165 research outputs found
Sea glider guidance around a circle using distance measurements to a drifting acoustic source
International audienceThis paper describes a simple yet robust sea glider guidance method in a constellation of Lagrangian drifters under the polar ice cap. The glider has to perform oceanographic measurements, mainly conductivity, temperature and depth, in the area enclosed by the drifters and can not rely on GNSS (Global Navigation Satellite System) positionning data as the polar ice cap makes it impossible to surface. The originality of the presented method resides in 2 points. First, a very simple PID (Proportional, Integral and Derivative) controller based on a basic kinematic model is tuned. Second, the method does not use a localization algorithm to estimate state space model data but interval analysis methods are performed to bound the errors in range to the transponder and its derivative. Moreover, only one acoustic beacon is used. Validation is then performed through simulations
Detections of whale vocalizations by simultaneously deployed bottom-moored and deep-water mobile autonomous hydrophones
Funding for this work was provided by the Living Marine Resources Program (N39430-14-C-1435 and N39430-14-C-1434), the Office of Naval Research (N00014-15-1-2142, N00014-10-1-0534, and N00014-13-1-0682), and NOAA’s Southwest Fisheries Science Center. SF was supported by the National Science and Engineering Graduate Fellowship.Advances in mobile autonomous platforms for oceanographic sensing, including gliders and deep-water profiling floats, have provided new opportunities for passive acoustic monitoring (PAM) of cetaceans. However, there are few direct comparisons of these mobile autonomous systems to more traditional methods, such as stationary bottom moored recorders. Cross-platform comparisons are necessary to enable interpretation of results across historical and contemporary surveys that use different recorder types, and to identify potential biases introduced by the platform. Understanding tradeoffs across recording platforms informs best practices for future cetacean monitoring efforts. This study directly compares the PAM capabilities of a glider (Seaglider) and a deep-water profiling float (QUEphone) to a stationary seafloor system (High-frequency Acoustic Recording Package, or HARP) deployed simultaneously over a 2 week period in the Catalina Basin, California, United States. Two HARPs were deployed 4 km apart while a glider and deep-water float surveyed within 20 km of the HARPs. Acoustic recordings were analyzed for the presence of multiple cetacean species, including beaked whales, delphinids, and minke whales. Variation in acoustic occurrence at 1-min (beaked whales only), hourly, and daily scales were examined. The number of minutes, hours, and days with beaked whale echolocation clicks were variable across recorders, likely due to differences in the noise floor of each recording system, the spatial distribution of the recorders, and the short detection radius of such a high-frequency, directional signal type. Delphinid whistles and clicks were prevalent across all recorders, and at levels that may have masked beaked whale vocalizations. The number and timing of hours and days with minke whale boing sounds were nearly identical across recorder types, as was expected given the relatively long propagation distance of boings. This comparison provides evidence that gliders and deep-water floats record cetaceans at similar detection rates to traditional stationary recorders at a single point. The spatiotemporal scale over which these single hydrophone systems record sounds is highly dependent on acoustic features of the sound source. Additionally, these mobile platforms provide improved spatial coverage which may be critical for species that produce calls that propagate only over short distances such as beaked whales.Publisher PDFPeer reviewe
RRS Discovery Cruise 381, 28 Aug - 03 Oct 2012. Ocean Surface Mixing, Ocean Submesoscale Interaction Study (OSMOSIS)
Cruise D381 was made in support of NERC's Ocean Surface Boundary Layer theme action programme, OSMOSIS (Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study). The ocean surface boundary layer (OSBL) deepens in response to convective, wind and surface wave forcing, which produce three-dimensional turbulence that entrains denser water, deepening the layer. The OSBL shoals in response to solar heating and to mesoscale and sub-mesoscale motions that adjust lateral buoyancy gradients into vertical stratification. Recent and ongoing work is revolutionising our view of both the deepening and shoaling processes: new processes are coming into focus that are not currently recognised in model parameterisation schemes. In OSMOSIS we have a project which integrates observations, modelling studies and parameterisation development to deliver a step change in modelling of the OSBL. The OSMOSIS overall aim is to develop