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Publications

Estimating the multipath structure of an underwater channel using a single vector sensor

Publication . Felisberto, P.; Rodríguez, O. C.; Jesus, S. M.

This paper aims at estimating the multipath structure of an underwater acoustic channel using a single vector sensor. The multipath structure of an underwater acoustic channel measured by a single hydrophone from broadband signals is used for source localization or environmental monitoring applying model based methods. Generally in a first step the relative delays between the different echoes impinging the hydrophone and their amplitudes are estimated, then those are compared with a propagation model outputs for a given set of input parameters. Usually this requires a number of time consuming propagation model runs and an optimization procedure. A vector sensor measures the pressure and the particle velocity, thus in addition to delays and amplitudes estimated by a hydrophone can potentially estimate the direction (azimuth and elevation) of the different echoes in an impulse response. This additional information can be used to significantly reduce the number of propagation model runs and simplify the optimization procedure. Although, the estimate of the azimuth is relatively straightforward using a single vector sensor, the estimate of the elevation of the different echoes is difficult due to the signal bandwidth, low amplitude of the latter arrivals or sensitivity to phase errors of available devices, among others. This paper discusses the estimates of the direction of individual echoes observed in impulse responses gathered during the Makai'05 sea trial in the context of single vector sensor model based localization (azimuth, range and depth).

2011Conference object

Open Access

cTraceo User Manual

Publication . Emanuel, E.; Rodríguez, O. C.

This internal report describes the C port of the gaussian beam raytracing model TRACEO.

2012Report

Open Access

Ocean parameter estimation with high-frequency signals using a vector sensor array

Publication . Santos, P.; Jesus, S. M.; Felisberto, P.

Vector sensors began to emerge in 1980s as potential competitors to omni directional pressure driven hydrophones, while their practical usage in underwater applications started in the last two decades. The crucial advantage of vector sensors relative to hydrophones is that they are able to record both the omni-directional pressure and the three vectorial components of the particle velocity. A claimed advantage of vector sensors over hydrophones is the quantity of information obtained from a single point spatial device, which potentially allows for high performance small aperture Vector Sensor Arrays (VSA). The capabilities of such small aperture VSA have captured the attention for their usage in high-frequency applications. The main contribution of this work is the understanding of the gain provided by vector sensors over hydrophones whenever ocean environmental parameter estimation is concerned. In a rst step a particle velocity-pressure joint data model is proposed and an extended VSA-based Bartlett estimator is derived. This data model and estimator, initially developed for estimating direction of arrival, are generalized for ocean parameter estimation, assuming a particle velocity capable physical model - the TRACEO model. The highlighted capabilities of the VSA are rst demonstrated for angle of arrival estimation, where a variety of spatial con gurations of hydrophone arrays are compared to that of a vertical VSA. A vertical VSA array con guration is then used for estimating geoacoustic bottom properties from short range acoustic data, using two VSA-based techniques: the generalized Bartlett estimator and the re ection coe cient estimator proposed by Harrison et al.. The proposed techniques where tested on experimental VSA data recorded in shallow water area o the Island of Kauai (Hawaii) during the MakaiEx 2005 experiment. The obtained results are comparable between techniques and inline with the expected values for that region. These results suggest that it is indeed possible to obtain reliable seabed geoacoustic properties' estimates in a frequency band of 8-14 kHz using a small aperture VSA with only a few sensors.

2012Doctoral thesis

Open Access

Comparing the resolution of Bartlett and MVDR estimators for bottom parameter estimation using pressure and vector sensor short array data

Publication . Felisberto, P.; Schneiderwind, J.; Santos, P.; Rodríguez, O. C.; Jesus, S. M.

This work compares the resolution of a pressure and vector sensor based conventional Bartlett estimator, with their MVDR estimator counterparts, in the context of bottom characterization with a short vertical array. Santos et al. [1]demonstrated the gain of a vector sensor array (VSA) based linear estimator (Bartlett) for generic parameter estimation. Moreover, it was shown that for bottom characterization the highest resolution of the estimates were achieved with the vertical particle velocity measurements alone. The present work highlights the gain in parameter resolution of a VSA based MVDR estimator. It is shown, that also for a MVDR estimator, the vector sensor array data improves the resolution of parameter estimation. But, it is also shown, through simulations, that for bottom parameter estimation, the pressure based MVDR estimator has higher resolution and sidelobe attenuation than the VSA based Bartlett estimator. These results were verified for experimental data acquired by a four element, 30 cm long vertical VSA in the 8–14 kHz band, during the Makai Experiment 2005 sea trial, off Kauai I., Hawaii (USA).

2013Conference object

Open Access

Localização de fontes acústicas com um Vector Sensor Array

Publication . João, J.; Felisberto, P.

Tradicionalmente, os sistemas de aquisição de dados utilizados na acústica submarina são constituídos por antenas lineares de hidrofones, os quais medem a pressão acústica, sendo esta uma grandeza escalar. Em aplicações típicas de sonar, alguns sistemas têm sido concebidos utilizando antenas de sensores vectoriais (“Vector Sensor Array”-VSA), os quais, além da pressão acústica medida pelos tradicionais hidrofones medem a velocidade das partículas sobre três eixos ortogonais. Uma vantagem dos sensores vectoriais é a sua capacidade de filtragem espacial intrínseca, permitindo a resolução da ambiguidade esquerda-direita inerente às antenas lineares de hidrofones. A partir da campanha MakaiEx’05, demonstrou-se com dados reais que uma antena com poucos sensores, no caso quatro, permite estimar a direcção de chegada (azimute e elevação) de sinais em várias bandas de frequência. Pode-se então conjecturar que utilizando uma antena de sensores vectoriais e aplicando métodos de “Match Field Processing” se consiga obter uma localização tridimensional de uma fonte acústica onde, para além do azimute, se determine a distância e a profundidade. No presente trabalho, estuda-se a aplicação desse conceito à localização tridimensional do ruído de um navio, aplicado aos dados da referida campanha MakaiEx’05. Uma vez que a localização da fonte é conseguida com antenas de poucos elementos, este tipo de sistemas poderá ser indicado para diferentes aplicações onde seja requisito a utilização de sistemas compactos, por exemplo em AUVs (Autonomous Underwater Vehicle) ou outras pequenas plataformas móveis.

2011Master thesis

Open Access