Segmented propagation model for the paths and travel times of surface duct leaky signals

In the deep ocean environment with a surface duct, sound propagating within the duct leaks into the geometric shadow zone below it. However, the propagation paths and time of these leaky parts have not been fully characterized. This paper investigates the mechanism of surface duct leaky (SDL) signals based on normal mode theory. It reveals that SDL signals are caused by specific modes with grazing angles close to zero at the bottom of the surface duct. Combining the theory of diffracted sound rays, the study proposes a Segmented Propagation model (SPM) for SDL signals. The propagation paths of SDL signals are divided into three segments: S1, which extends from the source to the surface duct; S2, the segment propagating within the surface duct; and S3, the segment leading from the surface duct to the receiver. The proposed SPM describes the propagation mechanism of SDL signals and allows for precise calculation of their propagation time. Experimental data from the western Pacific are used to verify the SPM.