new, physically based and observationally supported, parameterisations of processes that deepen and shoal the OSBL, and to implement and evaluate these parameterisations in a state-of-the-art global coupled climate model, facilitating improved weather and climate predictions. Cruise D381 was split into two legs D381A and a process study cruise D381B. D381A partly deployed the OSMOSIS mooring array and two gliders for long term observations near the Porcupine Abyssal Plain Observatory. D381B firstly completed mooring and glider deployment work begun during the preceding D381A cruise. D381B then carried out several days of targetted turbulence profiling looking at changes in turbulent energy dissipation resulting from the interation of upper ocean fluid structures such as eddies, sub-mesoscale filaments and Langmuir cells with surface wind and current shear. Finally D381B conducted two spatial surveys with the towed SeaSoar vehicle to map and diagnose the mesoscale and sub-mesoscale flows, which, unusually, are the `large scale' background in which this study sits
RRS Discovery Cruise 381, 28 Aug - 03 Oct 2012. Ocean Surface Mixing, Ocean Submesoscale Interaction Study (OSMOSIS)
Cruise D381 was made in support of NERC's Ocean Surface Boundary Layer theme action programme, OSMOSIS (Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study). The ocean surface boundary layer (OSBL) deepens in response to convective, wind and surface wave forcing, which produce three-dimensional turbulence that entrains denser water, deepening the layer. The OSBL shoals in response to solar heating and to mesoscale and sub-mesoscale motions that adjust lateral buoyancy gradients into vertical stratification. Recent and ongoing work is revolutionising our view of both the deepening and shoaling processes: new processes are coming into focus that are not currently recognised in model parameterisation schemes. In OSMOSIS we have a project which integrates observations, modelling studies and parameterisation development to deliver a step change in modelling of the OSBL. The OSMOSIS overall aim is to develop new, physically based and observationally supported, parameterisations of processes that deepen and shoal the OSBL, and to implement and evaluate these parameterisations in a state-of-the-art global coupled climate model, facilitating improved weather and climate predictions. Cruise D381 was split into two legs D381A and a process study cruise D381B. D381A partly deployed the OSMOSIS mooring array and two gliders for long term observations near the Porcupine Abyssal Plain Observatory. D381B firstly completed mooring and glider deployment work begun during the preceding D381A cruise. D381B then carried out several days of targetted turbulence profiling looking at changes in turbulent energy dissipation resulting from the interation of upper ocean fluid structures such as eddies, sub-mesoscale filaments and Langmuir cells with surface wind and current shear. Finally D381B conducted two spatial surveys with the towed SeaSoar vehicle to map and diagnose the mesoscale and sub-mesoscale flows, which, unusually, are the `large scale' background in which this study sits
Recommended from our members
Applications of slow-moving autonomous platforms for passive acoustic monitoring and density estimation of marine mammals
Advances in mobile autonomous vehicles for oceanographic sensing provide new opportunities for passive acoustic monitoring of marine mammals. Acoustically equipped mobile autonomous platforms, including gliders, deep-water profiling floats, and drifting surface buoys can survey for a variety of marine mammal species over intermediate spatiotemporal scales. Additionally, such mobile platforms may provide an effective tool for population density estimation of marine mammals. This dissertation advances our understanding of how gliders, deep-water floats, and surface drifters can be used for passive acoustic monitoring and density estimation of two cetacean species, fin whales (Balaenoptera physalus), and Cuvier’s beaked whales (Ziphius cavirostris).
One glider and two drifting deep-water floats were simultaneously deployed in the vicinity of a deep-water cabled hydrophone array offshore of San Clemente Island, California, USA. The glider was able to follow a pre-defined track while float movement was somewhat unpredictable. Fin whale 20 Hz pulses were recorded by all recorders throughout the two-week deployment and presence at hourly and daily scales were comparable across all recorders. Performance of an automated template detector did not differ by recorder type. However, the glider data contained up to 78% fewer fin whale detections per hour compared to the floats or stationary hydrophones because of increased low-frequency flow noise present during glider descents. Flow noise was related to glider speed through water and dive state. Glider speeds through water of 25 cm/s or less are suggested to minimize flow noise.
