Theoretical study of the evaporation duct effects on satellite-to-ship radio links near the horizon

A new approach to the calculation of radio wave propagation between a moving satellite and a ship, when the elevation angle is extremely low, i.e. as the satellite is rising or setting at the horizon, is described. In the paper the evaporation duct is considered as a dominant mechanism. Using reciprocity, the link is split into two parts: between the ship and a connecting interface, the parabolic equation method is used to model clear-air propagation; and propagation in free space is assumed between the satellite and the same interface. Then, using a coupling factor, the two parts of the link are connected on this interface, whose location depends an the elevation angle; an original approach to the determination of this interface is described. Then the model is applied to the study of the influence of the frequency value, and also to the influence of the roughness of the sea surface and of the existence of horizontal gradients in the refractive index distribution. Finally, some general ideas towards a radio wave characterisation method of the evaporation duct are presented