Preliminary analysis of wind-driven ocean ambient noise in the north area of Zhongsha during typhoon

Abstract

The characteristic of wind-driven ocean ambient noise had been analyzed in the north area of Zhongsha island. The hydrophone receiving depths is from 155m to 875m. It is shown that the correlation coefficient between the ocean ambient noise and the wind speeds is > 0.5 when the frequency is ≥ 500 Hz in non-typhoon periods. The correlation coefficient is decreased with the increase of hydrophone receiving depth when the frequency is ≥ 250 Hz. It is shown that the ocean ambient noise in this frequency band had been mainly generated from the wind-driven noise sources near the sea surface. In typhoon period, the correlation coefficient between the ocean ambient noise and the wind speeds is > 0.55 when the frequency is ≥ 250 Hz and it is nomadically increased with the increase of receiving depth. It is shown that the wind-driven ocean ambient noise had also been originated from long distances and not only local sources. It may be deduced that the ocean ambient noise traveling along the slope of seafloor was received by the hydrophones. The ocean ambient noise was coming from the stormy waves beating against the islands of Zhongsha and Xisha in typhoons. This is called the “down-slope conversion effect”. The lower frequency limit of wind-driven ocean ambient noise has even been decreased by the typhoon effect. The variable ambient noise levels at different receiving depths will be attributed to acoustic propagation effect of the special sea-floor terrain in the measurement sea zone.