The cabled hydrophone array was also used to estimate fin whale localizations and tracks concurrently with the glider survey. These tracks were used in a trial-based approach to estimate a detection function for six-minute snapshots containing fin whale 20 Hz pulses. Detection probability was strongly dependent on 40 Hz noise levels (flow noise) recorded on the glider. At the median noise level of 97 kHz dB re 1 μPa2/Hz, maximum detection range was nearly 40 km and the estimated effective survey was 870 km2. Density of fin whales was estimated as 2.4 whales per 1000 km2 (coefficient of variation, CV 0.55) using a group size estimate from the tracked whales and an externally derived vocal rate from tagged fin whales. The framework presented here could be applied to other baleen whale species to advance the use of autonomous gliders for density estimation of cetacean species.
A second two-week glider and float deployment was conducted concurrently with the deployment of a commonly used deep-water stationary recorder, the High-frequency Acoustic Recording Package (HARP) and an array of drifting near-surface recorders in the Catalina Basin, California, USA. Acoustic recordings were analyzed for the presence of multiple marine mammal species, including beaked whales, delphinids, and minke whales and were compared across the glider, float, and HARPs. Detections of beaked whale echolocation clicks were variable across recorders, likely due to differences in the recording limits of each system, the spatial distribution of the recorders, and the short detection radius of such a high-frequency, directional signal type. Delphinid whistles and clicks were prevalent across all recorders, and at levels that may have masked beaked whale vocalizations. Minke whale (Balaenoptera acutorostrata) boing sounds were detected almost identically across all recorder types, as was expected given the relatively long detection range of the boing call type.
Spatially explicit capture-recapture was used to estimate density of Cuvier’s beaked whales from the near-surface drifting array of acoustic recorders. A snapshot approach was used with presence or absence of echolocation clicks within a 1-minute snapshot acting as the sampling unit. Using external estimates of group size and echolocation probability in a 1-minute snapshot, the density of Cuvier’s beaked whales, from the two best models was estimated at 5.48 animals per 1000 km2 (CV 0.46). This estimate was similar to estimates calculated using trial-based and distance sampling approaches applied to the same data set. Simulation experiments were conducted to investigate potential bias in estimated density caused by the configuration of the drifting array. Bias from the array configuration was found to be negligible, increased array spacing (approximately doubling and tripling between-sensor spacing) decreased bias, and the drifting aspect of the recorders also decreased bias, compared to simulations with stationary sensors.
This work provides evidence that animal presence and absence at broad spatial scales such as hours and days are comparable across gliders, deep-water floats, and stationary recorders. The spatial advantage of mobile instruments is most pronounced for species with short acoustic detection ranges, such as beaked whales. Marine mammal density can be estimated from gliders and mobile drifters using either a trial-based or SECR approach examples presented here provide an exciting advance in marine mammal population monitoring
Acoustic underwater target tracking methods using autonomous vehicles
Marine ecological research related to the increasing importance which the fisheries sector has reached so far, new methods and tools to study the biological components of our oceans are needed. The capacity to measure different population and environmental parameters of marine species allows a greater knowledge of the human impact, improving exploitation strategies of these resources. For example, the displacement capacity and mobility patterns are crucial to obtain the required knowledge for a sustainable management of fisheries.
However, underwater localisation is one of the main problems which must be addressed in subsea exploration, where no Global Positioning System (GPS) is available. In addition to the traditional underwater localisation systems, such as Long BaseLine (LBL) or Ultra-Short BaseLine (USBL), new methods have been developed to increase navigation performance, flexibility, and to reduce deployment costs. For example, the Range-Only and Single-Beacon (ROSB) is based on an autonomous vehicle which localises and tracks different underwater targets using slant range measurements conducted by acoustic modems. In a moving target tracking scenario, the ROSB target tracking method can be seen as a Hidden Markov Model (HMM) problem. Using Bayes' rule, the probability distribution function of the HMM states can be solved by using different filtering methods. Accordingly, this thesis presents different strategies to improve the ROSB localisation and tracking methods for static and moving targets. Determining the optimal parameters to minimize acoustic energy use and search time, and to maximize the localisation accuracy and precision, is therefore one of the discussed aspects of ROSB. Thus, we present and compare different methods under different scenarios, both evaluated in simulations and field tests. The main mathematical notation and performance of each algorithm are presented, where the best practice has been derived. From a methodology point of view, this work advances the understanding of accuracy that can be achieved by using ROSB target tracking methods with autonomous vehicles.
