135-139<span style="font-size:9.0pt;line-height:
115%;font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:hi"="" lang="EN-US">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.</span