BROAD-BAND MATCHED-FIELD PROCESSING OF TRANSIENT SIGNALS IN SHALLOW-WATER

Range and depth source localization in shallow water amounts to the es timation 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 spa ced at a vertical angle. This paper presents a full-wave-field narrow- band high-resolution technique that uses the spectral decomposition of the sample covariance matrix to resolve the vertical arrival structur e of the harmonic acoustic field. The broadband processor is obtained by weighted averaging of the narrow-band range-depth ambiguity estimat es within the source signal frequency band. Results obtained on synthe tic data show that its performance is always better than or equal to t hat of the generalized minimum variance processor, which itself largel y outperforms the conventional matched-field processor. It is shown, u sing both simulated and experimental data, that the effect of the broa dband processor is to increase the stability of the source location es timate. Results obtained with this processor on short transient pulses collected during the North Elba'89 experiment with a 62-m-aperture ve rtical array, showed stable and accurate localizations over long time intervals. It is also shown that the sound field, received over a give n frequency band, is relatively stable over time and is in agreement w ith the predictions given by a standard normal-mode propagation model.