Acoustic tomography ocean monitoring system ATOMS

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Publications

Spring-summer climatological circulation in the upper layer in the region of Cape St. Vincent, Southwest Portugal

Publication . Sanchez, R. F.; Relvas, Paulo

Geostrophic transport and hydrographic measurements derived from a historical database (1900-1998) were used to study the spring-summer mean circulation in the upper layer south and west of Cape St. Vincent, Southwest (SW) Portugal. The larger-scale circulation scheme is forced by equatorward winds from May to September, when the Iberian coastal transition zone (CTZ) is dominated by a generalized upwelling of cold, low-salinity water. A partially separated surface jet intensified at the shelf break conveys similar to1 Sv of upwelled water equatorward parallel to the bathymetry, while offshore a poleward flow transports similar to0.4-0.6 Sv of upwelled water. Although alongshore transports dominate the circulation pattern of the upper layers, cross-shore transports are significant at the climatological scale. Anticyclonic circulation with an exchange of similar to0.5 Sv from the equatorward jet to the offshore poleward flow and the partial re-circulation further north, back into the equatorward flow are discussed. A coherent, cyclonic re-circulation pattern inshore of the upwelling jet is also speculated. From these results the shelf break is considered a climatological border at both sides of which two major re-circulation cells occur. The climatological equatorward flow has offshore protrusions, interpreted as recurrent episodes of major contortions of the upwelling flow. These features bring about considerable "cross-shelf flow" re-circulation reaching up to 50% of the main flow. The most significant exchanges are found to be associated with major changes of orientation of the coastline. Off Cape St. Vincent the upwelling front stretches to both west and south and contributes to the cross-shelf re-circulations. Additionally, convergence of the upwelling flow and a branch of the Azores current, with associated re-circulation is found diagonally from the cape. On the southern coast the upwelling jet is seen to meander offshore in the vicinity of Cape St. Maria. Individual synoptic cruise data showed agreement with the climatological circulation features. We conclude that these oceanographic features leave an imprint on the climatic circulation in spite of the "smoothing out" of recurrent events over the spring-summer period of the years of 1900-1998. (C) 2003 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

2003-12Journal article

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Broadband matched-field tomography using simplified acoustic systems

Publication . SOARES, CRISTIANO; Jesus, S. M.

Ocean Acoustic Tomography is a remote sensing technique that has been proposed to infer physical properties of the ocean traversed by the sound field. Although its feasibility has been demonstrated, it is still not being used in a systematic way due, in a large extent, to cost and operational difficulties of standard acoustic systems. Current developments of acoustic systems go in the sense of simplifying them, both at the emitting and receiving end. Simplifying an acoustic system may represent a loss or a reduction of the amount of information contained in the observed acoustic field, possibly conducting to degradation in the inversion results. The objective of this thesis is to adapt existing array processing methods to be used in acoustic tomography and geoacoustic inversion taking into account the challenges posed by such simplifications, and to cope with the loss of available information they may represent. Two aspects are exploited with the objective of coping with the reduction of information: one is the development of a broadband data model, and the other is the development of matched-field processors based on that broadband data model, with particular emphasis in highresolution processors. Matched-field based approaches appear to be suitable to work in conjunction with the simplified acoustic systems used to collect several experimental data sets treated herein. Experimental results using simplified acoustic systems, sparse receiving arrays (active mode) on one hand, or an uncontrolled source (passive mode) on the other hand, show that it is possible to produce environmental estimates of the watercolumn and seafloor in close agreement with ground truth measurements.

2007Doctoral thesis

Open Access

Estimation of the properties of a range-dependent ocean environment. A simulation study

Publication . Corré, V.

This report describes a simulation study to estimate the range and depth variations of ocean acoustic properties. The estimation is based on matched- eld inversion. Results show the feasibility of detecting the presence of an abnormaltemperature water entity.

2001Report

Open Access

The INTIFANTE'00 sea trial: preliminary source localization and ocean tomography data analysis

Publication . Jesus, S. M.; Coelho, E.; Onofre, J.; Picco, P.; Soares, C.; Lopes, C.

The INTIFANTE'00 sea trial was a multidisciplinary experiment including testing of an autonomous surface vehicle, underwater communications, source localization and acoustic ocean tomography. The results shown here will concentrate on the source localization and ocean tomography data sets. The data gathered during a 24 hour run along a range independent track shows strong oceanographic features, possibly due to internal tide signature, both on the temperature data, as measured on the thermistor chain collocated with a vertical line array(VLA), and on the acoustic data. A range dependent track between 120 and 60 m water depth, shows a highly variable channel impulse response along time and range when the source was moving outwards from the VLA. In another acoustic track, the source was navigatated across a underwater canyon where the energy was rapidly distributed over a deep acoustic channel with sound trapped well below the thermocline. Good agreement between the modeled and measured channel responses represents the rst step towards matched- eld processinglike methods such as source localization and tracking and ocean tomography.

2001Book part

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Basin scale simulations of ocean acoustic tomography in the Portuguese exclusive economic zone

Publication . Rodríguez, O. C.

This internal report describes some of the experiments developed in the eld of Ocean Acoustic Tomography, simulation results regarding the acoustic monitoring of the Portuguese Economic Exclussive Zone and a brief description of binary m-sequences.

2002Report

Open Access