Near-caustic behavior in a 270-km acoustical experiment

Data from a pulse-propagation experiment are analyzed to quantify fluctuations in the transmitted acoustic signal. In the experiment a bottom-moored, broadband source having a 460-Hz center frequency transmitted 273 km away to a bottom-moored, vertical hydrophone array spanning 180 m of the water column. Pulses were transmitted every 12 min for a total duration of nearly 100 h. Because the minimal hydrophone separation at the receiving array was less than 2 m, vertical behavior on small scales could be observed. Furthermore, the vertical position of the receiving array enabled an examination of the near-caustic portion of wavefronts, and in some cases, the caustics themselves. Unfortunately, because instrument motion measurements were unsuccessful, relative rather than absolute signal fluctuations were the principal observable in this analysis.