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Research on Underwater Acoustic Target Depth Classification Based on Modal Filtering Characteristics of Long Horizontal Line Array

Considering the problem of depth classification of underwater acoustic targets in shallow water, a classification method based on modal filtering characteristics of long horizontal line array(HLA) beamforming in a negative thermocline environment was proposed. Based on normal mode theory, the spatial filtering characteristics of long HLA are studied by beamforming, and it was found that this characteristic can filter a normal mode. In the negative thermocline environment, the acoustic fields excited by deep and shallow sources and received by deep receivers are controlled by different modes. Surface reflection bottom reflection (SRBR) mode and non-surface reflection bottom reflection (NSRBR) mode show different interference structures in range-spectrum. Based on the characteristics of modal filtering and sound field classification, a depth classification method for shallow water acoustic targets in a negative thermocline environment is established. Numerical results show that the proposed method is robust and can effectively distinguish the acoustic source targets above or below the thermocline (surface and underwater targets) without knowing the specific acoustic environment parameters in advance.