Source localization with vector sensor array during the makai experiment

Vector 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

Mapeamento espacial de perturbações da temperatura do oceano por integração sistemática de dados acústicos e medições in-situ

O conhecimento das perturbações da temperatura/velocidade do som numa área do oceano é de primordial importância para um vasto conjunto de aplicações, entre as quais se contam o sonar, as pescas, etc. O método clássico utilizado para construir essa imagem da temperatura do oceano baseia-se em medições in-situ com recurso a equipamentos tais como o CTD, XBT e cadeia de termistores. Este método fornece informação com alta resolução nos pontos onde se realizam as medições, sendo todavia moroso para construir uma imagem espacial. Mais recentemente, a tomografia acústica submarina, desenvolveu métodos para inferir perturbações da temperatura/velocidade do som do oceano a partir de transmissões acústicas. Um dos aspectos relevantes da tomografia acústica é que uma medição cobre todas as perturbações que ocorrem entre o emissor e o receptor acústico, os quais podem estar a distâncias da ordem das dezenas de quilómetros ou mais. Estas perturbações são integrais, isto é reflectem uma média das perturbações observadas ao longo do canal de propagação. Historicamente, os dois métodos têm sido tratados independentemente, embora a sua integração possa potencialmente permitir ganhos em termos de custos e disponibilidade da informação. Neste trabalho apresentaremos um método de mapeamento espacial de perturbações da temperatura que integra de forma sistemática a informação obtida por tomografia acústica e medições in-situ. Serão apresentadas simulações da aplicação do método a situações realísticas descritas na literatura e observadas nas campanhas de mar em que participou o Laboratório de Processamento de Sinais da Universidade do Algarve. Discutiremos o método apresentado do ponto de vista da distribuição dos diferentes equipamentos de aquisição, o que poderá ser utilizado no planeamento de campanhas de mar

Vector sensor arrays in underwater acoustic applications

Traditionally, ocean acoustic signals have been acquired using hydrophones, which measure the pressure field and are typically omnidirectional. A vector sensor measures both the acoustic pressure and the three components of particle velocity. Assembled into an array, a vector sensor array (VSA) improves spatial filtering capabilities when compared with arrays of same length and same number of hydrophones. The objective of this work is to show the advantage of the use of vector sensors in underwater acoustic applications such as direction of arrival (DOA) estimation and geoacoustic inversion. Beyond the improvements in DOA estimation, it will be shown the advantages of using the VSA in bottom parameters estimation. Additionally, is tested the possibility of using high frequency signals (say 8-14 kHz band), acquired during the MakaiEx 2005, to allow a small aperture array, reducing the cost of actual sub-bottom profilers and providing a compact and easy-to-deploy system

Tracking source azimuth using a single vector sensor

This paper aims at estimating the azimuth of an underwater acoustic source with a single vector sensor. A vector sensor is a device that measures the scalar acoustic pressure field and the vectorial acoustic velocity field at a single location in space. The actual sensor technology allows to build compact vector sensors, with an operational frequency response ranging from a few hertz to several tens of kilohertz, thus the same device can be used to receive shipping noise upto dolphin whistles. It is demonstrated that one can attain a reliable estimate of the azimuth of a source with a single vector sensor. The method presented is based on the inner product between the sampled acoustic field and the different particle velocity orthogonal components. The method is very simple and low computational demanding thus, well suited to be used in mobile or light platforms where space and/or computational power requirements is of concern. It is shown that the proposed method can be used either in time or in frequency domain, giving rise to easily estimating the azimuth of several sources with non-overlapping frequency bands. The data discussed herein (ship noise, communication signals, tomographic signals) were acquired during the Makai’2005 experiment using a four element vector sensor array. It is shown that the estimates obtained with a single vector sensor are comparable with those obtained with the full vector sensor array and are inline with the expected results as known from the geometry of the experiment

Estimating bottom properties with a vector sensor array during MakaiEx 2005

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

Ultra light vertical array remote data acquisition system

SiPLAB Report 03/05, FCT, University of Algarve,2005.In the framework of the ATOMS project, a project devoted to study uppwelling processes off the S. Vicente Cape, Portugal, by oceanographic and acoustic means, it was requested to adapt an existent underwater acoustic acquisition system named Ultra Light Vertical Array (ULVA) to fulfil the project requirements. The ULVA system was a vertical instrumented with up to 16 hydrophones and various non-acoustic sensors (thermistors, tiltmeters and pressure gauges). The ULVA system was used during the INTIFANTE project sea trial, where the acquired data were transmitted through a radio link to a remote PC station located in a vessel for storage, monitoring and online processing. In order to overcome data loses due to radio link fails, identified during the INTIFANTE sea trial, and improve the mobility of the vessel where the PC station is located, a must for the ATOMS project, it was decided to transform the ULVA system into an autonomous acquisition system with local storage facilities, lower power consumption, capability of on line remote quality control of the acquired data and positioning information. The first version of this new system, named Ultra Light Vertical Array/Remote Data Acquisition System (ULVA/RDAS), was described in the report. During the sea trial MREA'04 it was found that an auxiliary UHF radio link used to send some commands to the ULVA, like switch on/off the power or switch on/off the array electronics, remains a source of problems in the ULVA/RDAS. Thus, it was decided to remove the UHF link from the system, emulating its facilities by new developed hardware. In this new version (second) of the ULVA/RDAS system, it was also introduced a new monitoring software, in order to improve its robustness and share a common user interface with other SiPLAB acquisition systems. This report describes the actual ULVA/RDAS system (version 2) and is intended as a system reference and user guide.FC

