2014
Autores
Alves, JC; Cruz, NA;
Publicação
SEA TECHNOLOGY
Abstract
The demand for accurate ocean sampling is continuously growing to provide a better understanding of the complex sea environment. Current economic and social activity is strongly dictated by knowledge built on data collected from thousands of sensors around the world, ranging from space-borne remote sensors to underwater devices transported by profilers. Autonomous sailboats have great potential to gather long-term data to understand multiple aspects of the ocean environment. In terms of oceanography, they can be used to study many processes occurring at the surface, like the energy exchange between the ocean and the atmosphere and how it affects the climate. They can also be a valuable tool to understand the dynamics of episodic events that evolve on a timescale of weeks or months, like harmful algae blooms or the evolution of pollution plumes. Even though these incidents can already be tracked by satellite, the ability to capture in-situ data for the full cycle can provide valuable data about the phenomena.
2016
Autores
Valente, JF; Alves, JC;
Publicação
OCEANS 2016 MTS/IEEE MONTEREY
Abstract
The direction of arrival of sound waves has been extensively used for passive acoustic tracking of underwater sound sources, such as marine mammals or ultrasonic electronic tags attached to animals or submerged equipment. This process can be automated by measuring the time difference of arrival (TDOA) of the sound wave arriving to two or more hydrophones and then calculating the relative direction of the acoustic source using those time differences. Although the generalized cross-correlation between the received signals is a common technique for determining the TDOA, the underwater environment introduces several distortions in amplitude and phase of the received sound waves due to reflections and reverberation, particularly in confined spaces. This is aggravated by the variation of the sound propagation speed with temperature, pressure and salinity. Because of this, the use of the cross-correlation method not effective to determine the TDOA especially when using single frequency pulses as the transmitted signal. In this work we propose an alternative method to calculate the TDOA, consisting in the analysis of the initial part of the received signals to discover a series of similar zero-crossing periods to identify their beginning, and then calculating the time difference between them. We have implemented this technique in a reconfigurable system-on-chip, attaching to an embedded ARM processor a custom designed digital signal processing system. This has been tested in a test tank and in outside environment. This system is capable of computing in real-time the 2D direction of an underwater acoustic transmitter, and combining the different directions resulting from the relative movement between transmitter and receiver it is possible to estimate the relative position of the acoustic source.
2017
Autores
Cruz, N; Abreu, N; Almeida, J; Almeida, R; Alves, J; Dias, A; Ferreira, B; Ferreira, H; Gonçalves, C; Martins, A; Melo, J; Pinto, A; Pinto, V; Silva, A; Silva, H; Matos, A; Silva, E;
Publicação
OCEANS 2017 - ANCHORAGE
Abstract
This paper describes the PISCES system, an integrated approach for fully autonomous mapping of large areas of the ocean in deep waters. A deep water AUV will use an acoustic navigation system to compute is position with bounded error. The range limitation will be overcome by a moving baseline scheme, with the acoustic sources installed in robotic surface vessels with previously combined trajectories. In order to save power, all systems will have synchronized clocks and implement the One Way Travel Time scheme. The mapping system will be a combination of an off-the-shelf MBES with a new long range bathymetry system, with a source on a moving surface vessel and the receivers on board the AUV. The system is being prepared to participate in round one of the XPRIZE challenge.
2019
Autores
Truppel, A; Tseng, TM; Bertozzi, D; Alves, JC; Schlichtmann, U;
Publicação
PROCEEDINGS OF THE 2019 INTERNATIONAL SYMPOSIUM ON PHYSICAL DESIGN (ISPD '19)
Abstract
Optical Networks-on-Chip (ONoCs) are a promising solution for high-performance multi-core integration with better latency and bandwidth than traditional Electrical NoCs. Wavelength-routed ONoCs (WRONoCs) offer yet additional performance guarantees. However, WRONoC design presents new EDA challenges which have not yet been fully addressed. So far, most topology analysis is abstract, i.e., overlooks layout concerns, while for layout the tools available perform Place & Route (P&R) but no topology optimization. Thus, a need arises for a novel optimization method combining both aspects of WRONoC design. In this paper such a method, PSION, is laid out. When compared to the state-of-the-art design procedure, results show a 1.8x reduction in maximum optical insertion loss.
2019
Autores
Machado da Silva, JM; Carlos Alves, JC;
Publicação
2019 XXXIV CONFERENCE ON DESIGN OF CIRCUITS AND INTEGRATED SYSTEMS (DCIS)
Abstract
An alternative approach to compute the signal to noise ratio of analogue to digital converters based on the computation of the cross-correlation coefficient of the captured response is proposed here. It is shown, after simulation and experimental results, that this approach allows obtaining good accuracy results with the added advantages of not requiring coherent sampling and high purity sine wave stimuli.
2018
Autores
Santos, PV; Alves, JC; Ferreira, JC;
Publicação
U.Porto Journal of Engineering
Abstract
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