Rain attenuation on a satellite link on the western coast of Norway

Abstract

Simultaneous 19.68 GHz beacon and precipitation measurements from Bergen at the west coast of Norway are described and analyzed. The measurement site is located at 60° North and 5° East, resulting in a 21.5° elevation angle towards the geostationary Eutelsat Ka-Sat satellite at 9° East. This location experiences high amounts of precipitation during the year, with total amount comparable with tropical locations. An earlier detailed meteorological study of the long-term measurements of rain rate in the area has shown large differences between measured values and the values given by the ITU-R global numerical maps. The two years of measurements analyzed in this paper show rain rate similar to the ITU-R values while attenuation is significantly above ITU-R predictions for high exceedance percentages and below for low percentages. High rain intensity values were recorded some of the winter months while the rain attenuation in the same periods was low. This apparent discrepancy is caused by significantly lower rain height which leads to a shorter path length below rain. The frequent low attenuation events indicate that the distribution of rain attenuation used by the ITU-R model might not adequately reflect the specifics of rain events in coastal regions. More importantly, the measured data and rain probabilities highlight a gap in the current ITU-R models for percentages of time above 5 percent. For this location, attenuation was measured for up to 30 percent of time, where the magnitude is not predicted by the ITU-R models, even though the predicted probability of rain attenuation along the path matches the measurement.