Automatic Identification System Signals propagation in troposphere ducting conditions

This work draws the attention on the influence of tropospheric ducting on the propagation of Automatic Identification System (AIS) frequencies. The propagation of AIS signals in the cases of elevated range-dependent and surface-based range-dependent ducts formed by elevated trapping layers is studied. The importance of the accuracy of the refractivity profiles' approximation is briefly discussed. The AIS signals propagation is modeled by the parabolic wave equation method for which the refractivity profiles serve as environmental input. The propagation simulations results show that the AIS frequencies can be more affected by elevated trapping layers leading to the formation of elevated ducts than by large surface-based ducts also formed by elevated layers. The results once again outline that the reconstruction of refractivity profiles must be as accurate as possible and that for long maritime paths multiple profiles may be needed to obtain reliable AIS data.