Prediction of the acoustic propagation loss in shallow water is complicated by the thermal variability in the water column and by the bottom loss on the fluid-elastic interface. In this study, a coupled environment and acoustic prediction system was developed for evaluation of the acoustic propagation in shallow water. The acoustic prediction system uses the range-dependent, parabolic-equation (PE) IFD model. Since, the IFD model is restricted to the fluid bottom, an equivalent fluid bottom approximation was made to incorporate the elastic medium into the IFD model. Specifically, the actual reflection coefficient at fluid-elastic interface, calculated by the range-independent, seismo-acoustic SAFARI model, was approximated at low grazing angles by a new set of fluid parameters (density, attenuation and P-wave speed). It was shown that this approach had error ;The environment (coastal ocean) system was based on the model simulation of temperature field in the northern California shelf for the upwelling season. The solid bottom geoacoustic parameters were derived from the geoacoustic model using the sediment and seismic profile data. Numerical simulations were performed to quantify the variability of acoustic propagation due to coastal thermal field. The study found that the acoustic propagation loss had significant change (5 dB difference) during the spring transition, but was less sensitive to the upwelling-relaxation cycle. This was due to the fact that on the northern California shelf for the study periods, significant changes of sound velocity characteristic in the lower water column only occurred during the spring transition. The study also found that the acoustic propagation had higher loss for shallow source depth and low frequency. The present approach allows a systematic and realistic evaluation of the acoustic variability in shallow water.
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