Some statistical properties of theambient noise in the Baltic Sea andits relation to passive sonar

Sammanfattning: The Baltic Sea Information on the Acoustic Soundscape (BIAS) is an European Union financed research project coordinated by FOI. The goal is to determine the soundscape of the Baltic Sea. This study is a part of BIAS and was focused on generating Wenz curves for the Bothnian Sea, which is a part of the Baltic Sea. Wenz curves describe the spectral noise level at different sea states. The investigation of the soundscape was done for both summer and winter conditions when the hydrographical situations differ. Further investigations of the noise dependencies of the natural and anthropogenic sound sources were performed. Wind and ships were dominating in a broad frequency band.The influence of ship noise on the ambient noise is dependent of frequency and distance. Ships within 5 km distance dominates the recorded noise levels and are not part of the ambient noise. At distances longer than 5 km a single ship becomes non-distinguishable and part of the range independent noise floor.Passive sonar ranges were calculated for two different sources. The range was shown to be clearly dependent on the sea state. With an increase of wind speed from sea state 0.5 to 3 the range increased with about 100%.The results of this study will be used in BIAS and in related research projects. It may be used for marine biologics but also for development of sonar and underwater systems.