SOURCE LOCALIZATION IN A WEDGE SHAPED SHALLOW SEA

The present paper looks into the problem of localization of an acoustic source in shallow sea with a sloping bottom as found in the continental shelf area. A vertical array of sensors is used to receive the acoustic signals from the source including those travelling by different paths. A spectral matrix of the received signal is computed and it is then subjected to eigenvalue decomposition. The space spanned by the eigenvectors is partitioned into two subspaces, namely a signal subspace spanned by the eigenvector corresponding to the largest eigenvalue and a noise subspace spanned by the eigenvectors corresponding to repeated eigenvalues. The signal subspace is also spanned by a linear combination of direction vectors corresponding to all multipaths. These two subspaces are orthogonal. We exploit this property of orthogonality in the estimation of range, bearing and depth of a source. Some of the significant findings are as follows: (1) Unlike in the flat bottom channel it is now possible to measure the azimuth with respect to upslope or downslope direction. (2) The azimuth scan shows a sharp peak at the correct location for slope greater than 1-degrees. (3) A study of finite data effect has shown that the signal peak amplitude increases roughly at the rate of 3 dB per doubling of the number of snapshots. We have used a ray model for acoustic signal propagation in a range dependent channel. In general the ray description is valid at high frequency, but with appropriate beam displacement correction it is found that the ray description is as accurate as normal mode or exact field calculations. We have incorporated these corrections in our algorithm and have demonstrated improved performance.