A study on Ka band rain attenuation for LEO satellite over Taiwan area

It is recognized that rain attenuation is a primary factor in the degradation of the Earth-satellite communication at the frequency of Ka band. In this paper, on the basis of 8 years (1988-1995) rainfall rate data at one-minute time resolution recorded by more than 70 tipping bucket rain gauges distributed over Taiwan island, the spatial distribution of the long-term statistics of rainflall rate is investigated. The results show that there is a pronounced latitudinal variation in the percentage of the time that the rainfall rate exceeds a specified level, indicating that more severe rain attenuation will be encountered in the southern part than that in the northern part of Taiwan. In addition, the sky noise temperature at the frequency of 19.5 GHz is also measured by using a radiometer both in the conditions of clear-air and precipitation. In the case of clear-air sky, the observed sky noise temperature, increasing exponentially with the decrease of the zenith angle in an excellent agreement with the theoretical prediction, at the elevation angles of 90°, 60°, 30°, and 15° are respectively 40K, 46K, 72K, and 128K. For the case of precipitation, the comparison between observed sky noise temperature and surface rainfall rate is made, showing a good correlation between them.