Source Localization In Shallow Water Research Articles

Source localization in a partially known shallow‐water channel

The source localization in shallow water is beset with problems arising from the presence of a large number of correlated multipaths. Nevertheless, given a complete knowledge of the water channel it is definitely possible to localize a source. A complete knowledge of the channel, however, is rarely available under most practical conditions. A new approach is proposed wherein the bottom reflection coefficients are not required; hence the bottom conditions need not be known. Further, because of the use of signal subspace for localization, the proposed approach is robust against the background noise (−20 dB) and channel depth uncertainty (10λ). All these nice features of the proposed approach are possible only when the array size is large (≳40 sensors).

A mode subspace approach for source localization in shallow water

Abstract Range and depth source localization in shallow water amounts to the estimation of the normal mode structure of the acoustic field. The new technique presented in this paper uses the spectral decomposition of the sample covariance matrix in order to estimate the mode subspace spanned by the normal modes that are significantly excited by the source. Simulation results obtained using realistic environments show that the technique's performance is always better than or equal to that of the generalized maximum likelihood processor.

On subspace method for source localization

A method of source localization in shallow water, based on subspace concept, is described. It is shown that a vector representing the source in the image space spanned by the direction vectors of the source images is orthogonal to the noise eigenspace of the covariance matrix. Computer simulation has shown that a horizontal array of eight sensors can accurately localize one or more uncorrelated sources in shallow water dominated by multipath propagation.

A new method for range and depth source localization in shallow water

Range and depth source localization in shallow water amounts to the estimation of the normal mode structure of the acoustic field. As “seen” by a vertical array, and from a modeling point of view, the normal mode structure appears as a set of nonplane coherent waves closely spaced in angle. The technique presented in this paper uses the eigen decomposition of the data cross‐correlation matrix in order to resolve this set of nonplane waves and to estimate the subspace spanned by the normal modes that are significantly excited by the source(s): the mode subspace. The projection of the replica pressure vector onto the mode subspace for all possible range/depth source locations gives the final ambiguity surface. Results obtained on realistic environments show that its performance is always greater or equal to that of the generalized MLM processor [A. B. Baggeroer, W. A. Kuperman, and H. Schmidt, J. Acoust. Soc. Am. 83, 571–587 (1988)]. Good performance results have been obtained on short time records; this suggests the method may be applicable to localizing moving sources and/or sources emitting transient signals. Preliminary results obtained on real data will be discussed and compared with those obtained by the conventional and MLM processors.

Environmental and system effects on source localization in shallow water by the matched-field processing of a vertical array

This paper presents simulated and experimental results on source localization in shallow water by the matched-field processing of a vertical array. Range-depth ambiguity surfaces are obtained by the spatial correlation of the incident field (modeled or real) with a modeled replica of that field. All modeled fields are generated by the Centre’s normal-mode program. The simulated results indicate that a high-quality ambiguity surface can be obtained provided that the incident field is formed by a significant number of contributing modes, and that the array spans a large fraction of the water column. Changes in the acoustic environment that reduce the effective number of modes result in a degraded surface. The effect of mismatches between the ‘‘true’’ environmental parameters and those used to compute the replica field is also investigated. Errors in the bottom parameters do not severely effect the results, but small mismatches in sound-speed profile or water depth can degrade the result significantly. Examples of localizations obtained with real data from a Mediterranean site are presented, for source ranges up to 19 km from a vertical array that spanned half the water depth. Successful localizations were obtainable, though high sidelobes were also present.