Reverberation vertical coherence and sea-bottom geoacoustic inversion in shallow water

Optimal array-processing techniques in the ocean often require knowledge of the spatial coherence of the reverberation. A mathematical model is derived for the reverberation vertical coherence (RVC) in shallow water (SW). A method for analysis of RVC data is introduced. Measured reverberation cross-correlation coefficients as a function of time and frequency, obtained during the Asian Seas International Acoustic Experiment (ASIAEX) in the East China Sea, are reported. SW reverberation from a single shot provides a continuous spatial sampling of the surrounding sound field up to several tens of kilometers and holds valuable information on the geoacoustic properties of the sea floor over this distance. SW reverberation data can, therefore, be used as the basis for a quick and inexpensive method for geoacoustic inversion and has the obvious advantage that acquiring the data in situ requires only a single platform. This paper considers the use of the vertical coherence of the reverberation as the starting point for such an inversion. Sound speed and attenuation in the sea bottom at the ASIAEX site are obtained over a frequency range of 100-1500 Hz by finding values that provide the best match between the measured and predicted RVC.