Temporal variability of Signal Detection Range (SDR) with respect to measured noise level and sound speed is examined. An N x 2D acoustic model which included bathymetric variations, was used to study detection ranges for an area in Arabian Sea. Azimuthal and seasonal SDR at octave bands within 500 Hz were determined at different receiver depths. Study shows that seasonal change in sound speed profile resulted in high SDR and noise level in winter at the location. Study also confirms the significant seasonal difference in detection range corresponds to the cut off frequency at 160 Hz. Detection range for a receiver at a depth 40 m is observed to be high across the azimuth and seasons of study.
3-D underwater parabolic equation model based on implicit finite difference method has been implemented for South Eastern Arabian Sea (SEAS). The bathymetric and geo-acoustic features have been integrated in the model for a 50 km circular region in SEAS. The model can simulate the effects of azimuthal variation in oceanographic features and compute azimuthally coupled pressure due to an omni-directional source. The azimuthal variation in oceanographic conditions can be observed during an upwelling event. In the first case study, the effect of upwelling event on three-dimensional acoustic propagation has been studied by using sound speed profile data derived from INS Sagardhwani observations. The difference in Transmission loss mosaic for upslope and downslope propagation is due to bathymetry as well as upwelling. In the second case study, the effect of upwelling only, is studied by running a model corresponding to range independent sound speed profile field and range dependent bathymetry. It was observed that during this upwelling event, the transmission loss is higher at longer ranges during upslope propagation than downslope propagation. This is due to the increase in the thickness of sonic layer duct as acoustic wave propagates from shallow to deep water. The effect of azimuthal variation i
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