This paper addresses the problem of using a vertical aperture to suppress the interference caused to SAS by surface bounce path reverberation components decorrelated by the rough sea surface. Using at-sea gathered SACLANTCEN vertical array acoustic data, we characterize the reverberation vertical properties and investigate the separation of the direct and surface bounce path reverberation and target echo components. We propose two implementations of the PCI method of interference cancellation and demonstrate with actual data that they are effective in separating the reverberation in the vertical domain. I. BACKGROUNDThe detection of objects buried in the seabed by sonar has scores of applications, including mine hunting, cable and pipeline surveying, and archaeological research. This is a challenging problem. The physics of sound penetration into the seabed is a complicated phenomena that is governed by the frequency and the angle of the impinging acoustic field relative to the bottom interface. For grazing angles above the critical angle, Snell's theory predicts that sound will refract into sediment albeit with attenuation [l]. Since sediment attenuation [2] increases as a function of frequency, present day high frequency mine hunting sonars operating at hundreds of lcHz are ineffectual for detecting buried mines. However, the situation is better at low frequencies, e.g., in the 2-16 lrHz frequency band. Recently, investigators at SACLANTCEN 113 and elsewhere have found that there is substantial low frequency sound penetration into the sediment at angles above the critical angle and also at subcritical angles. At above critical angles, a SACLANTCEN study [l] found that buried mines were easily detectable in the 2-16 kHz frequency band, even down to a 50 cm burial depth.

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