Browsing by Author "Zabel, Friedrich"
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- Automatic acoustic target detection and classification off the Coast of PortugalPublication . Sabara, Razi; Soares, Cristiano; Zabel, Friedrich; Valente de Oliveira, José; Jesus, SergioOcean noise has been a topic of research for many years, for its impact in sonar detection, underwater communications and ocean acoustic observation in general. Recently, ocean sound has been designated as an Essential Ocean Variable (EOV) and is therefore, becoming increasingly recorded and monitored, along with other oceanic and meteorological variables. The research projects EMSO-PT and SUBECO aim at deploying ocean observatories along the coast of Portugal for long term ocean variables monitoring, among which ocean sound. Unlike other ocean variables, ocean sound allows for feature detection, characterisation and possibly identification with known patterns. This work shows the results obtained with current machine learning algorithms for feature detection and extraction on a two days recording of ocean noise obtained on a offshore buoy deployed under the SUBECO project, on the west coast of Portugal. Preliminary results show the possibility of improved event detection, followed by classification and clustering, that foresee a rapid and accurate analysis of large observatory acquired acoustic data sets.
- Baseline assessment of underwater noise in the Ria FormosaPublication . Soares, C; Pacheco, André; Zabel, Friedrich; G-Gorbeña, Eduardo; Sequeira, ClaudiaThe Ria Formosa is a sheltered large coastal lagoon located on the Atlantic South Coast of Portugal, that has been classified as a natural park since 1987. The lagoon hosts a diverse and abundant fish community and other species of commercial importance. Several economical activities are supported by shipping, and as such, vessel traffic within the Ria Formosa lagoon is very intense at some locations during particular seasons of the year, creating high levels of underwater noise. Recently, strong efforts are being made to turn the main inlet of the lagoon, the Faro-Olhão Inlet, a testing site for small scale tidal stream turbines, which will bring an additional source of underwater noise. Underwater noise can be one of a number of factors causing habitat degradation, as it can perturb fish behavior and cause physiological damage. Therefore, in order to comply with underwater noise pollution regulations, tidal energy technology developers are very interested in minimising the introduction of acoustic energy in the environment during the operation of their devices. Under the scope of project SCORE, which involved the deployment and operation of a floating tidal energy converter, this paper presents and discusses the first baseline noise monitoring performed at Ria Formosa. The acoustic data were collected in two occasions over several days, one in the winter and the other in the summer, in 2017. The obtained analysis results highlight the potential impact of the intense boat traffic in Ria Formosa, and the wide range of sound levels introduced in that ecosystem, and the high diurnal and seasonal variability.
- Comparing noise vessel azimuth tracking with a planar hydrophone array and a single vector sensorPublication . SOARES, CRISTIANO; Zabel, Friedrich; Jorge Maia dos Santos, Paulo; Silva, AntónioVector sensors are appealing for monitoring underwater noise due to its inherent directivity. While acoustic pressure sensors are ambiguous in all directions, vector sensors permit the aquisition of directional information through the measurement of particle velocity, which enables the possibility of azimuth tracking of underwater noise sources. The MARREAL marine observatory is a marine observatory equipped with a number of sensors and subsystems, including an acoustic acquisition system made of four hydrophones and a vector sensor. The observatory was deployed in September 2022 in Sagres, Portugal, near the Baleeira Port which is accessed by fisher boats and recreational boats. This paper shows preliminary results on azimuth estimation of boats passing in the deployment area, obtained independently with a 4- hydrophone planar array and a vector sensor. The results indicate that a single vector sensor can provide fair results on azimuth tracking of boats passing in the area. At high signal-to-noise ratio (SNR) the vector sensor is able to yield results similar to those obtained with the planar array. When the SNR is low the planar array outperforms the vector sensor with actual processing methods used.
- A Demonstrator for future fiber-optic active SMART repeatersPublication . Cruz, Nuno A.; Silva, António; Zabel, Friedrich; Ferreira, Bruno; Jesus, Sergio; Martins, Marcos S.; Pereira, Eduardo; Matos, Tiago; Viegas, Ruben; Rocha, João; Faria, JoãoThe deep-sea environment still presents many challenges for systematic, comprehensive data acquisition. The current generation of SMART cables incorporates low-power sensors in long-range telecommunication cables to improve knowledge of ocean variables, aid in earthquake and tsunami warnings, and enhance coastal protection. The K2D Project seeks to expand SMART cables' capabilities by increasing the diversity of sensors along deep water cables, integrating active devices, and leveraging mobile platforms like deep-water AUVs, thereby improving spatial coverage and advancing ocean monitoring technology. This paper discusses a demonstration of these capabilities, focusing on the description of the main building blocks developed along the project, with results from a sea deployment in September 2023.
