges, its location estimate will drift, eventually deviating from the pre-specified paths. These failures are ridden out using a new online and adaptive approach to define the AUVs' paths. Therefore, a cooperative distributed algorithm is developed defining the AUVs' waypoints by the minimization of the information entropy over the a priori map. Note that the a-priori map built as previously indicated is naturally suited to this approach. The algorithm is implemented by partitioning the marine area through the Equitable Power Diagrams theory, by potential functions for motion planning and taking into account communication constraints. The benefits of the proposed algorithms are evaluated within the application field of underwater archaeology. In particular, a performance metric has been defined in terms of relicts found in a fixed time, time to complete the mission, number of relicts found and area explored for relicts found. The Tuscan Archipelago database, kindly made available to us by the Tuscan Superintendence on Cultural Heritage, has given the ground information to apply the investigated algorithms. Simulations results are summarized to show the effectiveness of the novel proposed exploration method. While the performance results are tied to the application domain chosen, it is clear that the methodology and approaches proposed can also be used for other search and rescue applications

Decision-Making for Search and Classification using Multiple Autonomous Vehicles over Large-Scale Domains

This dissertation focuses on real-time decision-making for large-scale domain search and object classification using Multiple Autonomous Vehicles (MAV). In recent years, MAV systems have attracted considerable attention and have been widely utilized. Of particular interest is their application to search and classification under limited sensory capabilities. Since search requires sensor mobility and classification requires a sensor to stay within the vicinity of an object, search and classification are two competing tasks. Therefore, there is a need to develop real-time sensor allocation decision-making strategies to guarantee task accomplishment. These decisions are especially crucial when the domain is much larger than the field-of-view of a sensor, or when the number of objects to be found and classified is much larger than that of available sensors. In this work, the search problem is formulated as a coverage control problem, which aims at collecting enough data at every point within the domain to construct an awareness map. The object classification problem seeks to satisfactorily categorize the property of each found object of interest. The decision-making strategies include both sensor allocation decisions and vehicle motion control. The awareness-, Bayesian-, and risk-based decision-making strategies are developed in sequence. The awareness-based approach is developed under a deterministic framework, while the latter two are developed under a probabilistic framework where uncertainty in sensor measurement is taken into account. The risk-based decision-making strategy also analyzes the effect of measurement cost. It is further extended to an integrated detection and estimation problem with applications in optimal sensor management. Simulation-based studies are performed to confirm the effectiveness of the proposed algorithms

Vocal Repertoire, Social Structure and Feeding Preferences of Australian and Antarctic Killer Whales (Orcinus orca)

This thesis aimed to improve the understanding of killer whale populations in the Australian and Antarctic regions. Visual surveys, photo-identification and passive acoustic recordings were combined to study these populations. This study describes the call repertoire of killer whales found in Australian and Antarctic waters, presents an acoustic comparison between sympatric ecotypes in Antarctic waters and investigates the sociality and feeding preferences of killer whales in the Bremer Sub-Basin

Advancement of methods for passive acoustic monitoring : a framework for the study of deep-diving cetacean

