Near-caustic behavior in a 270-km acoustical experiment

Data from a pulse-propagation experiment are analyzed to quantify fluctuati ons in the transmitted acoustic signal. In the experiment a bottom-moored, broadband source having a 460-Hz center frequency transmitted 273 km away t o a bottom-moored, vertical hydrophone array spanning 180 m of the water co lumn. pulses were transmitted every 12 min for a total duration of nearly 1 00 h. Because the minimal hydrophone separation at the receiving array was less than 2 m, vertical behavior on small scales could be observed. Further more, the vertical position of the receiving array enabled an examination o f the near-caustic portion of wavefronts, and in some cases, the caustics t hemselves. Unfortunately, because instrument motion measurements were unsuc cessful, relative rather than absolute signal fluctuations were the princip al observable in this analysis. (C) 1999 Acoustical Society of America. [S0 001-4966(99)01706-3].