Acoustic maritime rapid environmental assessment 2004 during the MREA'04 sea trial

Rep 02/05 - SiPLAB 21/Mar/2005Environmental inversion of acoustic signals for bottom and water column properties is being proposed in the literature as an interesting concept for complementing direct hydrographic and oceanographic measurements for Rapid Environmental Assessment (REA). The acoustic contribution to REA can be cast as the result of the inversion of ocean acoustic properties to be assimilated into ocean circulation models specifically tailored and calibrated to the scale of the area under observation. Traditional ocean tomography systems and methods for their requirements of long and well populated receiving arrays and precise knowledge of the source/receiver geometries are not well adapted to operational Acoustic REA (AREA). The Acoustic Oceanographic Buoy (AOB) was proposed as an innovative concept that responds to the operational requirements of AREA. That concept includes the development of water column and geo-acoustic inversion methods being able to retrieve environmental true properties from signals received on a drifting network of acoustic-oceanographic sensors - the AOBs. An AOB prototype and a preliminary version of the inversion code, was tested at sea during the Maritime Rapid Environmental Assessment 2003 (MREA’03) sea trial and was reported in [1]. On a separate register it should be noted that the characterization of the environment between the source and the receiver also contributes to the identification of the acoustic channel response and therefore provides a basis for fulfilling the objectives of project NUACE1. The present report describes the data sets and results gathered during the MREA’04 sea trial that took place from 29 March to 19 April 2004 off the west coast of Portugal, south of Lisboa (Portugal), with the objectives of testing an improved version of the individual AOB and its functionality in a simple network. The acoustic part of the experiment lasted for four days between April 7 and April 10, 2004 and involved the transmission and reception of pre-coded signals along range-dependent and range-independent acoustic tracks.This report presents recent developments on the AOB system and the results obtained during its testing in the MREA’04 sea trial. The MREA’04 sea trial took place off the Portuguese coast, approximately 50 km south from Lisbon, in the period 29 March - 19 April, 2004. The authors of this report would like to thank: • the NATO Undersea Research Centre for the opportunity for participating in the sea trial • the scientist in charge Dr. Emanuel Coelho • the collaboration of Saclantcen personnel • the master and crew of the R/V Alliance • the contribution of Prof. J.-P. Hermand and Mathias Meyer from ULB for the assistance, contribution and thoughtfull discussions. • FCT (Portugal) for the funding provided under project NUACE (POSI/CPS/47824/ 2002)