Marine mammals face numerous anthropogenic threats, including fisheries interactions, ocean noise, ship strikes, and marine debris. Monitoring the negative impact on marine mammals through the assessment of population trends requires information about population size, spatiotemporal distribution, population structure, and animal behavior. Passive acoustic monitoring has become a viable method for gathering long-term data on highly mobile and notoriously cryptic marine mammals. However, passive acoustic monitoring still faces major challenges requiring further development of robust analysis tools, especially as it becomes increasingly used in applied conservation for long-term and large-scale studies of endangered or data deficient species such as sperm or beaked whales. Further challenges lie in the translation of animal presence into quantitative population density estimates since methods must control for variation in acoustic detectability of the target species, environmental factors, and for species-specific vocalization rates. The main contribution of this thesis is the advancement of the framework for long-term quantitative monitoring of cetacean species, applied to deep-divers like sperm and beaked whales. Fully-automated methods were developed and implemented to different populations of beaked whales in different conditions. This provided insight into generalization capabilities of these automatic techniques and best practices. However, implementing these tool kits is not always practical, and alternative methods for additional data processing were developed to expeditiously serve multiple purposes including annotation of individual sounds, evaluation of data in order to provide a highly dynamic technique, and classification for quantitative monitoring studies. This work also presents the longest time series of sperm whale presence using passive acoustic monitoring for over seven years in the Gulf of Mexico. Echolocation clicks were detected and discriminated from other sounds to understand the spatiotemporal distribution and structure of the population. A series of steps were implemented to provide adequate parameters and characteristics of the target population for density estimation using an echolocation click-based method. This allowed for the study of the Gulf of Mexico’s sperm whale population, providing significant progress towards the understanding of the population structure, distribution, and trends, in addition to potential long-term impacts of the well-known catastrophic Deepwater Horizon oil spill and other anthropogenic activities. The emergence of innovative approaches for detecting the presence of marine mammals and documenting human interactions can provide insight into ecosystem change. These species can be used as sentinels of ocean health to ensure the conservation of their marine environment into the next epoch.Els mamífers marins s'enfronten a nombroses amenaces antropogèniques, incloses les interaccions pesqueres, la contaminació acústica als oceans, les coalicions amb vaixells i els residus marins. El seguiment de l'impacte d’aquestes amenaces en els mamífers marins mitjançant l'avaluació de les tendències poblacionals requereix informació sobre la mida i l’estructura poblacional, la distribució espaciotemporal i el comportament dels animals. El seguiment amb sistemes d’acústica passiva s'ha convertit en un mètode viable per recollir dades a llarg termini de mamífers marins altament mòbils i críptics. Tanmateix, el seguiment acústic passiu encara ha d’afrontar reptes importants en el desenvolupament d'eines d'anàlisi robustes, especialment de cara al recent increment en el seu ús en la conservació aplicada a seguiments a llarg termini i a gran escala d'espècies en perill d'extinció o amb dades insuficients com ara el catxalot o els zífids. Altres reptes són traduir la presència d’animals a estimacions quantitatives de densitat poblacional, degut a que els mètodes han de controlar la variabilitat en la detecció acústica de les espècies en qüestió, els factors ambientals i les freqüències de vocalització específiques de cada espècie. La principal contribució d'aquesta tesi és l'avanç en els mètodes de seguiment quantitatiu a llarg termini de les espècies de cetacis, aplicat a espècies que viuen a grans profunditats com el catxalot i els zífids. Durant aquesta tesi, s’han desenvolupat i aplicat mètodes totalment automatitzats per detectar zífids de diferents poblacions i en diferents condicions. Aquests mètodes han proporcionat informació sobre la capacitat de generalització d'aquestes tècniques automàtiques i han permès fer recomanacions de bones pràctiques. Tanmateix, degut a que la implementació d’aquestes eines no és sempre pràctic, s’han desenvolupat mètodes per al processament de dades de forma expeditiva, que tenen diversos propòsits, que inclouen l’anotació de sons individuals, l’avaluació de dades per proporcionar una tècnica més dinàmica i la classificació per a estudis de seguiment quantitatiu. Aquest treball també presenta la sèrie temporal més llarga documentada de la presència de catxalots obtinguda mitjançant tècniques de seguiment acústic passiu durant més de set anys al Golf de Mèxic. S’han detectat i discriminat les senyals d'ecolocalització d'altres sons per tal de comprendre la distribució i l'estructura espaciotemporal d’aquesta població de catxalots. S’han implementat una sèrie de passos per proporcionar paràmetres i característiques de la població amb l’objectiu d'estimar la densitat mitjançant un mètode basat en senyals d’ecolocalització. Aquesta implementació ha permès l'estudi de la població de catxalots del Golf de Mèxic i ha suposat un progrés significatiu per la comprensió de l'estructura, la distribució i les tendències poblacionals, així com dels potencials impactes a llarg termini del catastròfic vessament de petroli de la plataforma Deepwater Horizon i altres activitats antropogèniques.Postprint (published version

Impacts of ship noise on the nighttime foraging behaviors of the North Atlantic humpback whale (Megaptera novaeangliae)

