A review of passive detection and recognition of underwater acoustic weak targets: progress and perspectives

Underwater acoustic weak target detection and recognition is one of the most challenging tasks for passive sonar systems. Generally, the difficulty comes from three aspects. First, the complicated ocean environment (e.g., the medium inhomogeneity, the multiple interface scattering, the dynamically changing acoustic channel) makes the sound propagation difficult to calculate and predict. Second, the increasingly noisy environment results in a relatively high noise level. Third, the continuously improving stealth capability of the target leads to an extremely low source level, which significantly reduces the detection and recognition ranges of passive sonars. Alternatively, the physics-based high-gain processing methods and artificial intelligence-based methods offer potential solutions. This paper provides a review of methods particularly developed for the passive detection or recognition of underwater acoustic weak targets. It also summarizes some major challenges and gives several suggestions for future research.