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Ref.: SiPLAB Report 04/07, FCT, University of Algarve,2007.
The project "Random Array of Drifting Acoustic Receivers" (RADAR) started in 2004 with the objective of developing a network of drifting acoustic-oceanographic buoys (AOBs) for ocean observation. During this project a receiving buoy prototype was developed and tested at sea in 2005 (MakaiEx). During 2006 a second prototype was produced for implementing the network tomography concept, tested at sea during April/May 2007 in the MREA/BP07 and now in the RADAR’07 sea trial from 9 to 15 July. The conceptual idea is to explore the spatially coherent capabilities of a series of vertical arrays at known positions and its ability to resolve the 3D temperature field along time both with known active sources and possibly with sources of opportunity. The slow movement of the receivers with time, uncertainty of source - receivers relative geometry and evolution through a potentially poorly known bathymetry are the main challenges faced by the inversion of the acoustic data for environmental parameters. Another requirement is that acoustic inversion should be made in nearly real time, or at least, in a time compatible with the evolution of ocean parameters being monitored. The RADAR07 took place from 9 to 15 July, 2007, in the continental platform, off the west coast of Portugal near the town of Setúbal, approximately 50 km south from Lisbon and involved the oceanographic ship NRP D. Carlos I, from the Portuguese Navy. The data collected included an extensive CTD survey for ocean circulation modelling, acoustic data covering a wide band from 500 Hz up to 15 kHz, received on the AOBs and on a slim vertical array (SLIVA) and used for network tomography as well as for high-frequency tomography and underwater acoustic communications.