SiPLABoratory

LOCAPASS project - MREA'03 sea trial and achievements

1. Theoretical study: in this phase it was proved, using previously acquired real data, that it is indeed possible to passively localize a sound source using a 4-hydrophone array in an unknown sound speed profile area [Felisberto 2003]. With a larger number of sensors it becomes possible not only to localize the sound source but also the physical properties of the media where the acoustic wave is propagating [Jesus 2002a, Jesus 2002b, Soares 2002a, Soares 2003a]. Amongst the sound sources localized during these tests there are also surface ships of opportunity. This work lead to 2 journal publications and 7 presentations in international conferences with peer review and proceedings, one of them invited (see publications ).

2. Plan and assembling of the data receiving system: being concluded that it was more expensive and much more complex to modify an existing system than to assemble a new system, it was decided to start the planning of a acoustic receiving system from scratch. Therefore the Acoustic Oceanographic Buoy, actually in its version 0 - AOB.V0, was developed. The AOB has as main characteristic to be a light and easy to handle system, and with reduced dimensions. In future versions, it will converge to the weight and dimensions of a sonobuoy. However it will have a much higher number of acoustic channels than a standard sonobuoy (4 in current version 0 and up to 8 in the next versions) and a wide frequency band up to 15 kHz, allowing for its usage in sonar detection, source localization, tomography, acoustic rapid environmental assessment (AREA) and underwater communications.

	AOBuoy in R/V Alliance's deck, June 23, 2003, north of Elba I. (Italy). Weight: 90 Kg Dimensions: height - 1.30 m; diameter: 23 cm; mast: 2.30 m Hydrophones: 4 (15, 60, 75 e 90 m) Band: 10 - 15000 Hz Storage: 60 GB Communications: wireless lan 2.4 GHz (1w) Localization: GPS with time base precision of 1 micro sec
	AOBuoy: mast with antennas and radar reflector GPS antenna for real time localization and time synchronization (1 micro sec) Wireless lan antenna: monopole 2.4 GHz, 1W amplifier
	AOBuoy: top cover Top cover with: mast base, GPS and wireless lan antennas, pass-through for Ethernet (100 Mb/s) and power supply connectors.
	AOBuoy: bottom cover Bottom cover: hydrophone connections and time-delayed ON/OFF switch after touching sea water. The array is connected to the center of the structure.
	AOBuoy: hydrophone array Acoustic array in the R/V ALLIANCE's deck prior to deployment. (June 21, 2003)
	AOBuoy: hydrophone Hydrophone: piezo-electrical sensor with integrated pre-amplifier, band 100-15000 Hz, sensitivity -190 dB.

3. MREA'03 sea trial: due to successive delays in the programmed sea trials of the Instituto Hidrográfico, it was decided to test the AOB.v0 during the MREA'03 sea trial organized by the NATO Saclantcen Undersea Research Centre, La Spezia, Italy, in the area of north Elba I., during June 2003. Participating in this sea trial took place as a preliminary test under the scope of the upcoming REA - Joint Research Project, to which CINTAL/UALg is a partner. Other partners of this JRP are: the Université Libre de Bruxelles (ULB), the Instituto Hidrográfico (IH) and the Royal Netherlands Naval College (RNLNC).

	Deploying the AOBuoy aboard the R/V ALLIANCE. Elba I. (Italy), June 23, 2003
	The AOBuoy after deployment on June 23, 2003 during the MREA'03 sea trial.
	Recovering the AOBuoy aboard of R/V ALLIANCE, June 23, 2003
	The SiPLAB/UALg work team and the AOBuoy during the MREA'03 sea trial, aboard the R/V ALLIANCE, north Elba I. (Italy). June 21, 2003.

Acknowledegments

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To the participants in the sea trial Cristiano Soares and António Silva, to Saclantcen, to the Master and crew of the R/V ALLIANCE , to the scientist in charge of the MREA'03, E. Ferreira Coelho, Saclantcen personnel and finally the collaboration of J.P. Hermand (ULB e RNLNC) with the pictures taken during the sea trial.

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