Phase Spreading in Directly Transmitted Sound-Wave Packets

A short sound pulse, transmitted horizontally between two points in deep ocean water, arrives at the receiver as a continuous superposition of time-separated wave packets. This fact has been demonstrated by a detailed analysis of the cross covariance between such pulses carrying a phase reversal and a truncated replica. In all, about 280 pulses were selected from over 3000 which were previously studied (N. W. Lord, J. Acoust. Soc. Am., 36, 1043 (A), 1964) for the transmission-time fluctuation. For these 1200 cps pulses the phase spreading becomes tangible at a range of 7 km where it is approximately 0.2 msec. As an estimate of instantaneous phase spread, this value is reasonable compared to the transmission-time fluctuation, for this range, of 0.7 msec between pulses spaced every 0.6 sec. The use of a truncated replica on a long pulse depresses most of the side-lobe cross-covariance peaks. The magnitude of the central peak is related to both the phase spreading and the chosen length of the truncated replica, although this latter dependence is lost by a slow phase reversal. Presented at the Acoustical Society of America Meeting (71st) 1-4 Jun 66, Boston, MA.