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- Monitoring bubble production in a seagrass meadow using a source of opportunityPublication . Felisberto, Paulo; Rodríguez, Orlando; Silva, João P.; Jesus, Sergio; Ferreira, Hugo Q.; Ferreira, Pedro P.; Cunha, Maria E.; de los Santos, Carmen B.; Olivé, Irene; Santos, RuiUnder high irradiance, the photosynthetic activity of dense seagrass meadows saturates the water forming oxygen bubbles. The diel cycle of bubble production peaks at mid-day, following light intensity pattern. It is well known that bubbles strongly affect the acoustic propagation, increasing signal attenuation and decreasing the effective water sound speed, noticeable at low frequencies. Thus, the diurnal variability of bubbles may show an interference pattern in the spectrograms of low frequency acoustic signals. In an experiment conducted in July 2016 at the Aquaculture Research Station of the Portuguese Institute for the Sea and Atmosphere in Olhão, Portugal, the spectrograms of low frequency (<20kHz) broadband noise produced by water pumps in a pond of 0.48ha covered by the seagrass Cymodocea nodosa showed interference patterns that can be ascribed to the variability of the sound speed in the water. Preliminary analysis suggests that the daily cycle of bubble concentration can be inferred from these interference patterns.
- The TV-APM interface: a web service for collaborative modellingPublication . Rodríguez, Orlando; Silva, António J.; Zabel, Friedrich; Jesus, S. M.Current development of Internet access, together with available zero-cost Open Source applications (like, for instance, PHP, Python, etc.) can be integrated in order to minimize the constrains induced by the geographical separation of international centers, which collaborate in a given project. The advantage of such approach lies in the sharing of common analysis methods, without particular constrains to specific directions of analysis. The discussion presented in this paper describes the Time Variable Acoustic Propagation Model (TV-APM) web interface, which was created as a collaborative service of acoustic modeling for the participants of the PHITOM and UAN projects. This paper describes the general architecture of the interface, its current shortcomings and advantages, and presents a set of modeling results for short range acoustic propagation, which accounts for source–array and sea surface motion.
- Search space reduction for localization and tracking of an acoustic sourcePublication . Rodríguez, Orlando; Zhang, Lilun; Cheng, XinghuaExperimental data from the SACLANTCEN 1993 Mediterranean Experiment are reviewed to assess the reduction of the search space for the localization and tracking of an acoustic source in a three-dimensional environment. Key to this goal is the availability of an initial estimate of source range and depth (called the 2D initial guess); an ambiguous estimate of source bearing can be obtained from the 2D initial guess through Environmental Signal Processing, and the ambiguity can be removed by searching for the source only in the range/bearing regions where bearing estimates are higher. This search provides a new estimate of source range and a single bearing, which together with the estimate for source depth constitute the center of the reduced search space for source localization and tracking. The suggested approach is tested on experimental data from the SACLANTCEN experiment considering different frequencies, as well as a stationary and a moving source.
- Parallel ray tracing for underwater acoustic predictionsPublication . Calazan, Rogério; Rodríguez, Orlando; Nedjah, Nadia; Gervasi, O.; Murgante, B.; Misra, S.; Borruso, G.; Torre, C. M.; Rocha, A. M. A. C.; Taniar, D.; Apduhan, B. O.; Stankova, E.; Cuzzocrea, A.Different applications of underwater acoustics frequently rely on the calculation of transmissions loss (TL), which is obtained from predictions of acoustic pressure provided by an underwater acoustic model. Such predictions are computationally intensive when dealing with three-dimensional environments. Parallel processing can be used to mitigate the computational burden and improve the performance of calculations, by splitting the computational workload into several tasks, which can be allocated on multiple processors to run concurrently. This paper addresses an Open MPI based parallel implementation of a three-dimensional ray tracing model for predictions of acoustic pressure. Data from a tank scale experiment, providing waveguide parameters and TL measurements, are used to test the accuracy of the ray model and the performance of the proposed parallel implementation. The corresponding speedup and efficiency are also discussed. In order to provide a complete reference runtimes and TL predictions from two additional underwater acoustic models are also considered.
