A Coupled Mode Reverberation Theory for Clutter Induced by Inhomogeneous Water Columns in Shallow Sea

The detecting performance of active sonar in shallow sea is restricted by seabed reverberation and clutter. In this paper, the seabed reverberation and target-like clutter caused by inhomogeneous water columns are modelled by coupled mode reverberation theory. Taking nonlinear internal waves (NIWs) as examples of the common inhomogeneous water columns, mode coupling matrices are derived by coupled mode to describe the process of energy exchange and mechanism of reverberation clutter. It is found that the oscillation phenomena of the reverberation intensity which is after the clutter arrival are well explained by the coupled mode theory and the oscillation periods are connected with the speeds of nonlinear internal waves. A theoretical basis is proposed in this research for identifying strong interferences of clutter caused by NIWs. Meanwhile, the oscillation mechanism is expected to realize the monitoring of internal waves.