Source depth classification in shallow sea negative thermocline waveguide with small aperture vertical arrays

Abstract

In a shallow sea waveguide with a negative thermocline, the sound field elevation structure depends on the source depth and can be utilized for source depth classification. This paper focuses on vertical arrays deployed below the thermocline, with an aperture smaller than half the water depth, and constructs a sound field elevation structure model based on normal mode theory. The study reveals the differences in the sound field elevation structure characteristics between surface and submerged sources: stronger-intensity sound field elevation structures for surface sources appear in the free mode angular region, while those for submerged sources appear in the trapped mode angular region. Based on the dependence of the sound field elevation structure on source depth, a new source depth classification method is proposed. The method utilizes the Trapped Mode-Free Mode sound field elevation structure strength ratio as a decision metric and provides the corresponding classification criteria. Simulation verification and sea trial data processing confirm the feasibility and effectiveness of the proposed method, showing good classification capabilities even with small aperture vertical array conditions and robustness to environmental mismatches.