Depth-based suppression of moving interference with vertical line arrays in the deep ocean

Abstract

Vertical line arrays (VLAs) deployed below the critical depth in deep ocean environments can exploit the reliable acoustic path (RAP), which exhibits low transmission loss (TL) at moderate ranges and increased TL for distant interference. However, nearby surface ship interference presents a major challenge for an array lacking horizontal aperture that doesn’t provide bearing discrimination. The motion of the interference degrades covariance estimation and limits observation intervals, thus limiting adaptive rejection capabilities. An image-method interpretation of the propagation physics reveals a depth-dependent modulation feature which enables separation of signals originating from near-surface and those from sub-surface passive acoustic sources. This discrimination can be achieved in the data through an integral transform. The feature is robust to environmental variability and allows for rejection of near-surface interference and depth classification. The transform-based filter is derived in closed form, and demonstrated with simulation results for a deep ocean environment with multiple moving surface interferers.