Matched Field Detection in the Shadow Zone of Deep Water With a Hybrid Replica Combining Various Eigenray-Interactions

Passive source detection in the shadow zone of deep water represents a critical challenge in underwater acoustic measurement systems, which requires balancing multipath energy utilization against independence from environmental parameters. The matched field detector (MFD) incorporates multipath propagation effects into its replica field modeling, thereby inherently utilizing multipath energy. However, this method requires a priori knowledge of environmental parameters for replica computation, imposing significant practical constraints. To reduce this dependency, previous approaches have simplified the replica construction by using two equal-amplitude interference components, each from the interaction of two eigenrays along distinct bottom-reflected paths (termed eigenray pairs). However, the distinct interactions can introduce amplitude inconsistencies between the components, leading to replica mismatches. This study addresses this limitation by introducing a novel hybrid-replica design that systematically incorporates component-amplitude variations across source positions. The detection area is categorized into three regions based on dominant interference components, each associated with its specialized replica type. We then propose a hybrid replica that combines these replica types and derive the matched hybrid-field detector. Simulation and experimental validations using underwater acoustic measurement systems demonstrate that the hybrid replica effectively mitigates amplitude mismatches, enabling matched hybrid-replica field detector (MHFD) to achieve detection performance comparable to conventional MFD with significantly reduced reliance on environmental parameters.