Reverberation offers one of the most important backgrounds for the active sonar. Most of the researches focused on the average intensity loss or the statistic of the reverberation. However, the interference between normal modes is one of the most important characteristics, widely applied to geo-acoustic inversion, array signal processing, and source localization. Very few researches have studied the interference structure of reverberation.

Waveguide invariance has been widely used to describe the interference structure of sound propagation. The waveguide invariance reveals that the sound intensity has striations in the range-frequency distribution, and the slope of the striations is described as waveguide invariant. It should be pointed out that the waveguide invariant is not a constant. It depends on the location of the source and receiver, frequency and sound speed profile. However, relatively few studies have discussed the structure of the reverberation in the time-frequency distribution.

So LI Fenghua, ZHANG Yanjun, ZHANG Renhe and LIU Jianjun of National Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences carried out a series of studies and explained the striations of the reverberation intensity in the time-frequency distribution, which were observed in a shallow water acoustic experiment. They develop a model explanation following the coherent reverberation model. To examine the consistency between the measured data and numerical predictions, they use a method based on Radon transform for determining the slope of the striations to the measured data and numerical predictions. The results indicate that the coherent reverberation model developed can predict the interference structure of the reverberation intensity in the time-frequency distribution. 

This research result was published on the recently issued journal of Science China (Physics, Mechanics and Astronomy) ( Vol. 53, No. 8, August 2010).