Predictive methods for rain attenuation using radar and in-situ measurements tested against the 28-GHz Comstar beacon signal

A program to measure the rain attenuation of the Comstar beacon signal at 28.56 GHz has been in continuous operation since March of 1977 at Wallops Island, VA. During the summer of 1977 simultaneous radar and disdrometer measurements at the site were also made and used for predicting path attenuation. The best-fit values of and of the relation were deduced for each rain period from the raindrop size measurements, where is the attenuation coefficient [dB/km] and is the reflectivity factor [mm⁶/m³]. The measured relations and the simultaneous radar reflectivity measurements along the beacon path were injected into a computer program for estimating the path attenuation. Predicted attenuations, when compared with the directly measured ones, show generally good correlation on a case-by-case basis and very good agreement statistically after an empirical calibration adjustment is applied to the radar data. A method was also tested for predicting fade statistics at another frequency (e.g., 19 GHz) using simultaneous rain rate and fade distributions (28 GHz) in conjunction with disdrometer data. The predicted distributions showed good agreement with radar-predicted levels. The results demonstrate the utility of using radar in conjunction with disdrometer and rain gauge measurements for predicting fade events, long-term fade distributions, and establishing predictive criteria associated with earth-satellite telecommunications.