Moreover, whereas most of the work conducted during the last years has been focused on target tracking using acoustic modems, here we also present a novel method called the Area-Only Target Tracking (AOTT). This method works with commercially available acoustic tags, thereby reducing the costs and complexity over other tracking systems. These tags do not have bidirectional communication capabilities, and therefore, the ROSB techniques are not applicable. However, this method can be used to track small targets such as jellyfish due to the reduced tag's size. The methodology behind the area-only technique is shown, and results from the first field tests conducted in Monterey Bay area, California, are also presented.La biologia marina junt amb la importància que ha adquirit el sector pesquer, fa que es requereixin noves eines per a l’estudi dels nostres oceans. La capacitat de mesurar diferents poblacions i paràmetres ambientals d’espècies marines permet millorar el coneixement de l’impacte que l’ésser humà té sobre elles, millorant-ne els mètodes d’explotació. Per exemple, la capacitat de desplaçament i els patrons de moviment són crucials per obtenir el coneixement necessari per a una explotació sostenible de les pescaries involucrades. No obstant, la localització submarina és un dels principals problemes que s’ha de resoldre en l’explotació dels recursos submarins, on el sistema de posició global (GPS) no es pot utilitzar. A part dels mètodes tradicionals de posicionament submarí, com per exemple el Long Base-Line (LBL) o el Ultra-Short Base-Line (USBL), nous mètodes han estat desenvolupats per tal de millorar la navegació, la flexibilitat, i per reduir els costos de desplegament. Per exemple, el Range-Only and Single-Beacon (ROSB) utilitza un vehicle autònom per a localitzar i seguir diferents objectius submarins mitjançant mesures de rang realitzades a partir de mòdems acústics. En un escenari on l’objectiu a seguir és mòbil, el mètode ROSB de seguiment pot ser vist com a un problema de Hidden Markov Model (HMM). Aleshores, utilitzant la regla de Bayes, la funció de distribució de probabilitat dels estats del HMM pot ser solucionat utilitzant diferents mètodes de filtratge. Per tant, s’estudien diferents estratègies per millorar el sistema de localització i seguiment basat en ROSB, tant per objectius estàtics com mòbils. En aquesta tesis, presentem i comparem diferents mètodes utilitzant diferents escenaris, els quals s’han avaluat tant en simulacions com en proves de camp reals. A més, es presenten les principals notacions matemàtiques de cada algoritme i les millors pràctiques a utilitzar. Per tant, des d’un punt de vista metodològic, aquest treball fa un pas endavant en el coneixement de l’exactitud que es pot assolir utilitzant els mètodes de localització i seguiment d’espècies mitjançant algoritmes ROSB i vehicles autònoms. A més a més, mentre molts dels treballs realitzant durant els últims anys es centren en l’ús de mòdems acústics per al seguiment d’objectius submarins, en aquesta tesis es presenta un innovador mètode anomenat Area-Only Target Tracking (AOTT). Aquest sistema utilitza petites etiquetes acústiques comercials (tag), la qual cosa, redueix el cost i la complexitat en comparació amb els altres mètodes. Addicionalment, gràcies a l’ús d’aquests tags de dimensions reduïdes, aquest sistema permet seguir espècies marines com les meduses. La metodologia utilitzada per el mètode AOTT es mostra en aquesta tesis, on també es presenten els primers experiments realitzats a la badia de Monterey a Califòrnia
Underwater Vehicles
For the latest twenty to thirty years, a significant number of AUVs has been created for the solving of wide spectrum of scientific and applied tasks of ocean development and research. For the short time period the AUVs have shown the efficiency at performance of complex search and inspection works and opened a number of new important applications. Initially the information about AUVs had mainly review-advertising character but now more attention is paid to practical achievements, problems and systems technologies. AUVs are losing their prototype status and have become a fully operational, reliable and effective tool and modern multi-purpose AUVs represent the new class of underwater robotic objects with inherent tasks and practical applications, particular features of technology, systems structure and functional properties
Boundary tracking and source seeking of oceanic features using autonomous vehicles
