| Popis: |
Three long-range 2 GHz radio paths have been established in the British Channel Islands in order to investigate the characteristics of long-range propagation of UHF radio waves over the sea as part of a project supported by Ofcom, UK. The relationship between specific over-sea propagation mechanisms (such as evaporation ducting and super-refraction) in the lower troposphere and signal strength distribution patterns has been examined, modelled and correlated with meteorological parameters. A number of radio meteorological statistics specifically related to evaporation duct propagation in a temperate region such as the English Channel has been presented to confirm the capability of this key propagation mechanism to guide radio waves to distances well beyond the normal radio horizon. Evaporation ducting and diffraction appear to be the dominant propagation mechanisms at most times. Signal strength enhancements have been observed on all three radio paths, primarily in the late afternoon and evening periods, in the spring and summer months. During periods of enhanced propagation, which occur approximately 8% of the time of a 50 km path, the presence of additional higher-level ducting/super-refractive structures has been verified and their influence has been modelled with reasonable success. Additionally, the statistical variation of bulk meteorological parameters in the context of enhanced signal propagation has also been examined. The relatively long-term observations made during this study confirm the fact that the constantly changing weather patterns in the troposphere (e.g. the occurrence of anticyclonic weather) are directly responsible for the occurrence of enhanced signals at certain periods of time. The various issues under investigation are of direct relevance in the planning of radio communication systems operating in the UHF band (e.g. GSM and UMTS) in marine and coastal regions. |
