FREQUENCY-DEPENDENCE OF BROAD-BAND PROPAGATION IN COASTAL REGIONS

To study the frequency-dependent spatial and temporal variabilities of sound propagation in coastal regions two experiments were conducted b y transmitting sound impulses in the form of M sequences centered from 0.6 to 22 kHz. The site of the first experiment was the Atlantic Gene rating Station (AGS) where the source-receiver range was 214 m. The si te of the second experiment was Delaware Bay where the range was appro ximately 760 m. The mean water depth was 14-15 m in both locations. Oc eanographic data and acoustic data were collected simultaneously in bo th experiments. It was found that the temporal coherence of the propag ated broadband signal changes significantly with pulse center frequenc y, as well as varying with geographic location and time. Trends of inc reasing signal decorrelation (between consecutive pulses) with increas ing center frequency, and increasing signal decorrelation for paths wi th increasing number of interface interactions, were observed. It was found that for lower center frequencies there is hardly any decorrelat ion in signal over several hours, while for signals with center freque ncies only a few kHz higher there was substantial decorrelation over t imes as short as 10 to 20 min. No significant spatial decorrelation of the signal was observed over the hydrophone spacing of a few meters f or these experiments. (C) 1997 Acoustical Society of America.