- TRACEO3D Ray tracing model for underwater noise predictionsPublication . Calazan, Rogério; Rodríguez, Orlando; Camarinha-Matos, L. M.; Parreira-Rocha, M.; Ramezani, J.Shipping noise is the main source of underwater noise raising concern among environmental protection organizations and the scientific community. Monitoring of noise generated by shipping traffic is a difficult challenge within the context of smart systems and solutions based on acoustic modeling are being progressively adopted to overcome it. A module of sound propagation stands as a key point for the development of a smart monitoring system since it can be used for the calculation of acoustic pressure, which can be combined with estimates of the source pressure level to produce noise predictions. This paper addresses the usage of the TRACEO3D model for application in such systems; the model validity is addressed through comparisons with results from an analytical solution and from a scale tank experiment. The comparisons show that the model is able to predict accurately the reference data, while a full-field model (normal mode-based, but adiabatic) is only accurate till a certain degree. The results show that TRACEO3D is robust enough to be used efficiently for predictions of sound propagation, to be included as a part of a smart system for underwater noise predictions.
- Kernel-function-based models for acoustic localization of underwater vehiclesPublication . Pinheiro, Breno C.; Moreno, Ubirajara F.; de Sousa, Joao T. B.; Rodríguez, OrlandoThis paper proposes a novel design for the localization system of autonomous underwater vehicles (AUVs) using acoustic signals. The solution presented exploits models based on kernel functions with two main purposes: 1) to reject outliers; and 2) to correct or improve accuracy of measurements. The localization system discussed is based on well-established techniques such as support vector data description (SVDD) and autoassociative kernel regression (AAKR) derived from machine learning theory that utilizes heuristic models for classification and regression tasks, respectively. By coupling the algorithm to the navigation system, we seek to reduce the sensitivity of the localization scheme to the reflected acoustic waves or fluctuations of underwater channel properties without modifying the solution used for data fusion or overloading the algorithm embedded in the vehicle. Data collected in the field with a light underwater vehicle (LAUV) were used to demonstrate the advantages of the proposed approach.
- Fundamentos de acústica submarinaPublication . Rodríguez, OrlandoA Acústica Submarina é uma área de investigação excepcionalmente interdisciplinar, que pela primeira vez encontra nesta obra um espaço de expressão em língua portuguesa; trata-se de uma obra que condensa 30 anos de investigação por parte do autor e investigadores associados da UALG, e que pretende servir como referência para o desenvolvimento de aplicações nas áreas de investigação que recorrem aos métodos da Acústica Submarina. Em contraste com a literatura da especialidade, escrita maioritariamente em inglês, esta obra recorre extensivamente a exemplos de programação em Python (linguagem de código aberto e multi-plataforma) para complementar a exposição dos conceitos. É um livro escrito para principiantes e especialistas, para biólogos, oceanógrafos, informáticos, engenheiros, físicos e matemáticos, para pessoal civil e da marinha.
- Ocean noise field-calibration constraints for deep sea miningPublication . de Oliveira Júnior, Luciano; Rodríguez, Orlando; Jesus, SergioThe EU Horizon project TRIDENT aims at developing a comprehensive study to improve the understanding of the activities related to deep sea mining as well as to develop observation methodologies, technologies required for impact forecast, and possible mitigation measures. In the framework of TRIDENT, the impact of the acoustic field will be assessed by deploying a fixed array of acoustic recorders in the surrounding of the mining activity on top of the Tropic Seamount to monitor the near field, while acoustic gliders equipped with hydrophones will provide the observations from the far field. In complement, noise models will be routinely used for predicting sound distribution requiring frequent calibration with field data with a suitable spatial coverage. This work proposes a methodology and tests the calibration capabilities for ocean noise modelling in the context of DSM activities, where the main objective is to define the best sampling strategy for a glider to record data for calibrating acoustic propagation models. The analysis of the broadband transmission loss from contrasting oceanographic conditions allowed the identification of regions of interest assuring the best use of the acoustic glider in the upcoming sea trial.