Seagrass workshop sea trial data report

Rep 04/11 - SiPLAB October/2011The Seagrass Workshop sea trial took place in a very shallow water area in front of STARESO (Station the recherchessous-marines et oceanographiques), Punta la Revellata, Gulf of Calvi, Corsica from 10 to 19 October 2011, in the frameworkof the Action ES0906 (Seagrass productivity: from genes to ecosystem management) supported by the FP7 Programme COST (European Cooperation in the Field of Scienti c and Technical Research). During this multidisciplinary workshop the participating groups have sampled the Posidonia oceanica eld using di erent methods in order to characterize the seagras individuals and the whole community. This report describes the data gathered by the SiPLAB/Marsensing team, which objective is to characterize the in uence of seagrass oxygen production in acoustic propagation and develop techniques to estimate oxygen production by acoustic means

CALCOM'10 Sea Trial - field calibration data report

Rep 04/10 - SiPLAB November/2010The CALCOM'10 sea trial took place in a region SSE of Vilamoura from 22nd to 24th June to support WEAM & PHITOM projects. The rst day was devoted to equipment testing and calibration. The second and third days were devoted to eld calibration and underwater communications. This report refers to eld calibration data acquired 23rd June, Day 2, and 24th June, Day 3

Acoustic pressure and particle velocity for spatial filtering of bottom arrivals

This paper discusses the advantages of using a combination of acoustic pressure and particle velocitymotion for filtering bottom arrivals. A possible area of application is reflection seismology where, traditionally, the seismic image is extracted from the bottom-reflected broadband acoustic signals received on hydrophones. Since hydrophones are omnidirectional in nature, the received bottom returns are often contaminated by waterborne signals, sea surface reflections, and noise. A substantial part of the processing of the data is dedicated to filtering out these unwanted signals. Today, vector sensors allow us to measure both acoustic pressure and particle velocity motion in a single and compact sensor. The combination of pressure and particle velocity measured at a single location or particle velocity and particle velocity gradient at closely spaced locations allows for spatial beam steering to predetermined directions and filter out unwanted replicas from other directions. Moreover, this can be done at the sensor level, dramatically decreasing the offline processing. The spatial filtering capabilities of various pressure-pressure, particle velocity-particle velocity, and pressure-particle velocity combinations are analyzed in view of filtering the bottom arrivals. It is shown that the combination of pressure and vertical particle velocity and, particularly, the combination of vertical particle velocity and particle velocity gradient enhance bottom arrivals. Moreover, a simple steering procedure combining pressure and particle velocity components of a triaxial sensor allows us to determine the tridimensional structure of the acoustic field and the separation of the bottom reflections. The spatial selectivity of the various sensor combinations is shown with simulations and verified with experimental data acquired with 10 cm separated vector sensors in the 800-1250-Hz band, during the Makai 2005 sea trial, off Kauai Island, HI, USA.This work was supported by the European Union H2020 Research Program under WiMUST Project (Contract 645141).info:eu-repo/semantics/publishedVersio

Field calibration a tool for acoustic noise prediction. The CALCOM 10 data set

It is widely recognized that anthropogenic noise affects the marine fauna, thus it becomes a major concern in ocean management policies. In the other hand there is an increasing demand for wave energy installations that, presumably, are an important source of noise. A noise prediction tool is of crucial importance to assess the impact of a perspective installation. Contribute for the development of such a tool is one of the objectives of the WEAM project. In this context, the CALCOM’10 sea trial took place off the south coast of Portugal, from 22 to 24 June, 2010 with the purpose of field calibration. Field calibration is a concept used to tune the parameters of an acoustic propagation model for a region of interest. The basic idea is that one can significantly reduce the uncertainty of the predictions of acoustic propagation in a region, even with scarce environmental data (bathymetric, geoacoustic), given that relevant acoustic parameters obtained by acoustic inference (i.e. acoustic inversion) are integrated in the prediction scheme. For example, this concept can be applied to the classical problem of transmission loss predictions or, as in our case, the problem of predicting the distribution of acoustic noise due to a wave energy power plant. In such applications the accuracy of bathymetric and geoacoustic parameters estimated by acoustic means is not a concern, but only the uncertainty of the predicted acoustic field. The objective of this approach is to reduce the need for extensive hydrologic and geoacoustic surveys, and reduce the influence of modelling errors, for example due to the bathymetric discretization used. Next, it is presented the experimental setup and data acquired during the sea trial as well as preliminary results of channel characterization and acoustic forward modelling