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Ref.: SiPLAB Report 01/01, FCT, University of Algarve,2001.
The TOMPACO project (TOMPACO stands for ''TOMografia PAssiva COstiera'' - Passive Coastal Tomography), aims at developing and testing ocean tomography techniques for obtaining a dense space-time acoustic griding at low cost, by relaxing the control on the source signal and geometry. In practice this means using alternative acoustic sources readily available in the ocean such as, for example, the noise radiated by ships of opportunity close or crossing the area of interest. The main challenge faced by passive tomography, and therefore by TOMPACO, is to account for the unpredictability of the sound source in the tomographic procedure. That unpredictability relates both to the source emitted signal and to the source-receiver geometry. The study of the impact of these two factors in the acoustic tomographic inversion process is the main goal of the TOMPACO project.
The INTIFANTE'00 sea trial (INTIFANTE is a madeup acronym from INTImate and inFANTE) was carried out in the vicinity of Setúbal, situated approximately 50 km to the south of Lisbon, in Portugal, during the period from 9 to 29 October, 2000. This sea trial served a number of specific purposes under the leading projects INTIMATE and INFANTE, but one day was reserved to acquire acoustic data to test the passive tomography concept under the TOMPACO project. The experiment area was a rectangular box situated in the border of the continental platform with depths varying from 60 to 140 m and including a sharp submarine canyon (the Setúbal canyon) with depths reaching over 500 m. As an overview of the thecnical aspects involved in the experiment, it can be referred that acoustic signals were transmitted with an acoustic projector from on board NRP D. Carlos I and received on a moored 16 hydrophone-4m spacing Vertical Line Array (VLA). The acoustic aperture of the vertical array was located between 30 and 90 m in a 120 m water column. The acoustic signals received in the VLA were transmitted via an RF link to the research ship NRP D. Carlos I, processed, monitored and stored. Various signals were emitted by the sound projector ranging from linear frequency modulated (LFM) 2 second long up sweeps, to broadband computer generated white noise. Recordings were also made with the NRP D. Carlos I acting as source signal for the passive tomography testing purpose.