The thesis concerns the study and the development of boundary tracking and source seeking approaches for autonomous vehicles, specifically for marine autonomous systems. The underlying idea is that the characterization of most environmental features can be posed from either a boundary tracking or a source seeking perspective. The suboptimal sliding mode boundary tracking approach is considered and, as a first contribution, it is extended to the study of three dimensional features. The approach is aimed at controlling the movement of an underwater glider tracking a three-dimensional underwater feature and it is validated in a simulated environment. Subsequently, a source seeking approach based on sliding mode extremum seeking ideas is proposed. This approach is developed for the application to a single surface autonomous vehicle, seeking the source of a static or dynamic two dimensional spatial field. A sufficient condition which guarantees the finite time convergence to a neighbourhood of the source is introduced. Furthermore, a probabilistic learning boundary tracking approach is proposed, aimed at exploiting the available preliminary information relating to the spatial phenomenon of interest in the control strategy. As an additional contribution, the sliding mode boundary tracking approach is experimentally validated in a set of sea-trials with the deployment of a surface autonomous vehicle. Finally, an embedded system implementing the proposed boundary tracking strategy is developed for future installation on board of the autonomous vehicle. This work demonstrates the possibility to perform boundary tracking with a fully autonomous vehicle and to operate marine autonomous systems without remote control or pre-planning. Conclusions are drawn from the results of the research presented in this thesis and directions for future work are identified
Design of an autonomous underwater vehicle : vehicle tracking and position control.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.This project proposes the development of an autonomous underwater vehicle that can be used to perform underwater research missions..The vehicle can be pre-programmed to complete a specified mission. Missions may include underwater pipe inspection, a survey of the sea floor or just the transport of given sensors to a certain depth or position and take measurements of underwater conditions. The Mechatronics and Micro Manufacturing group at the CSIR is engaged in developing a portfolio of autonomous vehicles as well as fur-
ther research into the development and implementation of such vehicles. Underwater vehicles will form part of the portfolio of autonomous vehicle research. Autonomous underwater vehicles (AUVs) are mostly used for research purposes in oceanographic studies as well as climate studies. These scientists use AUVs to carry a payload of sensors to specified depths and take measurements of underwater conditions, such as water temperature, water salinity or carbon levels as carbon is being released by plankton or other ocean organisms. Very little information is available about what is happening below the surface of the oceans and AUVs are being used to investigate this relatively unknown environment. The area covered by the world's ocean is 361 million km2 with an average depth of 3790 m. The deepest surveyed depth point in the ocean is at a depth of about 11 000 m at the southern end of the Mariana Trench in the Pacific Ocean. This just shows the need for research into
this mostly unexplored world. Research and exploration in the oceans can be achieved through the use of autonomous underwater vehicles. A big problem to overcome is the fact that GPS is not available for navigation in an underwater environment. Other sensors need to be found to be used for navigational purposes. The particular vehicle developed for this study will be used to facili-
tate further research into underwater vehicle navigation and underwater robotics
Towards a 3D hydrodynamic characterization from the joint analysis and blending of multiplatform observations for potential marine applications in the southeastern Bay of Biscay
277 p.La necesidad de un mayor conocimiento y una gestión sostenible de las áreas costeras ha suscitado la instalación de observatorios que monitorizan su estado. A pesar de que la información aportada por estos observatorios es esencial la compleja hidrodinámica de estas áreas dificulta una completa caracterización de las mismas. Además, la cobertura espacial de las observaciones es, en general, relativamente escasa especialmente en la columna de agua. Por tanto, el objetivo de esta tesis es combinar los datos disponibles de diferentes plataformas de observación en el sureste del Golfo de Bizkaia proporcionados por el sistema de oceanografía operacional de la costa vasca (EuskOOS) y también por fuentes externas para caracterizar en 3D la hidrodinámica de la zona. Para ello se han analizado conjuntamente las diferentes observaciones disponibles y se han utilizado métodos de reconstrucción de datos que permiten expandir dichas observaciones en 3D. Las observaciones conjuntas permiten detectar los principales procesos hidrodinámicos como los remolinos o la corriente de talud. Por otro lado, se observa que el usode los métodos de reconstrucción evaluados es factible en el área, especialmente el de la interpolación óptima de orden reducido (ROOI). Las observaciones y las corrientes reconstruidas por el ROOI han permitido caracterizar un remolino en 3D en el área de estudio por primera vez. Además, los campos de corrientes reconstruidos han posibilitado simular la advección superficial y subsuperficial de huevos y larvas de anchoa en la zona, mostrando el potencial del ROOI para aplicaciones marinas
- …