Non-Rayleigh reverberation characteristics near 400 Hz observed on the New Jersey shelf

A descriptive analysis of reverberation statistics is presented for data taken during the 2001 Acoustic Clutter Reconnaissance Experiment, which was conducted on the Office of Naval Research (ONR) STRATAFORM area off the coast of New Jersey. Large area plots of reverberation versus topography are presented as a lead-in to describe the statistics of the reverberation and clutter that were observed during this experiment. A comparison of polar plot appearance of spikiness with a measure of non-Rayleigh behavior seems to correlate reasonably well and suggests that the polar plots may be useful as such an indicator of non-Rayleighness. Statistical analysis of the reverberation showed that a moderate-to-large portion of the data examined were nearly Rayleigh and that most of the data (Rayleigh-like and non-Rayleigh) were well fit by the K distribution. The bistatic data were seen to be uniformly and significantly more non-Rayleigh than the monostatic data. This disparity is believed to be mostly accounted for by the lower reverberation-to-ambient noise power levels in the monostatic data and the smaller vertical beamwidth of the bistatic source, rather than having arisen from the bistatic geometry. Analysis of the shape parameter of the K distribution as a function of bandwidth illustrated the "bandwidth" effect where the shape parameter first decreases inversely proportional to bandwidth, but then increases in a trend back toward the Rayleigh distribution at higher bandwidths. The shape-parameter estimates are seen to be well fit by the elongated patch model of Abraham and Lyons. The monostatic data were observed to have a minimum occurring at a smaller bandwidth than for the bistatic data, a result explained by the larger time spread of the multipath expected for the monostatic source owing to its larger vertical beamwidth. Analysis of a small amount of data from the 2003 Acoustic Clutter Experiment, recently conducted on the New Jersey Shelf, predicts a smaller bandwidth for the minimum of the shape-parameter curve compared to the 2001 data. It is believed that the sound-speed profiles in 2003 lead to more bottom interaction than in 2001 and, therefore, produced a larger time spread in the multipath, leading to a minimum occurring at a lower bandwidth. The resu- lts of this paper indicate that many of the phenomena observed in the analysis of reverberation-envelope statistics may be explained by appropriately considering the effects of propagation in conjunction with the sonar system with which the environment is probed.