Microwave Attenuation Statistics due to Rain along Earth-Space Path

37-39The rain attenuation statistics at 11 and 18 GHz derived from measurements by using microwave radiometers at 11 and 18 GHz over New Delhi are described. The measurements suggest that there are 50 and 325 occurrences when 10 dB fade level at II and 18 GHz. respectively, is equalled or exceeded. The cumulative distribution statistics for the period Sep. 1977 to Aug. 1978 suggest that for 0.017% of time, the annual attenuations are 7.4 and 13.0dB at II and 18GHz. respectively. The worst month is determined from the cumulative distribution to be Aug. 1978. It is found that the mean ratio of occurrences at the worst month to yearly statistics at 18 GHz for New Delhi is 6.2. The study of seasonal variation of rainfall and attenuation indicates that the probability of occurrence of a 10dB fade at 18 GHz during the period (Sep.-Nov. 1977) is approximately 15 times more compared to the winter period (Dec. 1977-Mar. 1978). Comparison has also been made between the measured attenuation statistics at National Physical Laboratory. New Delhi (India), and attenuation statistics obtained using radiometric techniques and direct satellite measurements at different places around the world