Rain Attenuation on Earth-Satellite Paths - Summary of 10-Year Experiments and Studies

In 1967 and 1968, the Bell System used a suntracker during the day and a radiometer during the night to measure rain attenuation statistics on earth-space paths because there were no strong signal sources in space available for measurement of large rain attenuation on earthspace paths, except the sun. 1 These pioneer experiments 1 " 1 have contributed significantly to the understanding of rain attenuation phenomena on earth-space paths. An excellent review of these early experiments can be found in Ref. 5. However, the antenna elevation angle of the suntracker is not constant. For direct application to satellite communication systems, it is desirable to measure rain attenuation statistics with fixed antenna elevation angle. The radiometer technique can fulfill this need by measuring rain-originated thermal noise with a constant antenna elevation angle.6,7 In other words, the radiometer technique does not require any active signal source in space such as the sun or satellite beacons. The dynamic range of the radiometer technique for rain attenuation measurement is approximately 10 dB. By simultaneous measurements at Holmdel, New Jersey, using a 16-GHz radiometer and a 15.3 GHz receiver for the NASA ATS-5 beacon signal, A. A. Penzias 8 first verified the accuracy of the radiometer technique in 1969. Since 1969, the Bell System has been conducting continuous rain attenuation experiments at microwave frequencies on earth-satellite paths with constant antenna elevation angle in New Jersey, Georgia, Illinois, and Colorado.