PROPAGATION AND ANALYSIS ISSUES IN THE PREDICTION OF LONG-RANGE REVERBERATION

Data collected from the Office of Naval Research-special research prog ram (ONR-SRP) bottom reverberation research cruises consist of various environmental measurements (sound-speed profiles, bottom properties, etc.), extensive bathymetric mapping of the 300 km X 150 km natural la boratory, and high-quality acoustic reverberation data recorded in bot h monostatic and bistatic geometries. The analysis of the acoustic dat a and the effects of propagation are investigated. Accurate GPS tracki ng of the participating research vessels provided the precision necess ary to attempt to correlate ''spiky'' reverberation events with bathym etric features. Understanding the limitations of our ability to resolv e such features-due to imperfect signal processing, environmental vari ability, and complex multipath structures-is the main objective of thi s work. Using a simplified time-to-range conversion, the measured reve rberation data can be displayed over the local bathymetry. This proces s shows good correlation between large-scale [O(km)] high-level return s and bathymetric ridge structures. Employing a PE propagation model i n a quasi-cw manner, many of the large-scale reverberation features ca n be shown to correlate well with predicted high-level ensonification of the total field [low transmission loss (TL)]. Extending the model p redictions to include time domain broadband pulse propagation, it can be shown for ranges greater than similar to 20 km that multipaths and forward scatter produce complex ensonification patterns which are unre solvable in time and/or range. The effect of this on the ability to co rrelate finer scale returns and bathymetric features will be discussed . Preliminary analysis of data from a bottom mounted vertical array in the vicinity of 1/2 CZ exhibits strong evidence for the existence of these predicted multipaths and provides a means of confirming the rela tive intensities predicted by propagation models. (C) 1996 Acoustical Society of America.