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- Geoacoustic matched-field inversion using a vector sensor arrayPublication . Santos, P.; Felisberto, P.; Rodríguez, O. C.; Jesus, S. M.Vector sensors measure the acoustic pressure and the particle velocity components. This type of sensor has the ability to provide information in both vertical and azimuthal direction allowing increased directivity. These characteristics have been explored by many authors and most of the studies on vector sensors found in literature are related to direction of arrival (DOA) estimation. However, assembled into an array, a Vector Sensor Array (VSA) improves spatial filtering capabilities and can be used with advantage in other applications such as geoacoustic inversion. In this paper it will be shown that a reliable estimation of ocean bottom parameters, such as sediment compressional speed, density and compressional attenuation, can be obtained using high-frequency signals and a small aperture vertical VSA. The introduction of particle velocity on matched-field processing (MFP) techniques is going to be presented. It will be seen how MFP, usually done with acoustic pressure, can be adapted in order to incorporate the three components of the particle velocity. Comparisons between several processors based either in individual particle velocity components or using all the VSA outputs, are made for simulated and experimental data. The quaternion model, which is founded on hypercomplex algebra, thus more appropriate to represent the 4 dimensional VSA data, is also presented in the MFP context. A novel ray tracing model is used to generate field replicas that include both the acoustic pressure and the particle velocity outputs. The data considered herein was acquired by a four element vertical VSA in the 8-14 kHz band, during the Makai Experiment 2005 sea trial, off Kauai I., Hawaii (USA). The results shows that, when the particle velocity is included it can significantly increase the resolution of bottom properties estimation and in some cases a similar result is obtained using only the vertical component of the particle velocity.
- Matched field processing with a vector sensor arrayPublication . Santos, P.The main objective of this report is to present a particle velocity-pressure joint data model and a version of Bartlett estimator in order to include the particle velocity in Matched- eld inversion tecnhiques. Both data model and estimator will be used in the estimation of bottom parameters such as: the compressional wave speed, the compressional attenuation and the density of sediment, where the simulations results are pro- vided by the TRACE ray tracing model, capable for particle velocity outputs.
- Estimating bottom properties with a vector sensor array during the Makai 2005 experimentPublication . Santos, P.; Felisberto, P.; Jesus, S. M.Nowadays, vector sensors which measure both acoustic pressure and particle velocity begin to be available in underwater acoustic systems, normally configured as vector sensor arrays (VSA). The spatial filtering capabilities of a VSA can be used, with advantage over traditional pressure only hydrophone arrays, for estimating acoustic field directionality as well as arrival times and spectral content, which could open up the possibility for its use in bottom properties' estimation. An additional motivation for this work is to test the possibility of using high frequency probe signals (say above 2 kHz) for reducing size and cost of actual sub bottom profilers and current geoacoustic inversion methods. This work studies the bottom related structure of the VSA acquired signals, regarding the emitted signal waveform, frequency band and source-receiver geometry in order to estimate bottom properties, specially bottom reflection coefficient characteristics. Such a system was used during the Makai 2005 experiment, off Kauai I., Hawai (USA) to receive precoded signals in a broad frequency band from 8 up to 14 kHz. The agreement between the observed and the modelled acoustic data is discussed and preliminary results on the bottom reflection estimation are presented.
- Modelação acústica submarina de alta frequência baseada em traçamento de raios: revisão teórica e aplicações actuaisPublication . Rodríguez, O. C.; Santos, P.; Jesus, S. M.Nos ultimos anos a evolução dos sistemas electrónicos de processamento de sinal, que combinam uma alta potência de cálculo com um tamanho reduzido, tem permitido o desenvolvimento de sistemas acústicos submarinos que operam a altas frequências (acima de 1 kHz); tais sistemas permitem o processamento e ciente do sinal recebido em antenas com sistemas simples, ou compostos, de hidrófonos. Em paralelo com a vertente de engenharia aplicada tem-se assistido ao reviver do interesse de modelação, relacionada com a utilização de modelos de traçamento de raios; tais modelos permitem a modelação a altas frequências com um tempo de cálculo, compatível com as necessidades de um sistema que deve responder em tempo real. O intenso desenvolvimento das aplicações e dos modelos não tem sido por em acompanhado pela uniformização teórica das diferentes aspectos da modelação, o que dificulta o desenvolvimento de aplicações dos modelos em simulações e em dados reais. Os objectivos principais deste documento consistem em apresentar uma revisão teórica dos modelos de traçamento de raios, em abordar alguns dos problemas numéricos envolvidos na aplicação dos modelos, e em mostrar aplicações concretas, baseadas nos modelos TRACE e TRACEO actualmente em desenvolvimento no SiPLAB.
- Sistema automático de medida usando o sistema GSMPublication . Santos, P.Este artigo apresenta um sistema automático de aquisição de dados com aplicação na monitorização da qualidade da água, não só do mar mas também de rios, lagos e lagoas. É um instrumento ambiental bastante útil, baseado numa estação de medida situada numa bóia que envia os dados via GSM para uma estação em Terra.
- Source localization with vector sensor array during the makai experimentPublication . Santos, P.; Felisberto, P.; Hursky, PaulVector sensors measure both the acoustic pressure and the three components of particle velocity. Because of this, a vector sensor array (VSA) has the advantage of being able to provide substantially higher directivity with a much smaller aperture than an array of traditional scalar (pressure only) hydrophones. Although several, most of them theoretic, works were published from early nineties, only in the last years due to improvements and availability of vector sensor technology, the interest on field experiments with VSA increased in the scientific community. During the Makai Experiment, that took place off the coast of Kauai I., Hawaii, in September 2005, real data were collected with a 4 element vertical VSA. These data will be discussed in the present paper. The acoustic signals were emitted from a near source (low frequency ship noise) and two high frequency controlled acoustic sources located within a range of 2km from the VSA. The advantages of the VSA over traditional scalar hydrophone arrays in source localization will be addressed using conventional beamforming.
- Vector sensor array data report: Makai Ex 2005Publication . Santos, P.This report describes the data acquired with a Vector Sen- sor Array (VSA) during the Makai Ex 2005, that took place aboard the R/V Kilo Moana from 15 September to 2 October, 2005, o the coast of Kauai I. (Hawai), United States. The orientation of the axis on VSA, a study of direction of arrival estimation and bottom properties estimation are included.
- Estimating bottom properties with a vector sensor array during MakaiEx 2005Publication . Santos, P.; Felisberto, P.; Jesus, S. M.Nowadays, vector sensors which measure both acoustic pressure and particle velocity begin to be available in underwater acoustic systems, normally configured as vector sensor arrays (VSA). The spatial filtering capabilities of a VSA can be used, with advantage over traditional pressure only hydrophone arrays, for estimating acoustic field directionality as well as arrival times and spectral content, which could open up the possibility for its use in bottom properties' estimation. An additional motivation for this work is to test the possibility of using high frequency probe signals (say above 2 kHz) for reducing size and cost of actual sub bottom profilers and current geoacoustic inversion methods. This work studies the bottom related structure of the VSA acquired signals, regarding the emitted signal waveform, frequency band and source-receiver geometry in order to estimate bottom properties, specially bottom reflection coefficient characteristics. Such a system was used during the Makai 2005 experiment, off Kauai I., Hawai (USA) to receive precoded signals in a broad frequency band from 8 up to 14 kHz. The agreement between the observed and the modelled acoustic data is discussed and preliminary results on the bottom reflection estimation are presented.