Archipelago Ambient Noise and its dependence on weather.

Experiences from many field experiments indicates that the ambient noise (AN) in the Baltic does not always follow the standard Wenz curves, expressed as a function of wind speed. Many times, the measured AN has been found to be lower than the standard values, especially in the archipelago. Knowledge about AN is important in many situations, especially for navies doing anti-submarine warfare (ASW) with passive sonar. When an ASW operation is planned, it is important to have the right levels of AN to get correct values for detection distances in order to optimize the ASW tactic. The Swedish Defence Research Agency (FOI) has therefore carried out an experiment with the objectives to better understand how AN depends on the weather. The experiment lasted for 16 days, with winds varying between 0 and 36 knots, corresponding to sea-states 0 - 8. As there was sea traffic and acoustic communication in the experimental area, a special anthropogenic filter was constructed, which filtered out the noise coming from these sources. The results indicate that the AN in the archipelago is dependent on both fetch and wind speed. When the fetch is short, the AN is much lower than predicted by standard curves. [ABSTRACT FROM AUTHOR]