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Classification of three-dimensional ocean features using three-dimensional empirical orthogonal functions

European Conference on Underwater Acoustics 2010, vol. 1, pp. 341-347

N. Martins1,
L. Calado2,
A.C. de Paula2,
S.M. Jesus1,
1Institute for Systems and Robotics, University of Algarve
Campus de Gambelas, PT-8005-139 Faro, Portugal
2Institute of Marine Studies Admiral Paulo Moreira
Rua Kioto, 253, Praia dos Anjos, 28930-000 Arraial do Cabo, RJ, Brazil
Ref.: European Conference on Underwater Acoustics 2010

Abstract: Water column properties are routinely estimated by acoustic tomography. The problem is ill-conditioned and computationally intensive, if each spatial point varies freely in the inversion. Empirical orhogonal functions (EOFs) efficiently regularize the inversion, leading to a few (2, 3) coefficients to estimate, giving a coherent estimate of the field. At small scales, EOFs are typically depth-dependent basis functions. The extension of the concept to larger-scale anisotropic fields requires horizontal discretization into cells, with corresponding coefficients. This becomes unstable and computationally heavy, having been overcome by two-dimensional depth-range EOFs, in the past. The present work extends the empirical orthogonal function concept to three dimensions, assessing the performance of the inversion for an instantaneous sound speed field constructed from measures off Cabo Frio, Brazil. The results show that the large-scale features of the field are correctly estimated, though with strong ambiguity, using an acoustic source tens of km from an acoustic hydrophone array. Work is under progress, to remove the ambiguity and estimate finer details of the three-dimensional field, via the addition of acoustic arrays.

ACKNOWLEDGMENT: this work was partially supported by the project WEAM (PTDC/ENR/70452/2006), the scholarship no. SFRH/BD/9032/2002, under the POSI, POCTI and POCI programs, from FCT, Portugal, and the EU OAEx Marie Curie FP7-PEOPLE-IRSES-2008 Program.