USE OF AMBIENT SOUND MEASUREMENTS IN AN INTEGRATED SYSTEM FOR OCEAN MONITORING

Abstract

Measurements of underwater sound were made at 16 frequencies in the range 500 Hz ­ 50 kHz using 3 moored hydrophones located off the west coast of Ireland during Oct-Nov 2003. These data have been analysed in relation to environmental conditions, particularly wind speed and rainfall. Although there are some unexplained offsets in the overall acoustic levels compared with those obtained by other researchers, it has proved possible to develop a classification scheme enabling wind, drizzle, rain, and contamination to be separately identified. The acoustic data can be used to infer wind speed to within 2 m s-1. There is also useful skill in the detection of drizzle and rain events, and some encouraging results in the quantitative estimation of rain-rate have been achieved. Comparisons have been made with deployments of the hydrophones off SW England and Canada. It is found that when precipitation is absent, underwater sound can be predicted from wind speed alone to an accuracy of ±1dB provided the winds are not light. Suggestions are made as to how such a subsurface technique might be combined with spaceborne measurements to enable estimates of underwater sound levels globally. The feasibility of using hydrophones within the Argo float programme should be explored