A Study on the Propagation Characteristics of AIS Signals in the Evaporation Duct Environment

The propagation characteristics of the Automatic Identification System (AIS) in the evaporation duct environment over the sea surface are investigated by using the parabolic equation method. The parabolic equation method has excellent stability and accuracy in solving the computational problem of electromagnetic wave propagation under different atmospheric conditions and it is probably the most suitable for the purpose of analyzing AIS signals. The propagation of AIS signals in air is determined by the variation of the refractivity with height. For AIS transmission, ducting propagation may be the most important propagation mechanism. The propagation loss of AIS signals in the evaporation duct is simulated and compared with that for the case of the standard atmosphere. The simulation results show that evaporation duct has little influence on the AIS signals.