A 50 h acoustic propagation experiment conducted during SW06 included receptions of broadband signals at three ranges with single hydrophone receiver units. 100-1600 Hz centered broadband signals were propagated through identical shallow channels during periods of low- and high-internal wave energies. Here, the transition from nearly perfect coherent and stable mode/ray arrivals to the formation of short live micromodes/ray arrivals is presented. The relative influence of volume scattering and bottom scattering is seen to shift with frequency; low frequencies see a smooth reflective bottom but have interaction with internal waves induced volume fluctuations, whereas higher frequencies are increasingly more sensitive to bottom scattering. Discrete mode arrivals give way to continuum of numerous short lived arrivals with increasing frequency. For still higer frequencies, coherence times are shorter still and at some point the phase coherence is so reduced that signal processing gain is lost and the signals are no longer detectable. Ultimately, the performance of higher-frequency sonar and underwater communication systems will be limited by these effects. The limits of phase coherenct gain for the 800 and 1600 Hz signals are estimated for this range site.

Back to the main WHOI SW06 home

	© Woods Hole Oceanographic Institution                         © University of Washington
	Last updated July 2007