Wind fetch effect on underwater wind-driven sound

Abstract

This article presents the investigation of the wind-driven component of underwater ambient sound in the shallow brackish waters of the Baltic Sea. Natural sound levels are strongly correlated with the wind speed at high frequencies (≥5 kHz). At frequencies above 5 kHz, a characteristic spectral level decrease of 5 dB/octave was observed. Analysis of the data revealed that, for the same wind speed, the spectral levels are higher when the wind is blowing from a direction where the closest obstructing shore is farther away, i.e. the wind fetch is longer, which results in higher waves. This was especially noticeable in ambient sound recorded in a channel-like basin, where for the 8.5 m/s steady wind speed, the 5 kHz mean spectral level is 4 dB higher at the longer 152 km wind fetch versus the shorter 2.1 km wind fetch.

Keywords

• wind-driven sound
• shallow waters
• spectral levels
• wind fetch