Sound intensity variations in the presence of shallow-water internal waves passing through acoustic track

Fluctuations of low frequency pulses (LFM signals in 270-330 Hz band) in the presence of internal solitary wave (ISW) packet during the SW06 experiment are analyzed to quantify the interaction of sound with ISW field. Three situations during approximately 2 hours (20:30 - 22:30 GMT of August 17, 2006) are considered: a period when ISW was absent, a period when ISW started to intersect the acoustic track, and a period when ISW occupied the acoustic track. The propagation direction, velocity, and amplitude of the ISW were estimated from the on-board radar images recorded by two research vessels along with temperature records of sensors moored at the source, at the receiver, and between the source-receiver track. Modeal and frequency filtering of received pulses was carried out as well as analysis of temporal variations of the field depth distribution. This analysis allows us to identify two different acoustic fluctuation mechanisms: horizontal refraction and adiabatic variability, and it confirms the previously proposed theory on the sound field fluctuations due to ISW. Work was supported by ONR and RFBR.