Observation of dispersion and azimuthal dependence of broadband acoustic signals in shallow water

A multi-institutional acoustic experiment was conducted in 1995 on the New Jersey continental shelf to examine the Shallow Water Acoustics in Random Media (SWARM'95). Two major source/receiver geometries were established. One was parallel to the continental shelf edge and the other was perpendicular to it. The parallel propagation consisted of two di square erent broadband sources transmitting signals nearly perpendicular to the internal wave propagation direction. These signals were a transient airgun source (0.1 sec duration) and a linear frequency modulated sweep (30 sec duration). Placed above and below the thermocline, these sources were transmitting signals every minute for few hours at a given range. The transmissions were received by two vertical line arrays at di square erent ranges and angles from the source. During the same period, the internal wave activity in the same region was measured and solitary wave interactions with acoustic signals along the two propagation paths are examined. A 10 to 15 minute temporal variations in the intensity of the received signals were observed. These temporal variations are azimuthally dependent on the variability of water column in the presence of internal solitary waves.