Environmental inversion using high-resolution matched-field processing

C. Soares and S.M. Jesus csoares@ualg.pt sjesus@ualg.pt
SiPLAB - FCT, Universidade do Algarve,
Campus de Gambelas,
PT-8005-139 Faro, Portugal.

E. Coelho coelho@nrlssc.navy.mil
Emanuel F. Coelho
Naval Research Laboratory
Code 7322, Bldg 1009, Room C128
Stennis Space Center, MS39529

Ref.: Journal of the Acoustical Society of America, (submitted; revised).

Environmental inversion of acoustic signals for seafloor and water column properties has been proposed as a concept for complementing direct oceanographic measurements for Rapid Environmental Assessment (REA). In order to respond to operationality requirements of acoustic REA a light receiver device, an Acoustic Oceanographic Buoy (AOB) with a sparse vertical array, was developed under the AOB-REA Joint Research Project. Inversion methods based on Matched-Field Processing appear to be suitable to be applied under those requirements. However, if a reduced number of receivers is available to sample the vertical normal modes of the acoustic field, then the inverse problem is heavily ill-conditioned, whereas the underlying cost-function may have a massive sidelobe structure with many local extrema. This causes difficulties to meta-heuristic search methods, such as a genetic algorithm, to converge to the true model parameters. In order to cope with this difficulty broadband high-resolution processors are proposed for their ability to significantly attenuate sidelobes, under the belief that this can contribute for improving convergence. A minimum-variance and a subspace based method are applied to the inversion of synthetic and experimental acoustic data using a sparse array, and compared to a Bartlett processor. Their effectiveness in multi-parameter estimation problems is clearly demonstrated.

Acknowledgement: The authors would like to thank the NATO Undersea Research Centre for the organization of the MREA'03 sea trial. This work was financed by FCT, Portugal, under fellowship SFRH/BD/12656/2003 and NUACE project, contract POSI/CPS/47824/2002, and the Portuguese Ministery of Defense under the LOCAPASS project.