Over-the-horizon propagation characteristics of AIS signal in the elevated duct

The atmospheric duct can trap the radio wave signal and make it spread beyond the horizon, which affects the application of radio system signal propagation prediction and performance evaluation. In this paper, the characteristics of the elevated duct are analyzed based on sounding data. The deterministic method of radio wave propagation in the troposphere is used to simulate the shore-ship automatic identification system (AIS) propagation link, and the over-the-horizon propagation characteristics of AIS signals under different elevated duct environments are quantitatively studied. The results show that the AIS signal propagates significantly beyond the line of sight in an elevated duct with a duct strength of 50 M units and a bottom height of about 7 m; the strongly elevated duct environment with a duct bottom height of more than 700 m can also affect the propagation of AIS signals; compared to a single elevated duct model, the composite elevated duct (composition of two elevated duct layer structures) environment has a greater impact on AIS signal propagation. The results can provide important theoretical reference for the application of atmospheric duct monitoring inversion, radio system design, equipment effect evaluation, etc.