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 descri bed. In the paper the evaporation duct is considered as a dominant mec hanism. Using reciprocity, the link is split into two parts: between t he ship and a connecting interface, the parabolic equation method is u sed to model clear-air propagation; and propagation in free space is a ssumed between the satellite and the same interface. Then, using a cou pling factor, the two parts of the link are connected on this interfac e, whose location depends on the elevation angle; an original approach to the determination of this interface is described in the paper. The n 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 a nd of the existence of horizontal gradients in the refractive index di stribution. Finally, some general ideas towards a radio wave character isation method of the evaporation duct are presented.