Modeling of wind induced ambient noise vertical directionality and its variation due to bottom characteristics in shallow Arabian Sea

摘要

In underwater acoustics, knowledge regarding vertical structure of ambient noise has got lot of interest since it improves the design and performance of sonar systems. In this work the influence of ocean environment on wind induced vertical directionality of ambient noise has been analyzed using a model based on ray theory. Shallow water site off the Cochin coast at 30 m depth in Arabian Sea was chosen for studying the characteristics of vertical directionality. Variation of vertical directionality with respect to frequency, Sound speed profile and sediment properties were analyzed and the result clearly shows the importance of those environmental factors on directionality. Vertical directionality of summer and winter sound speed profiles was almost similar except for the broadside, where the effect of noise notch is prominent. Based on the difference in bottom reflectivity significant variation in intensity was observed for different sediment compositions. Variation of directionality with frequency clearly indicates the limitation of ray theory at low frequency. Finally the simulated directionality at different frequencies were compared with field measurements and the model results fits relatively well with the field data.