Further analysis of intensity fluctuations from a 3252-km acoustic propagation experiment in the eastern North Pacific Ocean

In the Acoustic Thermometry of Ocean Climate (ATOC) program's Acoustic Engi neering Test (AET), broadband 75-Hz center frequency transmissions were rec orded on a 700-m-long vertical array, 3252 km distant from a midwater sourc e suspended from R/P FLIP. The transmissions occurred over a 6-day period. Previously reported results from the AET using 12.7-min averaged data by Co losi et al. [J. Acoust. Sec. Am. 105(6), 3202-3218 (1999)], hereafter refer red to as Colosi99) revealed surprisingly weak acoustic scattering for earl y arriving identifiable wavefronts. Colosi99 found pulse time spreads on th e order of 0-5 ms and the probability density function (PDF) of peak intens ity was close to log normal. In this paper these results are confirmed usin g 1.8-min averaged data. It is also shown that scintillation index (SI) is a strong function of position along the pulse with the smallest values occu rring at the peak and larger values occurring at the tails. Intensity PDFs of identifiable wavefronts are reanalyzed in terms of both peak intensity a nd integrated pulse energy (IE) where the integration is over +/- 50 ms fro m the wavefront peaks. While SI for the IE are somewhat smaller than for th e peak intensity, the PDFs are both very closely log normal. Regarding mult ipathing along the wavefronts, it is found that on average there are 1.7 pe aks per wavefront segment per hydrophone and the intensity PDF of all multi path peaks is log normal. The combined observation of weak scattering and m ultipathing is a novel result. A reanalysis of the scintillations in the AE T transmission finale where no wavefronts are evident is presented. Colosi9 9 analyzed the finale in terms of peak scintillations and found a near log- normal intensity PDF. Reprocessing the full field without limiting data to intensity peaks and accounting for mean intensity nonstationarity yields an intensity PDF which is much closer to the exponential distribution associa ted with full saturation; these results show that the finale region can be expected to behave much like Gaussian random noise. (C) 2001 Acoustical Soc iety of America.