17 documents found, page 1 of 2
A Demonstrator for future fiber-optic active SMART repeaters
Cruz, Nuno A.; Silva, António; Zabel, Friedrich; Ferreira, Bruno; Jesus, Sergio; Martins, Marcos S.; Pereira, Eduardo; Matos, Tiago; Viegas, RubenThe 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 o...
Spiral beacon calibration and experiments for underwater localization
Viegas, Rúben; Zabel, Friedrich; Gomes, João; Silva, AntónioUnderwater localization and navigation are still challenging tasks due to the underwater acoustic channel characteristics. Spiral sources are underwater transducers that create structured acoustic fields from which the angle to the source can be readily obtained. The angle estimation is obtained from the phase difference between transmitted circular and spiral fields, but for reliable operation the transducers ...
Underwater localization using time and frequency multiplexing of circular and s...
Viegas, Rúben S.; Zabel, Friedrich; Silva, António; Gomes, JoãoThe transmission of circular and spiral acoustic fields using spiral beacons offers a promising alternative to traditional underwater localization methods. Existing literature typically employs time multiplexing of these field types. This work introduces a novel approach by implementing both time and frequency multiplexing of circular and spiral fields, specifically transmitting three circular and one spiral fi...
Underwater acoustic spiral source: pool tests and calibration
Viegas, Sergio; Zabel, Friedrich; Silva, AntónioUnderwater acoustic spiral sources are able to generate spiral acoustic fields where the phase depends on the bearing angle. It allows to estimate the bearing angle relatively to a receiver by subtracting the phases of a spiral and a circular wavefront, and can be used to estimate bearing angles with a single hydrophone/projector pair, e.g., for unmanned underwater vehicles localization. The developed spiral so...
In-Lab demonstration of an underwater acoustic spiral source
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 prototyp...
Comparing noise vessel azimuth tracking with a planar hydrophone array and a si...
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 wi...
A methodology for shipping noise field calibration and excess noise estimation:...
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...
Development of a high-power multilayer PVDF acoustic projector for 40 to 80 kHz...
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 ap...
Integrated approach for modeling acoustic propagation and projectors/hydrophone...
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 ...
Baseline assessment of underwater noise in the Ria Formosa
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 par...