Broadband matched-field processing of transient signals in shallow water

S.M. Jesus

SACLANT Undersea Research Centre,
Viale SAn Bartolomeo 400,
I-19138 La Spezia, Italy.

Comments: download pdf file .
Ref.: Journal of the Acoustical Society of America, 93(4), Pt.1, p. 1841-1850, 1993.

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 non-plane coherent waves closely spaced in vertical angle. This paper presents a full-wavefield narrowband high-resolution technique that uses the spectral decomposition of the sample covariance matrix to resolve the vertical arrival structure of the harmonic acoustic field. The broadband processor is obtained by weighted averaging of the narrowband range-depth ambiguity estimates within the source signal frequency band. Results obtained on synthetic data show that its performance is always better than or equal to that of the generalized minimum variance processor, which itself largely outperforms the conventional matched-field processor. It is shown, using both simulated and experimental data, that the effect of the broadband processor is to increase the stability of the source location estimate. Results obtained with this processor on short transient pulses collected during the North Elba'89 experiment with a 62 m aperture vertical array, showed stable and accurate localizations over long time intervals. It is also shown that the sound field, received over a given frequency band, is relatively stable over time and is in agreement with the predictions given by a standard normal-mode propagation model.