- Development and testing of a dual accelerometer vector sensor for AUV acoustic surveysPublication . Mantouka, Agni; Felisberto, Paulo; Santos, Paulo; Zabel, Friedrich; Saleiro, Mário; Jesus, Sergio M.; Sebastiao, LuisThis paper presents the design, manufacturing and testing of a Dual Accelerometer Vector Sensor (DAVS). The device was built within the activities of theWiMUST project, supported under the Horizon 2020 Framework Programme, which aims to improve the efficiency of the methodologies used to perform geophysical acoustic surveys at sea by the use of Autonomous Underwater Vehicles (AUVs). The DAVS has the potential to contribute to this aim in various ways, for example, owing to its spatial filtering capability, it may reduce the amount of post processing by discriminating the bottom from the surface reflections. Additionally, its compact size allows easier integration with AUVs and hence facilitates the vehicle manoeuvrability compared to the classical towed arrays. The present paper is focused on results related to acoustic wave azimuth estimation as an example of its spatial filtering capabilities. The DAVS device consists of two tri-axial accelerometers and one hydrophone moulded in one unit. Sensitivity and directionality of these three sensors were measured in a tank, whilst the direction estimation capabilities of the accelerometers paired with the hydrophone, forming a vector sensor, were evaluated on a Medusa Class AUV, which was sailing around a deployed sound source. Results of these measurements are presented in this paper.
- Development of a high-power multilayer PVDF acoustic projector for 40 to 80 kHz bandPublication . Silva, António; Hughes, Ashley; Pozzatti, Daniel; Zabel, Friedrich; Viegas, Rúben; Martins, MarcosA piston type projector using the PVDF piezoelectric polymer was developed for operating in underwater environment, below 100 kHz. For those frequencies PZT piezoelectric ceramic is usually a preferable choice and PVDF is only considered for frequencies above a few hundreds of kHz. This paper will show that efficient underwater acoustic projectors for frequencies below 100 kHz can be implemented regarding an appropriate impedance adapter is being used. The developed project presents a calibrated transmitting voltage response (TVR) of approximately 166, 160 and 175 dB at 40, 50 and 75 kHz, respectively. The PVDF TVR values are compatible with the PZT projectors available on market with the advantage of having a larger bandwidth than most PZT projectors. To the authors knowledge this is the first time that a PVDF projector attain such characteristics. Although theoretically the PVDF projector bandwidth is larger than 40 to 80 kHz, in practice it was observed that only between those frequencies the project presents a stable operation for the transmission of long-term signals.
- In-Lab demonstration of an underwater acoustic spiral sourcePublication . Viegas, Rúben; Zabel, Friedrich; Silva, AntónioUnderwater acoustic spiral sources can generate spiral acoustic fields where the phase depends on the bearing angle. This allows estimating the bearing angle of a single hydrophone relative to a single source and implementing localization equipment, e.g., for target detection or unmanned underwater vehicle navigation, without requiring an array of hydrophones and/or projectors. A spiral acoustic source prototype made out of a single standard piezoceramic cylinder, which is able to generate both spiral and circular fields, is presented. This paper reports the prototyping process and the multi-frequency acoustic tests performed in a water tank where the spiral source was characterized in terms of the transmitting voltage response, phase, and horizontal and vertical directivity patterns. A receiving calibration method for the spiral source is proposed and showed a maximum angle error of 3° when the calibration and the operation were carried out in the same conditions and a mean angle error of up to 6° for frequencies above 25 kHz when the same conditions were not fulfilled.