The humpback whale (Megaptera novaeangliae) is an endangered baleen whale species with a cosmopolitan distribution. The coastal habitat of this species result in significant exposure to anthropogenic noise from human activities. Previous research in the well-studied Pacific populations has demonstrated changes in calling behavior in response to noise, but noise impacts on other critical behaviors such as foraging have not yet been investigated. This study examines the impacts of ship noise on the nighttime bottom foraging behavior of humpback whales in the North Atlantic – a region with substantial human activity including high levels of noise from commercial shipping traffic. Data were collected from 2006 to 2009 in the Stellwagen Bank National Marine Sanctuary in the southern Gulf of Maine during June and July. Data included underwater behaviors and acoustic recordings of surrounding environmental noise collected using an archival tag attached to nine individual whales. Here I use series of linear mixed models to assess the effects of ship noise on eight metrics of nighttime feeding behaviors. Fixed effects included the presence versus absence of ship noise, received level of ship noise, and the before, during, or after ship noise exposure period. These variables had significant influence on three metrics: dive descent rate, ascent rate, and number of rolls indicative of feeding events. Descent rate decreased as noise level increased, while ascent rate was significantly faster in the during or after period when compared to the before period. The number of rolls significantly increased in the after exposure period, but at the greatest received levels, feeding rolls were completely absent during dives. These findings indicate that humpback whales on Stellwagen Bank show small, but significant, changes in foraging activity when exposed to ship noise. This study supports the hypothesis that environmental noise has an impact on the nighttime foraging activities of this species

Social calling behavior of Southeast Alaskan humpback whales (Megaptera novaeangliae) : classification and context

Humpback whales (Megaptera novaeangliae) are vocal baleen whales that exhibit complex social interactions that vary spatially and seasonally. Across their range, humpback whales produce a wide array of vocalizations including ‘song’, foraging vocalizations, and a range of vocalizations known as social calls -- unclassified non-song vocalizations. This study investigates the vocal repertoire and social calling behavior of Southeast Alaskan humpback whales from a sample of 299 vocalizations paired with 365 visual surveys collected over a three-month period on a foraging ground in Frederick Sound in Southeast Alaska. The results of this study describe a more varied and diverse repertoire of social vocalizations than has been previously documented, and identifies variability in vocal behavior as a function of social-spatial context. We used a three-part classification system that included aural-visual analysis, statistical cluster analyses, and discriminant function analysis to describe and classify social vocalizations. Vocalizations were classified into sixteen individual call types nested in seven vocal subclasses, within four vocal classes. The vocal repertoire of Southeast Alaskan humpbacks shows that call stereotypy ranges from discrete to continuous. This discrimination occurs at the vocal class and vocal subclass levels, and may be associated with call function. Social calls from Southeast Alaska showed anecdotal overlap with song from the 2012 North Pacific breeding season, and moderate overlap with vocalizations recorded in North Atlantic foraging grounds and along the East Australian migratory corridor. At the vocal class level aural-visual analysis had 83% agreement with cluster analysis and 90% agreement with discriminant function analysis. Results indicate that call use is not indiscriminant, and that some call types were commonly produced while others were rare. Moreover, calling rates in one vocal class, the pulsed (P) vocal class, were negatively correlated with mean nearest neighbor distance, indicating that P calling rates increased as animals clustered. This suggests the use of P calls may be spatially mediated. Results of a Poisson log linear (PLL) regression indicated that whale abundance in the survey area had no effect on vocal behavior; however, vocal behavior did vary significantly based on the spatial proximity of animals. The highest calling diversity occurred when whales were in clustered dispersion states, while the lowest calling diversity occurred when only a single whale was present. The type of calls produced during each dispersion state (clustered, random, evenly dispersed, single) varied significantly. While calls from all four vocal classes were detected during surveys containing clustered or randomly dispersed whales, calls from only two of the four classes were detected when whales were evenly distributed, and only one vocal class was detected from solitary whales. Our results indicated that vocal behavior is not correlated with abundance, that vocal behavior does vary based on social context, and that vocal behavior trends toward complexity as the potential for social interactions increases. Our evidence supports the hypothesis that social vocalizations serve a communicative purpose and may be used to maintain animal spatial proximity