Tropospheric radio-wave propagation over mixed land and sea paths

Field-strength measurements of a transmission at 560 Mc/s over the North Sea from the Dutch coast were carried out at five sites which were approximately collinear with the transmitter, the first being situated on the English coast and the others progressively further inland. The lengths of the paths ranged from 198km to 356km. The results show that the attenuation relative to an all-sea path, introduced by land at the end of the path, increases with the distance from the coast. A method of estimating the attenuation due to the presence of land in the path is described. Field strengths calculated by this method for the experimental paths are compared with the measured results. Comparisons are also made with the existing CCIR method of estimating field strength over mixed land and sea paths.