- INOVPESCA - Redução de capturas acidentais de espécies marinhas protegidas em pescarias costeiras algarvias: inovação de procedimentos e técnicas de mitigaçãoPublication . Marçalo, Ana; Carvalho, Flávia; Frade, Magda; Pires, Alexandra; Alexandre, Sofia; Bentes, Luis; Soares, Cristiano; Zabel, Friedrich; Rangel, Mafalda; Oliveira, Frederico; Monteiro, Pedro; Ressurreição, Adriana; Erzini, Karim; M. S. Gonçalves, JorgeO presente relatório é uma iniciativa do Projecto iNOVPESCA, com o objetivo de documentar o trabalho desenvolvido ao longo do projeto (2018-2021) e incentivar a implementação voluntária de medidas que contribuam para uma melhoria da relação entre as pescas e as espécies marinhas protegidas, especialmente de cetáceos, contribuindo para a sustentabilidade ambiental com a redução de capturas acidentais e sustentabilidade económica do sector das pescarias costeiras Algarvias, podendo servir de exemplo a nível nacional. Este trabalho pretende ser um documento de referência sobre o nível de interação que existe entre pescarias costeiras ao longo da costa algarvia com espécies marinhas protegidas (cetáceos, aves marinhas e tartarugas), e por outro lado, pode servir como aconselhamento para todas as entidades que beneficiam das pescas e que necessitam desta atividade para o seu desenvolvimento económico e social. Para isso foi desenvolvida uma linha de orientação sobre boas práticas assente em dois aspetos chave: - Contribuir para a consciencialização, informação e treino de todas as partes interessadas, no que se refere a medidas de mitigação de conflitos entre pescas e espécies marinhas protegidas; - Promover o uso de práticas responsáveis de pesca e otimizar, em cooperação com o sector pesqueiro, soluções que ajudem a diminuir a mortalidade acidental de cetáceos ou outras espécies protegidas (ex. aves marinhas e tartarugas marinhas) e evitar situações que contribuam para perdas económicas para o pescador (como por exemplo, danos nas artes e perda ou danos no pescado por predação). As interações entre espécies marinhas protegidas e as pescas são um problema mundial com duas componentes importantes, a da conservação, quando os animais como captura não intencional ficam presos nas artes de pesca acabando por morrer, e a socioeconómica quando os animais causam danos nas artes de pesca e na captura alvo dos pescadores.
- Integrated approach for modeling acoustic propagation and projectors/hydrophones electronicsPublication . Viegas, Rúben; Pozzatti, Daniel; Zabel, Friedrich; Silva, AntónioUnderwater acoustic propagation models (APM) are useful tools to predict acoustic propagation, making it possible to implement and test equalization algorithms for Underwater Acoustic Communication (UWAC) systems. To our knowledge, none of the APMs developed so far consider the distortion induced by the associated electronic circuits, impedance adaptors and acoustic transducers on signal propagation, which are important mainly in broadband applications. This paper describes the functioning of a new model capable of predicting the aforementioned distortions on the projector and hydrophone. The electro-Acoustic Propagation Model (eAPM) calculates the frequency response of the circuits with frequency-dependent characteristic components (transducers and impedance adaptors) using SPICE simulations and simulates the acoustic propagation using an Time-Variable APM (TV-APM), all embedded in a single model. SPICE simulations require the insertion of electrical impedance measurements from the transducers and impedance adaptors. eAPM also uses the projector's Transmitting Voltage Response (TVR) and the hydrophone's Open Circuit Voltage Response (OCVR), that can be obtained through equipment calibration. The model output signals have a good agreement with the signal experimentally recorded, showing that the eAPM allows for in-lab prediction of the distortion induced by the transducers and electronics and its impact on an application in a realistic acoustic propagation environment. The developed model can be used to predict distortions on broadband UWAC systems and also to support the development of new transducers, especially those with a wide bandwidth response.
- A methodology for shipping noise field calibration and excess noise estimation: the Azores case studyPublication . Jesus, Sergio; Soares, Cristiano; Romagosa, Miriam; Cascão, Irma; Duarte, Ricardo; Zabel, Friedrich; Silva, Mónica A.Economic globalization and the continuous search for food, energy and raw materials led to an estimated 3 dB/decade increase of ocean noise intensity. Determining the level of anthropogenic noise, the so-called excess noise, and building identifiable meaningful indicators for supporting marine management policies currently requires extensive observation data and computer modeling. For modeling purposes, in this study, anthropogenic noise was reduced to shipping traffic drawn from Automatic Identification System data, and environmental sound was attributed to surface wind only. Data-model comparison allowed introducing a methodology for simple model calibration and estimate excess noise. This methodology was tested on acoustic recordings performed in June 2018 at three locations to the southwest of Faial-Pico Islands in the Azores archipelago. The results show that field-calibrated excess noise sound maps are in line with the shipping distribution in the area, revealing a number of potentially marine life-threatening hotspots. Excess noise addresses the need for a quantifiable measure of ocean noise only and therefore offers a basis for building suitable continuous anthropogenic noise pollution indicators.