Cancellation of Surface Reverberation from a Bistatic Sonar.

This report considers the cancellation of surface reverberation from the convergence zone CZ using an LMS multiple canceller structure. In CZ operations, this surface reverberation is often the limiting factor in the detection of low doppler targets. The multiple reference canceller approach is bistatic in that hydrophones spatially separated from the active sonar transmitreceive array are used as references to cancel the CZ surface reverberation. When the target is submerged below the CZ, providing spatial separation of the target and surface, it may be possible to spatially reject the CZ surface reverberation but not the target, allowing detection. The first phase of the study, reported in this document, concentrates on the ability of the canceller to reject the reverberation in the absence of signal. The CZ surface reverberation is modeled as an extended source with range extent limited by the width of the CZ and horizontal extent limited by the horizontal directivity of the transmitter. When viewed from typical convergence zone ranges, this source appears to have narrow angular extent. Using the narrow extended source model, expressions are developed for the second order statistics of the canceller output. Author