Shallow water acoustic amplitude fluctuations at 35 and 65 kHz

An underwater acoustics experiment conducted in shallow water (70 feet ) off the New Zealand east coast in 1972-1973 is described. Short acoustic pulses of 35 and 65 KHz sound were projected along near-orthogonal paths of approximately 300 yards. Environmental parameters were simultaneously observed. Statistical and spectral analyses of pulse heights were performed on 12 selected runs using digital techniques. Coefficients of variation ranged from 2.0% to 15.5%. In almost all cases, higher variability was observed along the acoustic path oriented perpendicular to the predominant swell direction. Along this same path, periods corresponding to common surface swell periods were frequently evident in the autocorrelation functions of the fluctuations. Coherence between the fluctuations along each path was low, averaging about 0.1. Long period oscillations suggestive of modulation by internal waves were apparent in several runs. No signif­icant dependence of variability on acoustic frequency was detected. Microscale temperature fluctuations measured simultane­ously are discussed.Naval Ordnance Systems Commandhttp://archive.org/details/shallowwateracou00korbLieutenant, United States NavyApproved for public release; distribution is unlimited