ANALYSIS OF FLUCTUATIONS IN WIND DEPENDENT SHALLOW WATER AMBIENT NOISE SPECTRUM

Abstract

In this work, the fluctuations in the spectrum level of shallow water ambient noise is analyzed for 3 different sea states. The shallow water ambient noise data were collected of Bay of Bengal using an omni directional hydrophone and a portable data acquisition system.100 sets of data were collected and organized according to the three different sea states using Beaufort scale. Fluctuations in noise spectrum level at different sea states were studied by dividing the spectral bandwidth of 12 kHz into low, mid and high frequency bands. Mean noise spectrum level for each sea state was calculated and the result shows the noise spectrum level increases with the sea state. Further it was found that the noise level was higher in lower frequency band and decreases in the higher frequency band. Also the correlation between the noise level and sea state was higher in the low frequency band and tend to decrease in the mid frequency band and there was no correlation in the higher frequency bands. The higher noise levels were associated with lower frequencies of the bandwidth whereas it is less in higher frequencies. The fluctuations were found to be higher in the lower frequency band than the mid and higher frequency band. In this paper the data collection, data processing and noise spectrum analysis are presented in detail. As the fluctuations in power spectrum level of the ambient noise is one of the primary factor which decides the signal to noise ratio of most of the acoustic instruments, these results seems to be significant.